ANSI-AGMA 2004-B89-Gear Materials and Heat Treatment Manual

ANSI/AGMA 2004---B89(Revision of AGMA 240.01) January 1989 Reaffirmed October 1995 AMERICAN NATIONAL STANDARD Gear Materials and Heat Treatment Manual Gear Materials and Heat Treatment Manual Gear Materials And Heat Treatment Manual AGMA 2004---B89 (Revision of AGMA 240.01) [Tables or other self---supporting sections may be quoted or extracted in their entirety. Credit lines should read: Extracted from AGMA 2004---B89, Gear Materials and Heat Treatment Manual, with the permission of the publisher, the American Gear Manufacturers Association, 1500 King Street, Suite 201, Alexandria, Virginia 22314.] AGMA Standards are subject to constant improvement, revision or withdrawal as dictated by experience. Any person who refers to an AGMA Technical Publication should be sure that the publication is the latest available from the Association on the subject matter. ABSTRACT The Gear Materials and Heat Treatment Manual provides information pertaining to engineering materials and material treatments used in gear manufacture. Topics included are definitions, selection guidelines, heat treatment, quality control, life considerations and a bibliography. The material selection includes ferrous, nonferrous and nonmetallic materials. Wrought, cast, and fabricated gear blanks are considered. The heat treatment section includes data on through hardened, flame hardened, induction hardened, carburized, carbonitrided, and nitrided gears. Quenching, distortion, and shot peening are discussed. Quality control is discussed as related to gear blanks, process control, and metallurgical testing on the final products. Copyright E, 1989 Reaffirmed October 1995 American Gear Manufacturers Association 1500 King Street, Suite 201 Alexandria, Virginia 22314 February 1989 ISBN: 1---55589---524---7 ANSI/AGMA ii 2004---B89 Gear Materials and Heat Treatment Manual FOREWORD [The foreword, footnotes, and appendices, if any, are provided for informational purposes only and should not be construed as part of AGMA Standard 2004---B89 (Formerly 240.01), Gear Materials and Heat Treatment Manual.] The Standard provides a broad range of information on gear materials and their heat treatment. It is intended to assist the designer, process engineer, manufacturer and heat treater in the selection and processing of materials for gearing. Data contained herein represents a consensus from metallurgical representatives of member companies of AGMA. This Standard replaces AGMA 240.01, October 1972. The first draft of AGMA 240.01, Gear Materials Manual, was prepared in October 1966. It was approved by the AGMA membership in March 1972. Reprinting of AGMA 240.01 for distribution was discontinued in 1982 because it had been decided in 1979 by the Metallurgy and Materials Committee to revise its format. The initial draft of AGMA 2004---B89 (formerly 240.01) was completed in April, 1983. Work continued on the Standard with numerous additional revised drafts within the Metallurgy and Materials Committee until it was balloted in 1988. It was completed and approved by the AGMA Technical Division Executive Committee in September 1988 and on January 23, 1989 it was approved as an American National Standard. Suggestions for the improvement of this standard will be welcome. They should be sent to the American Gear Manufacturers Association, 1500 King Street, Suite 201, Alexandria, Virginia 22314. ANSI/AGMA iii 2004---B89 Early. E. L. Winterrowd (Cummins Engine) T. Mumford (Alten Foundry) G. Inc. L. Heller (Peerless Winsmith) D. Shoulders (Reliance Electric) (Deceased) M. E. L. Tipton (Caterpillar) D. Swiglo (IPSEN) S.Gear Materials and Heat Treatment Manual PERSONNEL of the AGMA Committee for Metallurgy And Materials Chairman: L. J. Jr. J. D. Milburn (The Gear Works --. Hillman (Westinghouse. Rivart (CLECIM) R. C. R. Sanderow (Supermet) R.) Vice Chairman: G. Black (General Motors) E. R. Craig (Cummins Engine) T. Andreini (Earle M. Guttshall (IMO Delaval) W. L. M. D.) L. K. P. Tanaka (Nippon Gear) R. R. L.Muncie) J. Lemanski (Sikorsky) ANSI/AGMA iv 2004---B89 . Sueyoshi (Tsubakimoto Chain) M. Houck (Mack Trucks) A. Vaglia (Farrel Connecticut) T. Milano (Regal Beloit Corporation) A. Cary (Metal Finishing) H. McVittie (The Gear Works --. Wiskow (Falk) ACTIVE MEMBERS N. K. Inc. Abney (Fairfield Manufacturing) R. Air Brake) B. Partridge (Lufkin) E. L. J. Smith (Invincible Gear) Y. Arnold (Xtek. F. E. A. Berndt (C and M of Indiana) J. J. I. Jorgensen) E. P. L. W. Schwettman (Xtek. Hoffmann (Dresser) L.) R. Cunningham (Boeing) P. H. Carrigan (Emerson Electric) P. Shapiro (Arrow Gear) W. Olson (Cleveland) J. Horvath (G. Burrell (Metal Improvement Co. J. H. Rickt (Auburn Gear) H.Seattle) ASSOCIATE MEMBERS R. Vukovich (Eaton) L. B. Bruce Kelly (General Motors) D. A.Seattle) P. E. S. (Gleason) A. Chevrolet --. Bergquist (Western Gear) J. Glew (Prager) D. M. Starozhitsky (Outboard Marine) A. Witte (General Motors) M. Gayley (IMO Delaval) J. Inc. G. Giammarise (General Electric) J. Leslie (SPECO Corporation) B. Bonnet (WesTech) N. . . . . . . . . . . . . . . . . . . . . . Ferrous Gearing . . . . . . . . . . . . . . . . Quenching . . . . . . . .5 6. . . . . . . . . . . . . . . . . . . . . . . . . Distortion . . . . . . . . . . . . . . . . . 25 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 6.Gear Materials and Heat Treatment Manual Table of Contents Section Title Page 1. . . . . . . . . . . . . . .5 4. . . . . . . . . . . . . . . . . . . . . . Hardenability . . . . . . . . . . . . . . . . . . . . . . . . . . Copper Base Gearing . . . . . . . . . . . . . .11 4. Metallurgical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flame and Induction Hardening . . . . . . .8 4. . . . . . . . . . . . . . . . Shot Peening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Heat Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 4. . . . . . . . . . .10 6. . . . . . . . . . . . . . . . . . . . 26 28 34 38 39 41 42 42 47 51 Metallurgical Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . .4 5. . . . . . . . . . . . . . . . . .7 4. . . . . . . . . . . . . . . . . . . . . . . . . . . .9 4. . . . . . . . . . Selection Criteria for Wrought. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 5. . . . . . . . . . . . . . . 52 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nitriding . . . . . . . . Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 Incoming Material Quality Control . . . . . . . . . . . . . . . . . . . . . Part Characteristics . . . . . . . . . . . Machinability . . . . . .6 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cost and Availability . . . . . . . . . . . . . . . . . . . 5 6 7 7 7 8 9 9 19 19 25 25 Heat Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 4. . . . . .9 5. . . . . . . . . . . Materials Selection Guidelines . . Definitions . . . . . . . . . . . . . . . . . . . . or Fabricated Steel Gearing . 1 2. . . . . . . . .6 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 5. . . . . . . . . . . . . . . . . . . . . . . . . .3 6. . . . . . . . . . . . . 1 Information Sources . . .1 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonitriding . . . . . . . . . . . . . .7 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical and Non---Destructive Tests and Inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 4. . . . . . . . . .8 5. . . . . . Through Hardening Processes . . . Scope . . . . . . . . . . . . . . . . . . . . . . . Residual Stress Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 4. . . 1 2. . . . . . . . . . References and Information . . . . . . . . . . . . . . Mechanical Property Test Bar Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 2. . . . . . . . . . . . .2 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 References . . . . . . . . . . . . . . . . . . . . 52 52 53 53 55 56 61 63 Bibliography . . . Non---Metallic Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grade and Heat Treatment . . . . . . . . 5 4. . . . . . . . . . . . . . . .7 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Incoming Material Hardness Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dimensional Stability . . . . . . . . . . . Incoming Material Mechanical Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microstructure . . . . . . . . . . . Other Non---Ferrous Materials . . Cast. . . . . . . .3 5. . . . . . . . . . . . . . . . . . . . . 2 4. . . . . . . . . . . . . . . . . . .6 5. . . . . Heat Treat Process Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 5. . . . . . . 64 ANSI/AGMA v 2004---B89 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carburizing . . . . . . . . . . Cleanliness . . . . . . . . . . . . . . . . . . . . . . . . . . . . Commonly Used Quenchants for Ferrous Gear Materials . . . . . . . . . Stress Relieved Steel Bars (Special Cold Drawn. . . . . . Chemical Analyses of Cast Bronze Alloys . . . . . . . . Mechanical Property Requirements --. . . . . . . . . 65 6 Table 4---6 Table 4---7 Table 4---8 Table 4---9 Table 4---10 Table 4---11 Table 4---12 Table 4---13 Typical Gear Materials --. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Gear Materials and Heat Treatment Manual Table of Contents Section Title Page Appendices Appendix A Appendix B Plastic Gear Materials . . . . . . . . Machinability of Common Gear Materials . . . . . . . . . . . . . . . . . . . . . Approximate Maximum Controlling Section Size Considerations for Through Hardened Gearing . Typical Shot Size and Intensity for Shot Peening . . . . . . . . . . . . . . . . . . . Approximate Minimum Core Hardness of Carburized Gear Teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tensile Properties of Through Hardened Cast Steel Gears . . . . . . . . . . . . . . Typical Chemical Analyses for Though Hardened Cast Steel Gears . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Effective Case Depth Specifications for Carburized Gearing . . . . . . . . . . . . 35 38 39 41 43 50 Appendix C Appendix D 67 69 70 Tables Table 4---1 Table 4---2 Table 4---3 Table 4---4 Table 4---5 ANSI/AGMA vi 7 8 10 2004---B89 . . . . . .Nitrided Steels . . . . High Tensile) . . . . . . . .Wrought Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Cold Drawn. . Typical Brinell Hardness Ranges and Strengths for Annealed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Properties of Cast Bronze Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Properties of Ductile Iron . . . . . . . . . . . . . . . Chemical Analyses of Wrought Bronze Alloys . . . . Approximate Minimum Surface Hardness --. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Brinell Hardness Ranges and Strengths for Quenched and Tempered Steel Gearing . . . . . Normalized & Tempered Steel Gearing . . . . . . . . . . . . . . . . . . . . . . . Service Life Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 14 14 16 17 22 22 23 24 Table 5---1 Table 5---2 Table 5---3 Table 5---4 Table 5---5 Table 5---6 Test Bar Size for Core Hardness Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Mechanical Properties of Wrought Bronze Alloy Rod and Bar . . . . . . Minimum Hardness and Tensile Strength Requirements for Gray Cast Iron . . . . . . . . . . . . . . . Case Hardenability of Carburizing Steels . . . . . . . . . . . . . . . . . . . . . . . . 58 59 61 62 Fig 5---2 Fig 5---3 ANSI/AGMA vii 29 30 2004---B89 . . . .Gear Materials and Heat Treatment Manual Table of Contents Section Title Page Figures Fig 4---1 Fig 4---2 Typical Design of Cast Steel Gears . . . . . . . . . . . . . . . . . . . . . . . . 33 45 46 48 49 50 Fig 6---1 Fig 6---2 Fig 6---3 Fig 6---4 Circular (Head Shot) Magnetic Particle Inspection . . . . . . . . Typical Distortion Characteristics of Carburized Gearing . . . . . . . . . . . . . 20 Fig 5---1 Fig 5---4 Fig 5---5 Fig 5---6 Fig 5---7 Fig 5---8 Variation in Hardening Patterns Obtainable on Gear Teeth by Flame Hardening . . . . . . . . . . Depth of Compressive Stress Versus Almen Intensity for Steel . . . . . . Variations in Hardening Patterns Obtainable on Gear Teeth by Induction Hardening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recommended Maximum Surface Hardness and Effective Case Depth Hardness Versus Percent Carbon for Flame and Induction Hardening . . . . . Coil Shot Magnetic Particle Inspection . . . . . . . . . . . . . . . . . . . Distance---Amplitude Reference Line for Ultrasonic Inspection . . . . . . . . . . . . . . . . . Shot Peening Intensity Control . . . . . . . . . . . . . . . . . . . . . . . Ultrasonic Inspection Oscilloscope Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Design Guidelines for Blanks for Carburized Gearing . . . . . . . . . . . . . . . . . . . . . . . . 13 Directionality of Forging Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Residual Stress by Peening 1045 Steel at 62 HRC with 330 Shot . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gear Materials and Heat Treatment Manual (This page is intentionally left blank) ANSI/AGMA viii 2004---B89 . Recommended Practice by American Society for Nondestructive Testing ASTM E54---80. ASTM A311---79. Test Method for Brinell Hardness of Metallic Materials ANSI/AGMA 6034---A88. Recommended Practice for Ultrasonic Examination of Heavy Steel Forgings 2. Low Alloy. All publications are subject to revision. ASTM A400---69(1982). Standard Specification for Carburizing Steels for Anti---Friction Bearings ASTM A535---85. Society of Automotive Engineers. Methods of Tension Testing of Metallic Materials AGMA 6033---A88. Method for End---Quench Test for Hardenability of Steel ANSI/AGMA SAE J462---Sept 81. are covered in AGMA rating standards. and Stainless Steel Castings for Steam Turbines ASTM A370---77. SAE. Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials ASNT---TC---1A (June 80). Wrought and Cast Copper Alloys ASTM A255---67. Cast Copper Alloys 1 2004---B89 . the editions were valid. and the users of this Standard are encouraged to investigate the possibility of applying the most recent editions of the publications listed. Carbon and Low Alloy Ultrasonic Examinations Thereof AGMA 141. but. Part 1 Materials ASTM E10---78. Specification for Gear Bronze Alloy Castings AGMA 2001---B88. Automotive Ductile (Nodular) Iron Castings ASTM A148---84. Heavy---Walled Carbon. Specification for Pearlitic Malleable Iron Castings SAE J461---Sept 81. Specification for Stress Relieved Cold Drawn Carbon Steel Bars Subject to Mechanical Property Requirements Metallurgical aspects of gearing as related to rating (allowable sac and sat values) are not included. ASTM A536---80. their treatments. Specification for Gray Iron Castings ASTM E112---84. Practice for Single and Double Reduction Cylindrical ---Worm and Helical --Worm Speed Reducers ASTM E18---79. constitute provisions of this document. Carbon and Alloy Steel Forgings for Rings for Reduction Gears ASTM A310---77. Methods and Definitions for Mechanical Testing of Steel Products This Manual was developed to provide basic information and recommend sources of additional information pertaining to gear materials. A Report on the State of the Art ASTM B427---82. Scope ASTM A290---82.01---1984. ASTM. Standard Specification for Special ---Quality Ball and Roller Bearing Steel The following documents contain provisions which. Standard for Marine Propulsion Gear Units. Plastics Gearing --Molded. American Society of Nondestructive Testing. Method for Chemical Analysis of Special Brasses and Bronzes ASTM A48---83. for Structural Purposes ASTM A220---76. American Gear Manufacturers Association. The abbreviations include: AGMA. American Society for Testing Materials. through reference in this Standard. References and Information ASTM 388---80.1 References. High Strength. And Other Methods. Specification for Ductile Iron Castings ASTM A833---84. At the time of publication. Fundamental Rating Factors and Calculation Methods for Involute Spur and Helical Gear Teeth ASTM B505---84. ASNT. Methods for Determining Average Grain Size SAE J434---June 86. ASTM A356---84. Indentation Hardness of Metallic Materials by Comparison Hardness Testers ASTM A609---83. Abbreviations are used in the references to specific documents in this Standard. Specification for Copper---Base Alloy Continuous Castings ASTM E8---83. Steel Castings. Methods and Definitions for Mechanical Testing of Steel Products 2. and other considerations related to the manufacture and use of gearing. Machined.Gear Materials and Heat Treatment Manual 1. Specification for Steel Castings. Recommended Practice for Selection of Steel Bar Compositions According to Section ASTM A534---87. This treatment forms coarse lamellar pearlite. This heat treatment results in the best machinability for high carbon (0. Spheroidize annealing is a process of heating and cooling steel that produces a globular carbide in a ferritic matrix. Full annealing consists of heating steel or other ferrous alloys to 1475---1650_F (802---899_C) and furnace cooling to a prescribed temperature. Austempering is applied to steels and. Requirements for Nondestructive Testing Methods ASTM E709---80. some of whom are: ASM International ASM Metals Handbooks ASM Heat Treaters Guide ASM Metals Reference Book ASM Standard ANSI/AGMA 2 2004---B89 . Design of gears is concerned with the selection of materials and metallurgical processing. Material specifications are issued by agencies. Austempering is a heat treat process consisting of quenching a ferrous alloy (steel or ductile iron) from a temperature above the transformation range in a medium having a rate of cooling sufficiently high to prevent high temperature transformation products. This Manual cannot substitute for metallurgical expertise. Shot Peening of Metal Parts MIL---STD---271F.8. annealing is assumed to mean full annealing. Test Method for Plain ---Strain Fracture Toughness of Metallic Materials Annealing --. Standard Reference Radiographs for Steel Castings Up to 2 inch (51 mm) in Thickness ANSI/SAE AMS 2300 F. Austempering. Inc.2 Information Sources.60 percent carbon or higher) and alloy steels. generally below 600_F (316_C). Standard Reference Radiographs for Heavy Walled (4 1/2 to 12 inch)(114 to 305 mm) Steel Castings 3. large industrial users.Spheroidizing.3). Aircraft ---Quality Steel Cleanliness 2. The material information and metallurgical processes contained herein are based on established data and practices which can be found in the appropriate publications. Premium Aircraft ---Quality Steel Cleanliness ANSI/SAE AMS 3201 G. It is necessary that the designer use a source of metallurgical knowledge of materials and processing. and technical societies. Standard Reference Radiographs for Heavy Walled (2 to 4 1/2 inch)(51 to 114 mm) Steel Castings ASTM E280---81. Wrought Copper and Copper Alloys American Society for Testing and Materials ASTM Standards Society of Automotive Engineers. but is intended to be a basic tool to assist in the selection and metallurgical processing of gear materials. Manual on Shot Peening MIL---S---13165 B (31 Dec 66 Amendment 2---25 June 79). Definitions ASTM E399---83. but above the martensitic range. Reference Photographs for Magnetic Particle Indications on Ferrous Castings ASTM E186---8. Austenite in ferrous alloys is a microstructural phase consisting of a solid solution of carbon and alloying elements in face---centered cubic crystal structured iron. Annealing --. Magnetic Particle Inspection. more recently in the development stage for ductile iron gearing (refer to 4. Magnetic Particle Examination ASTM E125. Austenite. Magnetic Particle Inspection. and maintaining the alloy temperature within the bainitic range until desired transformation is obtained. Unless otherwise stated. SAE Handbook American Iron and Steel Institute AISI Steel Products Manuals American National Standards Institute ANSI Standards Naval Publications and Forms Center Military Standards and Specifications Metal Powder Industries Federation MPIF Standard 35 Copper Development Association CDA Data books Iron Castings Society Gray and Ductile Iron Castings Handbook Steel Founders’ Society Steel Castings Handbook SAE J808a---SAE HS 84. the best microstructure for machinability of low and medium carbon steels. ASTM E446---81.Full.Gear Materials and Heat Treatment Manual SAE J463---Sept 81. including the government.4. The bainitic transformation range is below the pearlitic range. 40 percent carbon. Generally as carbon is increased.40 percent carbon. Cementite is a hard microstructure phase otherwise known as iron carbide (Fe3C) and characterized by an orthorhombic crystal structure. Etched case depth is determined by etching a sample cross---section with nitric acid. which results in the formation of complex nitrides in a high carbon case. tensile strength and wear resistance increase. which results in the diffusion of carbon into the part (0.004 inches (0. Its appearance is feathery if formed in the upper portion of the bainite transformation range. Case Hardness. Carburized case depth terms are defined as follows: Combined Carbon. Case Hardness is the micro--hardness measured perpendicular to the tooth surface at a depth of 0. A modified form of gas carburizing. This is defined as the depth at which the hardness is 10 HRC points below the minimum specified surface hardness. Core Hardness. (Ideal Critical Diameter). Estimating based on microstructure ignores the hardenability of the base material and is not as accurate a measurement as directly analyzing the carbon level. and acicular if formed in the lower portion.00 percent carbon is typically obtained at the surface). The temperature at which ferrous alloys undergo a complete microstructural phase transformation to austenite. Core Hardness for AGMA tooth design purposes is the hardness at the intersection of the root diameter and the centerline of the tooth at mid face width on a finished gear. parts are either cooled to 1475---1550_F (802---843_C) and held at this temperature to stabilize and then direct quenched. Carbon. The case depth for carburized gearing may be defined in several ways including effective case depth.30 percent carbon) at 1650---1800_F (899---982_C) in a controlled carbonaceous atmosphere. and depth to 0.5 tooth height and mid face width.Gas.I. Case Depth of Flame or Induction Harden Components. 3 2004---B89 . The total case depth is the depth to which the carbon level of the case has decreased to the carbon level of the base material. D. total case depth. or slow cooled and reheated to 1475---1550_F (802---843_C) and quenched. (1) Effective case depth. This depth may be measured by analyzing the carbon content or estimating based on microstructure. Nitrided case depth is defined as the depth at which the hardness is equivalent to 105 percent of the measured core hardness. Ideal critical diameter is the diameter which.002 to 0. Bainite. (4) Case depth to 0. Carbonitriding. After carburizing. Gas carburizing consists of heating and holding low carbon or alloy steel (less than 0. This results in simultaneous absorption of carbon and nitrogen. normal to the tooth surface.5 tooth height and mid face width. in which steel (typically plain carbon and very low alloy) is heated between 1450---1650_F (788---899_C) in an ammonia enriched carburizing atmosphere. Temperatures above 1800_F (982_C) may be ultilized in specialized equipment such as vacuum carburizers. Effective case depth is less frequently referred to as the depth to 0.5 times the effective case depth. The case depth is determined by a microhardness tester and measured normal to the tooth surface at 0. The amount of carbon in steel or cast iron that is present in other than elemental form. Carburizing--. (3) Total case depth.5 tooth height and mid face width. (2) Etched case depth. and measuring the depth of the darkened area. ductility and weldability decrease.40 percent carbon. The effective case depth is the hardened depth to HRC 50 at 0. Decarburization is the reduction in surface carbon content of a gear or test piece during thermal processing. Hardness survey is preferred for contral purposes. Carbon is the principal hardening element in steel. etched case depth. however. Case Depth of Nitrided Components. The etched case approximates the effective ANSI/AGMA Decarburization. will result in a microstructure consisting of 50 percent martensite of the center of the bar. The carburized case depth referred to in this Manual will be effective case depth. Cementite.10 mm) at 0. Bainite is a microstructural phase resulting from the transformation of austenite. and it’s amount determines the maximum hardness obtainable.Gear Materials and Heat Treatment Manual Austenitizing Temperature. when quenched in an infinite quench severity (such as ice brine). and consists of an aggregate of ferrite and iron carbide. Case Depth of Carburized Components. This is approximately 1. case. There is poor correlation between microstructure readings and material strength gradients using this method.05 to 0.70---1. Ferrite is a microstructural phase consisting of essentially pure iron. is subjected to a cracked ammonia furnace atmosphere at 950---1060_F (510---571_C) causing nitrogen to be absorbed into the surface. or other fabricating techniques. a superficial test must be used. cooling the specimen to room temperature. This term includes a number of heat treat processes in which nitrogen and carbon in varying concentrations are abANSI/AGMA 4 2004---B89 . welding. and viewed at 100X or higher magnification. Nitrocarburizing is done mainly for antiscuffing and to improve surface fatigue properties. generally below 1275_F (690_C) to reduce hardness and increase toughness. Induction Hardening.Band Steels. Hardenability. Microstructure is the material structure observed on a sample polished to a mirror finish. To obtain accurate results on shallow case hardened parts.6 mm) intervals starting at the quenched end. Normalizing. Graphite. characterized by an acicular needle---like appearance. H---Band steels are steels which are produced and purchased to a specified Jominy hardenability range. Stress Relief. or spheroid. cold working. Stress relief is a thermal cycle used to relieve residual stresses created by prior heat treatments. forming hard iron nitrides. Nitriding (Gas). Flame Hardening of steel gearing involves oxyfuel burner heating to 1450---1650_F (788---899_C) followed by quenching and tempering. Flame Hardening.6). followed by rapid cooling (quenching). Surface Hardness. Martensite. Martensite is the diffussionless transformation of austenite to a body centered tetragonal structure. and is characterized with a body centered cubic structure. The test consists of heating a standard one inch (25 mm) diameter test bar to a specified temperature. Pearlite is a microstructure consisting of lamellar layers of ferrite and cementite. The part is then reheated (tempered) to a specific temperature generally below 1275_F (690_C) to achieve the desired mechanical properties for the gear application. The standard method for determining the hardenability of steel. after machining following quench and tempering. H--. Grain size is specified as either coarse (grain size 1 through 4) or fine (grain size 5 through 8). machining. Maximum stress relief is achieved at 1100_F (593_C) minimum. followed by quenching and tempering. Tempering. Normalizing is used primarily to obtain a uniform microstructure. These processes are used mainly for improved wear resistance and fatigue strength. Graphite is carbon in the free state with a shape described as either flake. placing the specimen in a fixture so that a stream of water impinges on one end. Nitriding (Aerated Salt Bath). Nitrocarburizing is a gaseous heat treatment in which both nitrogen and carbon are absorbed into the surface of a ferrous material at a temperature below the austenitizing temperature [1000---1150_F (538---621_C)]. etched. An indication of the depth to which a steel will harden during heat treatment (see 4. Hardening. or malleable. Microstructure. Normalizing consists of heating steel or other ferrous alloys to 1600---1800_F (871---982_C) and cooling in still or circulated air. Quench and Temper. and measuring the hardness at 1/16 inch (1. determined according to ASTM E112. The quench and temper process on ferrous alloys involves heating a part to the austenite transformation state at 1475---1650_F (802---899_C). Induction hardening of gearing is the selective heating of gear teeth profiles to 1450---1650_F (788---899_C) by electrical inductance through the use of a coil or single tooth inductor to obtain the proper heat pattern and temperature. sorbed into the surface of a ferrous material at a temperature below the austenitizing temperature [1000---1150_F (538---621_C)]. The process of increasing hardness. while submerged in a gas stirred and activated molten chemical salt bath.Gear Materials and Heat Treatment Manual Ferrite (alpha). Surface hardening process in which alloy steel. Pearlite. ductile. Nitrocarburizing. nodule. grinding flats. Surface Hardness is the hardness measured directly on the surface. The graphite shape classifies the type of cast iron as either gray. typically through heating and cooling. with a body centered cubic crystal structure. Grain Size. Tempering is reheating a hardened part to a specified temperature. Jominy End Quenching Hardenability Test. 7 Stock Removal. Round and flat stock can be purchased in numerous combinations of mechanical and thermal processing. Material Selection Guidelines Many factors influence the selection of materials for gears. 4. Transformation Temperature. stress relieved. such as hot rolled. toughness may be important for high impact or low temperature applications or both. at a given stress level. normalizing (or normalizing and tempering) and quenching and tempering (refer to 5. miANSI/AGMA 5 2004---B89 . pickled. Most wrought ferrous materials used in gearing are heat treated to meet hardness and/or mechanical property requirements.1 Hardness.Gear Materials and Heat Treatment Manual crostructure. 4.6 Heat Treatment. Gear blanks are generally given an annealing or normalizing heat treatment. Tensile strength predicts the stress level above which fracture occurs.1. which act as stress concentrators). cold rolled.structure for machinability and mechanical property uniformity. Through hardening is a term used to collectively describe methods of heat treatment of steel other than surface hardening techniques. Core hardness is an important consideration for bending and impact strength. 4. Contact and bending fatigue strengths are used to predict.2 Fatigue Strength. nonmetallic inclusions. These factors include: (1) (2) (3) (4) (5) (6) (7) Mechanical Properties Grade and Heat Treatment Cleanliness Dimensional Stablility Availability and Cost Hardenability and Size Effects Machinability and Other Manufacturing Characteristics 4. 4. A test coupon is an appropriately sized sample(often a bar) used generally for surface hardening treatments. annealed. Surface hardness is an important consideration for gear wear. Through Hardening. section size and heat treat considerations. The minimum surface stock removal varies with stock size and type of mechanical working. and the relative importance of each can vary.1. This layer should be removed from critical gearing surfaces.1 Mechanical Properties.. The test coupon should be heat treated along with the gear(s) it represents. material cleanliness.3 Tensile Strength.1. The temperature at which a change in microstructure phase occurs. surface conditions and residual stresses. with regard to composition and hardenability limits. Although not directly considered in gear rating. Toughness of steel gearing is adversely affected by a variety of factors such as: NOTE: Through hardening does not imply that the part has equivalent hardness throughout the entire cross section. etc. as the gear it represents. 4. It is necessary for the gear designer to know the application and design loads and to calculate the stresses before the material selection can begin.1. material defects. seams. (1) Low temperature (2) Improper heat treatment or microstruc--ture (3) High sulfur (4) High phosphorus and embrittling type residual elements (5) Nonmetallic inclusions (6) Large grain size (7) Absence of alloying elements such as nickel. NOTE: Gear toughness is adversely affected by design or manufacturing considerations (such as notches. tensile ductility and/or fracture toughness testing.1.1. tool marks. Test Coupon. It is not recommended for use in gear manufacturing specifications. Gear blanks can also be quenched and tempered. All rough ferrous gear castings.4 Yield Strength. 4. which homogenizes the micro--. Toughness is determined by impact strength. Contact and bending fatigue strengths are influenced by a variety of factors such as hardness. Depth of hardening is dependent upon hardenability. the number of cycles that gearing can be expected to endure before pitting or fracture occurs.1).1. which is used in AGMA gear rating practice.5 Toughness. The strength properties are closely related to material hardness. cold drawn. 4. It should be of the same specified material grade. Minimum 4. These include: annealing. and other surface imperfections. small fillet radii. Yield strength determines the stress level above which permanent deformation occurs. and quenched and tempered. forgings and barstock have a surface layer containing decarburization. I---H. T---H&N. I---H. F---H Low Hardenability Marginal Hardenability Fair Hardenability Medium Hardenability Medium Hardenability Good Hardenability in Heavy Sections Nitralloy 135 Mod. ANSI/AGMA 6 2004---B89 . I---H. I---H.Wrought Steel Common Alloy Steel Grades Common Heat 1 Treat Practice General Remarks/Application 1045 4130 4140 4145 8640 4340 T---H. 4. I---H. quired as a function of subsequent heat treatment. Excellent Hardenability in Heavy Sections 1020 C---H Very Low Hardenability 4118 4620 8620 C---H C---H C---H Fair Core Hardenability Good Case Hardenability Fair Core Hardenability 4320 8822 C---H C---H Good Core Hardenability Good Core Hardenability in Heavy Sections 3310 @ 4820 9310 C---H C---H C---H Excellent Hardenability (in Heavy Sections) for all three grades 1 C---H = Carburize Harden T---H = Through Harden F---H = Flame Harden I---H = Induction Harden T---H&N = Through Harden then nitride 2 Recognized. T---H&N. F---H T---H. 4---2. such as quench and temper or case hardening. F---H T---H. Nitralloy G 4150 T---H&N T---H&N I---H. I---H. See Tables 4---1. TH&N 4142 I---H. T---H.Gear Materials and Heat Treatment Manual stock removal tables can be found in most machining and materials handbooks. The specific gear design will usually dictate the grade of material re- Table 4---1 Typical Gear Materials --. T---H&N 4350 @ T---H. F---H T---H T---H. and 4---3 for grades and recommended heat treatments. but not current standard grade. F---H. F---H. T---H&N. F---H Special Heat Treatment Special Heat Treatment Quench Crack Sensitive Good Hardenability Used when 4140 exhibits Marginal Hardenability Quench Crack Sensitive. F---H T---H. T---H&N.2 Grade and Heat Treatment. Improved cleanliness (reduced nonmetallic inclusion content) results in improved transverse ductility and impact strength. Steels shown in order of increased hardenability. Hardening by quench and tempering results in a combination of properties generally superior to that achieved by anneal or normalize and temper. inert atmosphere (argon) shielded and bottom poured to improve cleanliness and reduce objectionable gas content (hydrogen.Gear Materials and Heat Treatment Manual Table 4---2 Typical Brinell Hardness Ranges and Strengths for Annealed. must be fully evaluated with respect to the need for improved properties for other than critical gearing applications.. Normalized and Tempered Steel Gearing Normalized & Tempered # Annealed Heat Treatment @ Typical Alloy Steels 1 Specified 1045 4130 8630 4140 4142 8640 4145 4150 4340 4350 Type Brinell Hardness Range HB Tensile Strength min ksi (MPa) Yield Strength min ksi (MPa) Brinell Hardness Range HB Tensile Strength min ksi (MPa) Yield Strength min ksi (MPa) 159---201 80 (550) 50 (345) 159---201 80 (550) 50 (345) 156---197 80 (550) 50 (345) 167---212 90 (620) 60 (415) 187---229 95 (655) 60 (415) 262---302 130 (895) 85 (585) 197---241 100 (690) 60 (415) 285---331 140 (965) 90 (620) 212---255 110 (760) 65 (450) 302---341 150 (1035) 95 (655) 1. etc. oxygen and nitrogen). Significant ANSI/AGMA NOTE: For more information see ASTM A534 and A535. with sulfur content less than 0. Alloy steel manufactured with electric furnace practice for barstock and forged steel gear applications is commonly vacuum degassed. ductility. etc.e. See Table 4---3 for quench and tempered gearing. to minimize distortion and possible cracking (see 5. impact. but machinability may be reduced. Hardness and strengths able to be obtained by normalize and tempering are also a function of controlling section size and tempering temperature considerations. 2. 4.3 Cleanliness. restricted hardenability. die steps. Vacuum degassed steel may be further refined by vacuum arc remelting (VAR) or electroslag remelting (ESR) of the steel. for example.8). These refining processes further reduce gas and inclusion size and content for improved fatigue strength to produce the highest quality steel for critical gearing applications. 3. 7 2004---B89 .5 Cost and Availability. increase in cost and reduced machinability. i. and AMS 2301 and 2300. The process to achieve the blueprint design may require material considerations such as: added stock. 4. 4. The specific material selection is often determined by cost and availability factors such as standard industry alloys and procurement time.015 percent. however.4 Dimensional Stability. [ Hardness range is dependent upon controlling section size (refer to appendix B) and quench severity. the mill quantity cost may be substantially lower. 8620. 4140. Hardenability is normally determined by the Jominy End Quench Test (ASTM A255) or can be predicted by the Ideal Diameter (DI) concept. 4.6 Hardenability. In the case of steel and iron castings and nonferrous materials. ] It is difficult to cut teeth in 4100 Series steels above 341 HB and 4300 Series steels above 375 HB. which is largely determined by the alloy content of the steel grade. by quenching from the austenitizing temperature.1. The standard wrought carbon and alloy steels such as 1020. When specifying parts with small quantity requirements. The depth to which a particular hardness is achieved with a given quenching condition is a function of the hardenability. and non---standard steels can be supplied on special request.6. 4.Gear Materials and Heat Treatment Manual Table 4---3 Typical Brinell Hardness Ranges and Strengths for Quenched and Tempered Alloy Steel Gearing Alloy Steel * Grade 4130 8630 4140 8640 4142 4145 4150 4340 4350 Tensile Strength minimum ksi (MPa) Yield Strength minimum ksi (MPa) Heat Treatment Hardness Range HB [ Water Quench & Temper 212---248 up to 302---341 100 (690) 75 (515) 145 (1000) 125 (860) Oil Quench & Temper 241---285] up to 341---388 120 (830) 95 (655) 341---388 170 (1170) 277---321 up to 363---415w 135 (930) 180 (1240) Oil Quench & Temper 150 (1035) 110 (760) 145 (1000) * Steels shown in order of increased hardenability. 4320. 4150 and 4340 are available from service centers and steel mills. Steel mill purchases require “mill quantities” (several thousand pounds) and long delivery time. Hardenability of steel is the property that determines the hardness gradient produced ANSI/AGMA 8 2004---B89 . The bar is placed in a fixture. The as quenched surface hardness is dependent primarily on the carbon content of the steel part and cooling rate. four inches (102 mm) in length is first normalized then uniformily heated to a standard austenitizing temperature.1 Determination.1 Jominy Test Method. but costs should be evaluated due to reduced machinability.6. 4. However. 9310. 4820. then quenched by spraying room temperature water against one end face. A one inch (25 mm) diameter bar. (4340 and 4350 provide advantage due to higher tempering temperatures and microstructure considerations) w High specified hardness is used for special gearing. Service centers can usually furnish these materials in small quantities and with short delivery time from their inventories. These steels can be ordered to “H” Band hardenability ranges. SAE and ASTM designations should be used wherever possible. 4350 being the highest. standard alloys should be specified or engineering drawings should allow optional materials. Chemical composition and microstructure of steel have major influences on machinability. and poor machinability. may significantly reduce fatigue life compared to conventional steelmaking practices. The standard wrought steel forms are round stock. The Ideal Critical Diameter Method (DI) is based on chemical analysis described in AISI.7 Machinability. (2) Cutting speeds.2 Application.1.1. particularly in the transverse direction. and tellurium form soft inclusions in the steel matrix and can benefit machining. availability. and quenching conditions. Dependent on carbon and sulfur levels.Gear Materials and Heat Treatment Manual 4.Band Steel. sulfur. flat stock and forgings.6. irregular inclusions and can also benefit machining. The more common gear materials are listed in Table 4---4 on the basis of good. Jominy hardenability is expressed in HRC obtained at each interval starting at the water quenched end face.6 mm) intervals. However. 4. configuration. These Bands are published by ASTM. Several factors influence the machinability of materials and in turn affect the economy and feasibility of manufacturing. quantity. Modern Steels and Their Properties by Bethlehem Steel. AISI.8. etc. particularly when high strength levels are being specified.6. 4. There is abundant material published on machinability. cast iron and ductile irons.4 Ideal Critical Diameter. fair. These forms include wrought steel. precision. feeds and cutting tools. and economic considerations. Example: J5 = 40 is interpreted as a hardness of 40 HRC at a distance of 5/16 inch (8 mm) from the water quenched end. With good machinability as a base.3 H--. specifications. quench media. ANSI/AGMA 4. Jominy hardenability has been applied to standard steels. including rigidity. size. Steels can be purchased to H---Band. and other hardenability reference publications. Calcium treated steel. These factors must be considered at the design stage. since they affect properties and structures. and are available in a wide range of sizes and grades.8 Ferrous Gearing. Rockwell C hardness measurements are made along the length of the bar on ground flats in one sixteenth of an inch (1. design. and poor would add 40 to 50 percent. lead and calcium inclusions which improve machinability can decrease mechanical properties.6. part size. Ferrous materials for gearing include carbon and alloy wrought and cast steels. 9 2004---B89 . hardness will vary with the cooling rate. SAE. and size. 4. Hardenability is constant for a given steel composition.6. microstructure.1 Wrought Steel. power. shape. As the section thickness increases. and SAE. the hardness obtained at any location on a part will depend on carbon content.1.30 percent decreases machinability due to increased hardness. Metallic oxides like alumina and silica form hard oxide inclusions and contribute to poor machinability.2 Jominy Analysis. For a given composition the Jominy hardenability data falls within a predicted range. or restricted H---Band. Typically a steel composition is selected with a hardenability characteristic that will yield an as quenched hardness above the specified hardness so that toughness and machinability can be attained through appropriate tempering. In general. Forgings reduce machining time. lead. Wrought steel is the generic term applied to carbon and alloy steels which are mechanically worked into form for specific applications. (4) Characteristics of the cutting fluid used. The mechanics of the cutting operation will not be considered here. the steel hardenability must be increased in order to maintain a given hardness in the part section. Gearing of alloy and carbon steel is manufactured from different forms of rough stock depending upon service. however. Only metallurgical factors will be discussed. including composition. Factors influencing machinability are: (1) Material being cut. alloys which increase hardness and toughness decrease machinability. higher manganese also decreases machinability. 4. Carbon content over 0. a fair rating would add 20 to 30 percent to the machining cost. 4. selenium. Steels purchased to predicted hardenability ranges are called H---Band steels. when used in high stress gear and shaft applications. Elements such as sulfur. Therefore. hardenability. Calcium additions (in steel making) form hard. weld fabrications and castings. hardness. (3) Condition of machine tools. The higher carbon level in 4145. 4150. as rolled. Inadequate (slack) quench with subsequent low tempering temperature may produce a part which meets the specified hardness. Inadequate cooling during normalizing can result in gummy material. if sulfur content is low. 3310 4320 4820 9310 Material Grades Fair to good machinability if normalized and tempered. reduced tool life and poor surface finish. the higher carbon results in lower machinability.Gear Materials and Heat Treatment Manual Table 4---4 Machinability of Common Gear Materials Material Grades Low--. machinability may decrease appreciably.Carbon Carburizing Steel Grades --. 4145 4150 4340 4345 4350 Remarks for medium carbon alloy steel (above) apply. or as forged. The very high strength heat treated bronzes [above 110 ksi (760 MPa) tensile strength] have fair machinability. 4118 4620 8620 8822 Good machinability. However. Ductile Irons Annealed or normalized ductile cast iron has good machinability. Because of work hardening tendencies. Higher strength gray cast irons [above 50 ksi (345 MPa) tensile strength] have reduced machinability. or normalized and tempered to approximately 255 HB or quenched and tempered to approximately 321 HB. normalized is preferred.Remarks Gray cast irons have good machinability. Austenitic Stainless Steel All austenitic stainless steel grades only have fair machinability. Above 352 HB. Over 321 HB. feeds and speeds must be selected to minimize work hardening. Above 363 HB. Quenched and tempered ductile iron has good machinability up to 285 HB and fair machinability up to 352 HB. machinability is fair. However.015 percent. gear steels are generally used in the fine grain condition since mechanical properties are improved. Normalizing without tempering results in reduced machinability. Inadequate (slack) quench can seriously affect machinability in these steels. but produces a mixed microstructure which results in poor machinability. machinability is poor. machinability is poor. and 4350 makes them more difficult to machine and should be specified only for heavy sections. Medium Carbon Through Hardened Steel Grades --. as forged. 4130 4140 4142 Good machinability if annealed. 4340 machinability is good up to 363 HB. Gear Bronzes and Brasses All gear bronzes and brass have good machinability. ANSI/AGMA 10 2004---B89 .Remarks 1020 Good machinability. less than 0. Quench and temper as a prior treatment can aid machinability.Remarks NOTE: Coarse grain steels are more machinable than fine grain. Material Grades Gray Irons Other Gear Material --. The economics of the pretreatments must be considered. 1045 1141 1541 Good machinability if normalized. However. and distortion during heat treatment is reduced. or normalized. The “as cast” (not heat treated) ductile iron has fair machinability. annealed or quenched and tempered. Increasingly cleaner steels are now also being specified for gearing. 4345. Sulfur additions aid the machinability of these grades. However. as rolled. not a requirement.0 inch (405 mm) Table 4---5 Mechanical Property Requirements --.0 inch (125 mm) 16.1.8. hot rolled---cold drawn.1) to 3. Additional requirements: Hardness Rockwell C 32.001 (76.000 (76) * Stress Relieved. 4145 SS not available above 3. min. High Tensile) Size included inch (mm) Steel Designation Mechanical Properties for Rounds.500 (89) 4145 SS] 150 (1035) 130 (895) 10 w 32 3.1 Round Stock.Gear Materials and Heat Treatment Manual are manufactured to a size larger than can be formed with rolling dies or rolls. Approximate maximum diameter of the various types of round stock.375 (10) to 3.001 (76. They are typically available as hot rolled. Round bars can be purchased in various diameters for standard carbon and alloy grades. NOTE: Some cold finish steel companies furnish many of the above steels under various trade names. ] Special steel. hot rolled---cold finished and forged rounds. ground and/or polished) for improved size control. Forged round bars can be purchased in a variety of heat treat conditions depending upon application.000 (102) 1045 SR 1141 SR 1144 SR 105 105 105 (725) (725) (725) 90 90 90 (620) (620) (620) 9 9 9 24 24 24 0. Rockwell C 30. [ Special steel.5 in (89 mm). w Typical value. min ksi (MPa) ksi (MPa) HRCw 1137 SR * 1045 SR 1141 SR 1144 SR 1144 SS[ 4145 SS] 95 115 115 115 140 150 (655) (795) (795) (795) (965) (1035) 90 100 100 100 125 130 (620) (690) (690) (690) (860) (895) 11 10 11 10 10 w 10 w 24 24 24 24 30 32 3.Cold Drawn. is as follows: Hot Rolled: Cold Drawn: Cold Finished: Forged Round: 8.5 in (64 mm). 4. straightened and stress relieved. Forged round bars are forged round under a press or hammer at the same approximate temperature as hot rolled bars (higher temperature for lower carbon content carbon or alloy steel) and Hot rolled bars are also now manufactured from continuous cast steel bar manufactured with continuous casters.0 inch (205 mm) 4. Hot rolled bars are mechanically worked at approximately 2100---2400_F (1150---1315_C) and may be subsequently annealed.0 inch (100 mm) 5. Stress Relieved Steel Bars (Special Cold Drawn. Squares and Hexagons Minimum Minimum Elongation in Nominal Tensile Strength Yield Strength 2 inches (50 mm) Hardness percent. Cold drawing produces a close tolerance bar with improved mechanical properties (higher hardness and yield strength). ANSI/AGMA 11 2004---B89 . Low to medium carbon steels are normally available as cold drawn bar for gearing. depending upon steel mill capacity. 1144 SS not available above 2. Additional requirements: Hardness. but show no improvement in mechanical properties over hot rolled or annealed bar. Continuous cast bar is subsequently hot rolled with sufficient reduction in cross sectional area (7 to 1 minimum) during hot deformation to produce densification and quality bar for many gearing applications. Hot rolled---cold finished bars are machined (turned. min.1) to 4. electric arc. 4. (3) Rolled Ring Forging. by the Forging Industry Association 4.0 inch (254 mm) outside diameter with a 2. a forged or cast hub and mild steel plate for the web or arm support sections. Bottom poured ingots are poured with a bottom ingate and runner which provides molten steel to the ingot mold. Steel Products Manual Forging Industry Handbook. or induction furnace (1) Open Die Forging. reference should be made to the following sources: American Society for Metals (ASM International). Flat stock is typically available in hot rolled or hot rolled and annealed conditions. which incorporate cast arms rather than the heavier solid web design used for smaller gears. formed plate or castings for the rim (tooth) section. and then is rotated 90 degrees and hot worked again.1. welded assemblies are furnace stress relieved at 950---1250_F (510---675_C) depending upon the previous tempering temperature used to obtain the specified hardness of the rim section. Forging stock is always fully killed steel to minimize the occurrence of fissures due to dissolved gases during the forging process. This method produces a closer toleranced piece. Split gears are cast in two or four segments. Bottom poured ingots show improved macro---cleanliness and ingot yield (more usable ingot metal after conventional cropping or removal of the top pipe cavity and bottom discard of top poured ingots). which develop high centrifugal stress at the center. deformation is done while the billet is at temperatures generally above 1900_F(1038_C).3 Cast Steels. This method produces a rough dimensioned piece by mechanical deformation between an upper and lower die (hammer and anvil) in an open frame press or hammer.8. Carbon and alloy steel castings are used for a wide variety of through hardened gearing and. (2) Closed Die Forging. ASTM A290 should be referenced for ring forgings for fabricated gears. After weld assembly. split hub. using appropriate preheat and postheat temperatures.8. Metal Handbooks American Iron and Steel Institute (AISI). The standard forging classifications are: 4. Large diameter rings are rolled on a roller press from circular billets containing a central hole.3. Commercial flat or plate steel of numerous carbon and alloy grades is available in standard thicknesses in a wide range of widths and lengths.Gear Materials and Heat Treatment Manual 4. manufactured by electric furnace practice using part or all of the cleanliness techniques discussed in 4. to a lesser degree.1. Alloy steel. for case hardened applications. greater than 30.2 Flat or Plate. An upset forging is produced when the billet is initially hot worked in one direction. much like steel castings are produced. ANSI/AGMA 12 2004---B89 . can result in improved transverse ductility and impact strength. or split hub and rim design.8. Larger gears are usually solid hub. from which blooms and billets are manufactured prior to forming forgings and barstock. For additional information on wrought steel manufacture and steel making refining practices. are now also bottom poured as well as conventional top poured. Cast steel is manufactured by the open hearth. Typically the process involves piercing a pancake---shaped billet with a mandrel and shaping the ring by a hammer action between the mandrel and the press anvil.1 Manufacture. Typically.8. Open die forgings may be specified to be upset forged to increase center densification. Weld fabricated gears generally consist of rolled or forged rings.8. Typical cast gear designs are shown in Fig 4---1.3 Forgings.000 feet/minute (152 m/sec) pitch line velocity. The upper and lower dies trap the steel billet in a closed (confined) cavity and the press action deforms the metal to fill the die cavity.0 inch (51 mm) face width for solid rim gears. Cast ingots. to split ring gears about 480 inch (12 192 mm) outside diameter with a 40 inch (1016 mm) face. 4. with possible cored holes in the web or flange for weight reduction. Forgings are made by hot mechanical deformation (working of a steel billet into a specific form) which densifies the structure. and may provide improved inclusion orientation. Still larger ring gears are solid or split ring design with bolt holes at the splits and on the inside diameter flange for gear assembly and mounting purposes. Smaller gears generally have a solid web and hub design. Upset forgings are often used for critical high speed gearing. The size of cast gearing varies from 10.2 Weld Fabrications.3. generally smaller than an open die forging. producing a more exact contoured forging. The rim or tooth section is heat treated to obtain specified hardness (mechanical properties) prior to weld assembly. This method produces a donut---shaped work piece. Gear Materials and Heat Treatment Manual melting processes. 8640. The material grades used for cast gearing are generally modifications (silicon. and sulfur levels of cast steel. SOLID WEB CORED WEB SMALLER GEARS SOLID RING SOLID HUB SPLIT RING SPLIT HUB SPLIT HUB AND RING LARGER GEARS INCLUDING OPEN GEARING (NOTE: Each design above can be made by forging or weld fabrication. 4140. Carburizing grades are usually 1020.) Fig 4---1 Typical Design of Cast Steel Gears ANSI/AGMA 13 2004---B89 .2 Material Grades of Cast Steel. etc) of standard AISI or SAE designations. 4135. Through hardened gearing applications generally use 1045. and 4340 Typical chemical analyses and tensile properties of through hardened cast steels are shown in Tables 4---6 and 4---7. respectively. phosphorus. 4. Secondary refining processes can be used for reducing the gas.3.8. care must be taken to ensure that the specified cast analysis for through hardened gearing has sufficient hardenability to obtain the specified minimum hardness. type steels. 8620 and 4320 types. 8630. As with wrought steel. using both acid or basic lined furnace steel making practices. 43 0.0 35.030 0.050 0. Source: AGMA 6033---A88.60 1. ladle refining or AOD (argon oxygen decarburization) processing are used.50 0.38---0.0 13.27---0.0 F G 321---363 331---375 145 (1000) 150 (1030) 120 (830) 125 (860) 8.--- 0.90 0. Aluminum content of 0. Source: AGMA 6033---A88.70---1.60---0.00 0.0 20.60 --.2 percent Offset ksi (MPa) Percent Minimum Elongation in 2 in (50 mm) Percent Minimum Reduction in Area A B C 223---269 241---285 262---311 100 (690) 110 (760) 118 (810) 75 (480) 80 (550) 90 (620) 15.00 0.30 GENERAL NOTES: 1.37---0.0 28.40---0. Part 1 Materials.90 0.30---0.060 0.0 AGMA@ 6033---A87 Class NOTES: 1.0 D E 285---331 302---352 130 (900) 140 (970) 100 (690) 115 (790) 10.025 percent maximum may be specified for low alloy cast steel (per ASTM A356) for ladle deoxidation to improve toughness.40 0.60 0. 6.60 --.00 0.20---0.040 0.65---2.15---0.00 0. lower phosphorus and sulfur contents to less than 0. Above tensile requirements for seven classes are modifications of three grades of ASTM A148 (Grades 105---85 through 150---135). Vanadium content of 0.38---0. Sulfur. type of heat treatment and controlling section size (hardenability) considerations.----. ANSI/AGMA 14 2004---B89 .040 0.60---0.70---1. Part 1 Materials. 3. max.06---0. depending upon specified hardness (mechanical properties). Table 4---7 Tensile Properties of Through Hardened Cast Steel Gears! Brinell Hardness Range Minimum Tensile Strength ksi (MPa) Minimum Yield Strength 0.0 11.Gear Materials and Heat Treatment Manual Table 4---6 Typical Chemical Analyses for Through Hardened Cast Steel Gears Alloy Percent for Cast Steel Types Element Carbon Manganese Phosphorus. 5.10 0.60---1.00 0. 4. 2.0 9. cleanliness and machinability. Other AISI Type and proprietary chemical analyses are used for carbon and low alloy cast gears according to ASTM A148 or customer specifications.70---0.43 0.70---1.37 0.----.040 0.70---1.90 0. Type designations indicate non---conformance to exact AISI analysis requirements.--0.80---1.60---0.030 0.0 24. Standard for Marine Propulsion Gear Units. Nickel Chromium Molybdenum 1045 Type 4140 Type 8630 Type 8642 Type 4340 Type 0. max. Standard for Marine Propulsion Gear Units.0 7. 2.40---0.030 0.040 0.25 0.10 percent may be specified for grain refinement.030 0.50 0.020 percent are commonly achieved. max.0 26. Silicon.90 0.60 0.0 31.00 0. When basic steel making practice.90 0.0 18.60---0.45 0. ANSI/AGMA 15 2004---B89 .4 Cast Iron.8. Cast irons for gears are made by the electric arc furnace.3.8. gas cutting. 4.3. (1) Material considerations. Standard Reference Radiographs for Steel Castings Up to 2 inch (51 mm) in Thickness 4. test locations. 4. chills. Heat treatable electrodes (4130. The family of cast irons is classified by the following categories. cupola. 4. Information is available in: ASM Handbook series.2 and 6. Repair welding of castings prior to heat treatment is routinely performed by the casting producer. Minor discontinuities in finish machined teeth. Recommended ASTM specifications for nondestructive inspection test procedures are: ASTM E709---80.3. (2) Heat Treating. is performed to evaluate internal integrity of the rim (tooth) section when specified.8. Stress relieving may be deemed necessary to hold close dimensional tolerances. if allowed after heat treatment. Ultrasonic Examination of Carbon and Low Alloy Steel Castings ASTM E186---80. localized preheat and post heat are recommended to avoid or minimize unfavorable residual tensile stress or high hardness in the heat affected zone. Standard Reference Radiographs for Heavy Walled [2 to 41/2 inch) (51 to 114 mm)] Steel Castings ASTM E280---81. holding at temperature up to one hour per inch of maximum section and furnace cooled to below 600_F (315_C). Nondestructive Inspection and Quality Control 4. whenever possible. Approval by the customer may be required. Reference should be made to 6. Refer to Gray and Ductile Iron Castings Handbook for additional information. Casting should also be free of cracks. Gray iron contains (typically over 3. Cast Iron is the generic term for the family of high carbon. It is characterized by the gray color occurring on a fracture surface. Castings are heat treated to either a specified hardness or to specified hardness and minimum mechanical properties. are often contour ground for removal. It is recommended that castings be heated to 1000 to 1100_F (538---593_C). iron alloys. 8th edition. The minimum number of hardness tests required on both rim faces of gear castings is generally based on the outside diameter. shall be followed by reheat treatment.6 Additional Information for Cast Steel. The quality specified in other than the rim (tooth) section is often less stringent. If reheat treatment is not possible.3. Steel Founder’s Society of America (SFSA) Publication ASM Handbook. Castings must meet the nondestructive test requirements in the rim section. All welds should be inspected to the same quality standard used to inspect the casting. Standard Reference Radiographs for Heavy Walled [4 1/2 to 12 inch(114 to 305 mm)] Steel Castings ASTM E446---81. and unfused chaplets in the rim section. which is present as graphite flakes. Other nondestructive testing.8. Repair welds in areas to be machined should have machinability equivalent to the casting.4 Heat Treatment of Cast Steel. or induction practice and should be free of shrink. entrapped sand and hard areas in the tooth portion. silicon. in preference to cosmetic weld repair. Castings should be furnished free of sand. if present.8. such as radiograph and ultrasonic inspection. hot tears.Gear Materials and Heat Treatment Manual 4. and acceptance standards are established between the purchaser and manufacturer. Methods of testing.4. Reference Photographs for Magnetic Particle Indications on Ferrous Castings ASTM A609---83.3 for additional information. Repairs in the rim (tooth) portion and other critical load bearing locations should be performed only prior to heat treatment. scale. extraneous appendages. Magnetic Particle Examination ASTM E125---63 (1980). 8th edition.5 Quality of Cast Steel. Dry or wet fluorescent magnetic particle inspections are routinely performed to meet specified surface quality requirements. Repair welds in the tooth portion should only be performed with the approval of the gear purchaser. gas holes. porosity. Volume 11. Cast iron castings are generally furnished as cast unless otherwise specified. and repair welding which could adversely affect machining.0 percent) carbon. 4140 and 4340 Types) should be used for repairing prior to heat treatment in order to produce hardness equivalent to the base metal after heat treatment. Repair welding. NOTE: Weld repair in the tooth portion may require notification of the purchaser. and hard areas resulting from arc---airing. Volume 5. Mechanical property tests (tensile and impact) are generally required only when specified.3 Repair Welding of Cast Steel.1 Gray Iron. The number of tests increases with OD size.8. and sufficient hardness tests should be made to verify that the part meets the minimum hardness specified. Repair welds in areas to be machined should have equivalent machinability as the casting. porosity. Unless otherwise specified. Tensile test coupons should be poured from the same ladle or heat and be given the same heat treatments as the castings they represent.01---2 incl. Other properties may be as agreed upon by the gear manufacturer and casting producer. Hardness tests should be made in accordance with ASTM E10. A B C NOTE: See ASTM A48 for tolerances on as cast and machined diameter and retest considerations if bar fails to meet requirements. pearlitic or martensitic structures.51---1. Specified minimum hardness must be maintained to the finish machined dimensions for acceptance. (2) Heat Treating.2 Ductile Iron. is characterized by the spheroidal shape of the graphite in the metal matrix.20 (30. ASTM A48 Test Bar.7) 0. The size of the cast test coupon is dependent upon the thickness of the tooth portion of the casting as follows: 0. Repair welding in the tooth portion should only be performed with the approval of the gear purchaser.5---50. A wide range of mechanical properties are produced through control of the alloying elements and subsequent heat treatments. produced by innoculation with magnesium and rare earth elements. (Refer to Gray and Ductile Iron Handbook.8) (3) Chemical Analysis.) (1) Material Considerations. Typical mechanical properties are shown in Table 4---9.25 (31.Gear Materials and Heat Treatment Manual (3) Chemical Analysis. Unless otherwise specified. Size of the Y---block mold. Minimum hardness requirements for the classes of cast iron are shown in Table 4---8.25---0. (25.7) 0. in (mm) in (mm) 0. in (mm) Brinell Hardness 16 2004---B89 .00 (50.4. gas holes and entrapped sand and hard areas in the tooth portion. if used. normalizing and tempering or quenching and tempering or as---cast as required to meet the specified mechanical properties. Tensile test requirements are shown in Table 4---8. Tensile test coupons are cast in separate molds in accordance with the provisions of ASTM A48.4) 1. Cast iron gears are rated according to AGMA practice based on hardness.5) 2. Diameter. and testing should be performed in accordance with ASTM A48.50 (6. At least one hardness test should be made on each piece.8) 0.88 (22. the chemical analysis is left to the discretion of the casting supplier as necessary to produce castings to the specification.00 (12. is at the option of the producer unless specified by the gear manufacturer. Test coupon mold design shall be in accordance with ASTM A536.4---12. (4) Mechanical Properties. Tensile tests should only be required when specified. Ductile iron castings are made by the electric arc furnace. 1 ASTM Class Number 20 30 35 40 50 60 (4) Mechanical Properties. Thickness of Tooth Section.8---25. Therefore. the chemical analysis is left to the discretion of the casting supplier as necessary to produce castings to the specification. Hardness tests should be made on the mid rim thickness or mid face width of the tooth portion diameter.4) 1. These heat treatments produce ferritic.750 (19. Table 4---8 Minimum Hardness and Tensile Strength Requirements for Gray Cast Iron ANSI/AGMA 155 180 205 220 250 285 Tensile Strength ksi (MPa) 20 (140) 30 (205) 35 (240) 40 (275) 50 (345) 60 (415) 1 See ASTM A48 for additional information.0) 1. Ductile iron. sometimes referred to as nodular iron. cupola or induction practice and should be free of shrink.8.8) As Cast Machined Diameter. hardness determines the rating of the gear. Ductile iron castings shall be heat treated by annealing. Standard Specifications for Gray Iron Casting.50 (12. 4. 0 6. with length over diameter of one or more. Over 6 (152) Hardness tests should be performed in accordance with ASTM Designation E10. several ranges of engineering properties can be achieved. a sample testing plan is generally used with the approval of the gear manufacturer. all poured from the same ladle or heat. they shall be made 90 degrees apart on both cope and drag side.Gear Materials and Heat Treatment Manual When eight hardness tests are specified. refer to ASTM A536. 156---217 60 (415) 65 (450) 40 (275) 45 (310) 187---255 241---302 Range Specified 80 (550) 100 (690) 120 (830) 55 (380) 70 (485) 90 (620) Elongation in 2 inch (50 mm) percent min 18. if tensile bar fails to meet requirements. For solid cylindrical pieces. Number of Hardness Tests 1 2 4 8 4. ADI permits lowANSI/AGMA er machining and heat treat cost and replacement of more costly forgings for certain applications. in(mm) To 12 (305 ) Over 12 (305) to 36 (915) Over 36 (915) to 60 (1525) Over 60 (1525) Number of Hardness Tests 1 2 4 NOTE: The hardness tests shall be spaced uniformly around the circumference. Tensile Brinell Strength Hardness Range ksi (MPa) A---7---a Annealed Ferritic A---7---b As---Cast or Annealed Ferritic---Pearlitic A---7---c Normalized Ferritic---Pearlitic A---7---d Quench & Tempered Pearlitic A---7---e Quench & Tempered Martensitic Min. Standard Method of Test for Brinell Hardness of Metallic Materials. This treatment results in a unique microstructure of bainitic ferrite and larger amounts of carbon stabilized austenite. The higher properties of ADI are achieved by closely controlled chemistry and an austempering heat treatment. Tensile tests should be performed in accordance with ASTM Designation E8. NOTE: Other tensile properties and hardnesses should be used only by agreement between gear manufacturer and casting producer. in(mm) To 3 (76) incl. Number of hardness tests per piece is based on the diameter of the casting as follows: Outside Diameter of Casting. 17 2004---B89 . When many small pieces are involved. but is still an emerging technology.0 12. Over 3 (76) to 6 (152) incl. and two tests on the drag side 90 degrees away from the tests on the cope side. Standard Method of Tension Testing of Metallic Materials.0 2. With variation in austempering temperature and transformation time. Yield Strength ksi (MPa) 170 max.8. Table 4---9 Mechanical Properties of Ductile Iron 1 ASTM Grade Designation 60---40---18 65---45---12 80---55---06 100---70---03 120---90---02 Former AGMA Class Recommended Heat Treatment Min.3 Austempered Ductile Iron.2 percent offset method. Hardness tests should be made on the mid rim thickness or mid face width of the tooth portion diameter.0 3. Austempered Ductile Iron (ADI) is a ductile iron with higher strength and hardness than conventional ductile irons. For required retesting. The yield strength is normally determined by the 0. and heat treated in a single furnace load. ADI has been utilized in several significant applications. the number of hardness tests should be as follows: Diameter of Tooth Portion. When four hardness tests are required. one should be made on the cope side over a riser and the other on the drag side approximately 180 degrees away between risers. two tests should be made on the cope side. such as automotive ring gears and pinions.4.0 1 See ASTM A536 or SAE J434 for further information. When two hardness tests are required. one over a riser and the other approximately 180 degrees away between risers. 4.4 Malleable Iron.) rately determined using special microhardness measurement techniques. Salt baths and water quench systems should be avoided. (4) Powder metal gears can be combined with other parts such as cams. alloy steel is usually specified for gear applications.Gear Materials and Heat Treatment Manual Test programs are currently underway which will more clearly define operational properties of ADI. True involute gears are less difficult and may be less costly to pro- 18 2004---B89 . The ductility of powder metal parts is substantially lower than for wrought steels.0 percent or less and an apparent hardness of HRB 60---85. 4. Although this process is much more costly than the conventional powder metal process. Carburizing and carbonitriding can be performed. but parts will achieve a file hard surface. Penetration hardness testing cannot be correlated to material strength. Powder metal parts are formed by compressing metal powders in a die cavity and heating (sintering) the resultant compact to metallurgically bond the powder particles. Density is the most significant characteristic of powder metal materials.8 g/cm# will not develop a definite case due to the ease of diffusion through the more porous lower density material. and have extra support strength at the blind end.. Heat treated powder metal alloys have tensile strengths of 100 to 170 ksi (690---1170 MPa) with elongations of 1. and assorted components. Powder metal preforms are heated to forging temperature and finished forged to final shape and density. The powder metal process is well---suited to the production of gears for several reasons: (1) Carbide dies provide consistent part accuracy over long runs. This has generally been replaced by ductile iron. it can still be cost effective for high production parts requiring higher mechanical properties than achievable using the standard process. “As sintered” alloy steels have a tensile strength range of 40---80 ksi (275---550 MPa). (3) Powder metal gears can be made with blind corners. ratchets. high production quantities are usually necessary to realize savings. however. especially for the internal type of gears. but must be specified as “apparent hardness” since the hardness value obtained using a standard tester (either HRB or HRC) is a combination of the powder particle hardness and porosity. i. but must be processed in a controlled atmosphere to prevent changes in surface chemistry. higher strengths are achieved at higher density levels. but products with a density under 6. helical. miter.e. thus eliminating undercut relief that is needed with cut gears.8. and obtain characteristics and shapes difficult to obtain by other methods. other gears. Secondary operations such as repressing or sizing may be used to obtain precise control of shape and size or to improve mechanical properties. depending on density and alloy selected.4 g/cm# can be achieved using secondary operations. For a given composition. The controlled porosity in powder metal parts permits their impregnation with oil to provide a self lubricating part. 4. and other special gear forms are.8. possible in powder metal with sufficient development. (2) Retention of some porosity contributes to quietly running gears and allows for self---lubrication.5 Powder Metal (P/M). In recent years. The actual hardness of the powder metal material will be higher than the apparent hardness reading and can be more accuANSI/AGMA Spur gears are the easiest to produce out of powder metal because of the vertical action of the press and ease of ejection of the preform from the die cavity before sintering. Bevel. Malleable iron is a heat treated white (chilled) iron which can be produced with a range of mechanical properties depending on the alloying practice and heat treatment. However. powder metal processes have improved to the point where a typical density of 7. because of molding die costs. with an elongation of 4. provide accurate dimensional control over large production runs.0 percent or less. (Refer to ASTM A220. Further improvements in strength can be achieved by the use of hot forming powder metal. mechanical properties are proportional to density. The powder metal process is used to reduce cost by eliminating machining operations. Parts can be heat treated after sintering. Parts processed in this manner have strengths and mechanical properties approaching the properties of wrought materials. Hardness specifications can be developed for powder metal parts. Although several powder metal materials are available.0 to 7. is commonly manufactured of vacuum degassed alloy steel. meaning that the mechanical properties (tensile ductility and fatigue and impact strength) vary according to the direction of hot working or inclusion flow during forming (see Fig 4---2). martensitic and precipitation hardening stainless steels. such as for aerospace and special high speed. austenitic. Improved steel cleanliness has the effect of improving the transverse and tangential properties of forged steel in order to approach. high speed steels. molding. Castings generally being isotropic (non---directionality of properties). Wrought or forged steel is generally considered more sound than castings because the steel is hot worked. and zinc. or Fabricated Steel Gearing.Gear Materials and Heat Treatment Manual duce in sufficient quantities than by other methods because tooth configuration is not a limitation. further refined at premium cost by vacuum arc remelt (VAR) or electroslag remelt (ESR) processing. In addition to materials used for gears which are described in this Manual there are other ferrous materials used for gears. with the direction of inclusion (metal) flow parallel to the profile of teeth. Forged or hot rolled die generated gear teeth. Mechanical property data is normally measured in the longitudinal direction. the longitudinal properties. They have good wear resistance but do not possess the same degree of corrosion resistance. Most of these are used in worm gearing where the reduced coefficient of friction between dissimilar materials and increased malleability are desired. These include hot work tool steel (H series). They possess excellent rubbing characteristics and wear resistance which permits use in gears and worm wheels for severe wear applications. Gear rims are normally forged or rolled rings. however. Non---ferrous gears are made from alloys of copper. 4. formed alloy plate. with quality becoming increasingly important as tooth loads. The welded assembly should. This alloy is the basic gear alloy and is commonly designated as SAE C90700 (obsolete SAE 65) and is referred to as tin bronze.10 Copper Base Gearing. They achieve mechanical properties through alloying without heat treatment. This is the name given to a family of high strength yellow brasses. Special gear analyses are frequently used in applications with very high strength requirements. Gear rims used in the annealed condition can be stress relieved at 1250_F (675_C). Hardenability of the gear rim steel must be adequate to enable a 1000_F (540_C) minimum tempering temperature to obtain hardness.6 Other Ferrous Materials. when sound in the rim tooth section. and non---destructive inspection (magnetic particle and ultrasonic or radiograph) practices. aluminum. etc. (2) Manganese Bronzes. Application is limited because quantities or critical application considerations must justify the increased development and die costs. They are characterized by high strength and hardness and are the toughest materials in the bronze family.) improve cleanliness and produce higher quality steel. A family of four bronzes accounts for most of the nonferrous gear materials. etc. Critical application gearing. cast. result in the optimum direction of inclusions for gearing. ladle refined. down time costs and safety considerations increase. wearability NOTES: Mechanical properties in the transverse direction will vary with inclusion type and material form.9 Selection Criteria for Wrought.8. be stress relieved at 950_F(510_C) minimum [50_F(28_C) below the tempering temperature]. barstock. Fabricated (welded) gears are generally manufactured when they are more economical than forged or cast gears. Cast. can provide comparable mechanical properties to those of forgings. mainly because of their “wear resistance” characteristics for withstanding a high sliding velocity with a steel worm gear.1 Gear Bronzes. casting. therefore. less frequently. These and other more economical refining processes (AOD. Inclusions in wrought steel forgings. Alloys of copper are in wide use for power transmission gearing. (1) Phosphor or Tin Bronzes. Selection of the gear blank producing method for most applications is primarily a matter of economics. heat treating ANSI/AGMA 19 2004---B89 . 4. or. These bronzes have the same strength and ductility as annealed cast steel. rolled rings and plate are perpendicular to the root radius or profile of machined gear teeth. 4.10. These bronzes are tough and have good corrosion resistance. but not equal. Wrought steel is anisotropic. Casting quality involves controlled steel making. 4. Fig 4---2 Directionality of Forging Properties er strength. but they are more difficult to machine. This bronze has good wear resistance and has low coefficient of friction against steel. Other brass materials are used because of their highANSI/AGMA 20 2004---B89 . ductility is reduced.Gear Materials and Heat Treatment Manual or bearing quality as phosphor and aluminum bronzes. Gear brasses are selected for their corrosion resistant properties.10. As the strength of aluminum bronze is increased. (4) Silicon Bronzes. Bearing characteristics are better than for manganese bronze but are inferior to the phosphor bronzes. Aluminum bronze materials are similar to the manganese bronzes in toughness.2 Gear Brasses and Other Copper Alloys. but are lighter in weight and attain higher mechanical properties through heat treatment. used because of its good machinability. (3) Aluminum Bronze. DIRECTION OF METAL AND INCLUSION FLOW ROLLED RING FORGING LONGITUDINAL TENSILE TEST BAR OR PROPERTIES TRANSVERSE TENSILE TEST BAR DIRECTION OF METAL AND INCLUSION FLOW PINION FORGING TRANSVERSE TENSILE TEST BAR LONGITUDINAL TENSILE TEST BAR TANGENTIAL TENSILE TEST BAR NOTE: ASTM E399 may be used if impact testing is required. Wear resistance of these brasses is somewhat lower than for the higher strength manganese bronzes. Silicon bronzes are commonly used in lightly loaded gearing for electrical applications because of their low cost and nonmagnetic properties. 4. The most common gear brass is yellow brass. Hardness tests are normally made in accordance with ASTM E10.4. as agreed to by the gear manufacturer and casting producer. Copper Base castings are heat treated as required to obtain the specified mechanical properties. (5) Casting Tensile Properties. Castings should also be furnished free of sand and extraneous appendages. The load in kilograms force listed in Table 4---13 should be used. The chemical analysis shall be determined from a sample obtained during pouring of the heat. 4. if required. hardness and hardness control. and other copper alloys. cast structure and supplementary data for cast copper alloys is as follows: (1) Casting Manufacture.10. The properties in the casting are dependent upon the size and design of the casting and foundry practice. (4) Casting Hardness. 4. ASTM Designation E54. The number of hardness tests made should be specified by the gear manufacturer. may be used as the referee method. heat treatment.Gear Materials and Heat Treatment Manual 4. 4.10. The gear manufacturer may perform a product analysis for chemistry. heat treating.10. Copper base castings are specified by melting method. Tensile test bars for centrifugal castings may be cast in a separate centrifugal mold for test bars or cast in a chill test bar mold. Table 4---10 presents chemical analyses of common wrought bronze alloys. Specifications describe type of bronzes according to chemical analysis. Tensile test bars for sand castings may be attached to casting or cast separately. Method of Test for Brinell Hardness of Metallic Materials. Repair welding in other than the tooth portion may be performed by the casting supplier. Chemical analysis shall be in conformance with the type specified or ANSI/AGMA 21 2004---B89 . leaded tin bronze (improved machinability) and higher strength manganese bronze and aluminum bronze. brasses. hardness and tensile properties. tensile properties. This group of gear materials includes bronzes. Refer to Table 4---12 for chemical analyses of common cast copper bronze alloys. Tensile test bars for static chill castings may be cast separately with a chill in the bottom of the test bar mold. Cast copper base gear materials may be melted by any commercially recognized melting method for the composition involved. (3) Casting Chemical Analysis. analysis or type. gas holes and entrapped sand in the tooth portion. NOTE: An integral or separately cast test bar does not necessarily represent the properties obtained in the casting. chemical analysis. Standard Methods of Chemical Analysis of Special Brasses and Bronzes. Tensile tests are only required when specified. Additional information regarding manufacturing.10. Heat treated castings should have the test coupons heat treated in the same furnace loads as the casting they represent. Tensile tests when specified are made in accordance with ASTM E8.3 Wrought Copper Base.4 Cast Copper Base.2 General Information for Copper Castings. Castings should be free of shrink. Wrought copper base materials is a general term used to describe a group of mechanically shaped gear materials in which copper is the major chemical component. porosity. Three test coupons shall be poured from each melt of metal or per 1000 lbs (454 kg) of melt except where the individual casting weighs more than 1000 lbs (454 kg). (2) Casting Heat Treating. Mechanical properties of separate cast test specimens are shown in Table 4---13.1 Cast Worm Bronzes.4. including phosphor or tin bronze. Repair welds in the tooth area should be performed only with the approval of the gear manufacturer. Hardness tests are to be made on the tooth portion of the part after final heat treatment. while Table 4---11 presents typical mechanical properties of these wrought bronze alloys in rod and bar form. Tension Testing of Metallic Materials. In the event of disagreement in chemical analysis. 50 to 1. 0. see SAE Information Report SAE J461. For cross reference to SAE.2 0. Table 4---11 Typical Mechanical Properties! of Wrought Bronze Alloy Rod and Bar Bronze2 Alloy UNS NO.0 --.0 0.--- 0.--- 1.25 C67300 --.5 to 2.50 0.--- 95 (655) 50 (345) 12 200HB (3000kgf) ALBR 6 90 (620) 45 (310) 17 100 HRB ALBR 5 93 (640) 60 (415) 26 90 HRB 70 (485) 40 (275) 25 70 HRB --.0 0.0 to 11.5 0. 0.6 0.50 0.--- 1 Typical mechanical properties vary with form.30 Rem. For added copper alloy information. and section size considerations.20 --.30 9.Gear Materials and Heat Treatment Manual Table 4---10 Chemical Analyses of Wrought Bronze Alloys Bronze 1 Alloy UNS NO. Hardness HB and HRB --. also see SAE J463.20 0. former SAE & ASTM.0 to 11. ANSI/AGMA 22 2004---B89 .30 0.--- 1.5 to 11.--- 2.0 --.40 to 3. For added wrought copper alloy information.--- 0.25 C63000 ALBR 6 Rem.5 --.10 1.0 to 3.25 C62400 --.0 to 4.--- Rem.25 4.60 --. Percent Maximum (unless shown as a range or minimum) Cu (incl Ag) Pb Fe Sn Zn Al As Mn Si Ni (incl Co) C62300 --.--- 10.0 0.5 C64200 ALBR 5 Rem.20 0. --.25 2.0 0.5 0.--- Rem. 2 Unified Numbering System.0 to 4. --.05 0.30 0.0 to 4. also see SAE J463.0 --. see SAE Information Report SAE J461. --.--- 2.50 6.--- 58.3 to 7.--- 90 (620) 45 (310) 25 180HB (1000kgf) --.--- 2.15 --.50 0. former SAE & ASTM. For cross reference to SAE. min.5 0.0 to 63.0 to 5.25 0. Former AGMA Type Composition. temper.--- 8.--- 1 Unified Numbering System. C62300 C62400 C63000 C64200 C67300 Former AGMA Type Tensile Strength ksi (MPa) Yield Strength ksi (MPa) Elongation in 2 in (50 mm) percent. 25 1.--- --.0 to 66.--- C95200 ALBR 1 86.0 min --.--- --.0 to 4.--- --.--- --.50 0.0 to 7.8 to 1.30{ 0.8 to 4.--- --.--- 3.0 to 66.005 --.--- 0.50 0.--- 10.20 0.5 0.--- --.25{ 0.0 0.05 0.8 to 1.0 to 4.0 to 11.5 --.0 to 11.0 --.005 --.4 to 2.--- --.0 0.--- 82.0 to 11.--- 2.5 to 4.25 0.5 --.05 0.--- 5.0 9.--- --.0 2.--- C92700 MNBR 3 86.0 10.5 to 5.--.--- C95400 ALBR 3 83.--- 0.5 --.--- C95300 ALBR 2 86.005 --.0 to 4.50 0.--- --.20 0.0 to 3.0 1.0 min --.--- --.5 --.--- --.--- --.005 0.--- C92900 --. ANSI/AGMA 23 2004---B89 .15 0.5 to 9.0 2.0 --.5 * Unified Numbering System.0 to 60.0 --.9 --.5 C90700 MNBR 2 88.0 0.0 0.05 0.05 0. phosphorus shall be 1.005 --.005 0.0 --.0 to 11. see SAE Information Report SAE J461.--- --.10 to 1.0 --.50{ 8.--- 2.--- 3.Gear Materials and Heat Treatment Manual Table 4---12 Chemical Analyses of Cast Bronze Alloys Bronze Former Alloy * AGMA UNS NO.--- 2.5 percent maximum.0 to 5.005 0.20 0. also see SAE J462.--- --. Percent Maximum (unless shown as a range or minimum) Cu Sn Pb Zn Fe Ni Sb (incl Co) S P Al Si Mn C86200 MNBR 3 60.25 0.0 C86300 MNBR 4 60.0 --.0 to 90.0 to 2.5 --.5 --.0 --.--- --. { For continuous castings.--- --.0 min --.30{ 0.0 10.--- 1.0 9.--- C92500 MNBR 5 85.0 to 42.30 0.--- 0. Type Composition.5 --.--- 1.0 --.--- 0.0 0.25{ 0.--- --.0 1.5 to 5.--.--- 10.--- --.0 to 89.005 0.5 0.0 to 5.0 2.--- 9.20 0.25 2.20 22. For added copper alloy information.5 --.0 to 12.0 to 1.2 0.--- 2.--- 3.--- 1.0 0. For cross reference to SAE.0 to 28.5 to 1.--- 3.--- --.--- 3.70 0.5 0.0 1.5 C95500 ALBR 4 78.0 C86500 MNBR 2 55.0 to 5. former SAE & ASTM.20 22.20 0.0 to 28.0 min --.0 to 11.0 to 12.0 0.0 --.--- 0.0 to 88.0 --.0 to 86.5 0.40 36. Centrifugal Continuous 90 (620) 45 (310) 18 --. k s . Centrifugal Continuous 65 70 (450) (485) 25 (170) 25 (170) 20 25 112 112 --.Gear Materials and Heat Treatment Manual Table 4---13 Mechanical Properties of Cast Bronze Alloys! Copper Alloy UNS. Centrifugal Continuous Sand. Centrifugal Continuous Sand.----.2 NO. Table 3 footnote).--- C92500 BRONZE 5 C92500 BRONZE 5 Sand Continuous 35 40 (240) (275) 18 (125) 24 (165) 10 10 70 80 --.--- 225 225 C86500 MNBR 2 C86500 MNBR 2 Sand. Continuous 45 (310) 25 (170) 8 90 --. Centrifugal Continuous 65 68 (450) (470) 25 (170) 26 (180) 20 20 --.----. Centrifugal Continuous Sand. also see SAE J462. former SAE & ASTM. Centrifugal Continuous (HT) 65 70 80 80 (450) (485) (550) (550) 25 26 40 40 (170) (180) (275) (275) 20 25 12 12 --------- --------- 140 140 160 160 C95400 C95400 C95400 C95400 ALBR 3 ALBR 3 ALBR 3 ALBR 3 Sand. Centrifugal (HT) Continuous (HT) 75 85 90 95 (515) (585) (620) (655) 30 32 45 45 (205) (220) (310) (310) 12 12 6 10 --------- --------- 160 160 190 190 C95500 C95500 C95500 C95500 ALBR 4 ALBR 4 ALBR 4 ALBR 4 Sand.--- C95200 ALBR 1 C95200 ALBR 1 Sand. ANSI/AGMA 24 2004---B89 . 2 Unified Numbering System.--- 180 110 110 (760) (760) 60 (415) 62 (425) 12 14 --. 5 BHN at other load levels (1000 kgf or 1500 kgf) may be used if approved by purchaser.--- 1 For rating of worm gears in accordance with AGMA 6034---A87. For added copper alloy information. 4 Minimum tensile strength and yield strength shall be reduced 10% for continuous cast bars having a cross section of 4 inch (102 mm) or more (see ASTM B505. see SAE Information Report SAE J461. will depend upon the particular casting method employed.--- C92700 BRONZE 3 C92700 BRONZE 3 Sand Continuous 35 38 (240) (260) 18 (125) 20 (140) 10 8 70 80 --. Former AGMA Type C86200 MNBR 3 Casting Method & Condition # Minimum Typical Hardness % Percent Minimum Minimum 4 4 HB HB Tensile Strength Yield Strength Elongation in 2 inch ksi (MPa) 500 3000 ksi (MPa) (50 mm) kgf kgf Sand. the Materials Factor. For cross reference to SAE.----.----.----. Centrifugal (HT) Continuous (HT) 90 95 110 110 (620) (655) (760) (760) 40 45 60 62 (275) (290) (415) (425) 6 10 5 8 --------- --------- 190 190 200 200 C86300 MNBR 4 --.----.----.--- C92900 Sand. 3 Refer to ASTM B427 for sand and centrifugal cast C90700 alloy and sand cast C92900.--- 125 125 C95300 C95300 C95300 C95300 ALBR 2 ALBR 2 ALBR 2 ALBR 2 Sand. Centrifugal (HT) Continuous Sand.--- C90700 BRONZE 2 C90700 BRONZE 2 C90700 BRONZE 2 Sand Continuous Centrifugal 35 40 50 (240) (275) (345) 18 (125) 25 (170) 28 (195) 10 10 12 70 80 100 --. The following supplementary requirement should apply only when specified by contractual agreement. The average properties of these two bars must meet specified requirements for acceptance of the lot.Metallic Materials. 4. chemistry. and foundry technique. The gear manufacturer can select at random any number of castings from a given lot to determine the hardness at or within 1 inch (25mm) of the cast OD or as indicated on gear manufacturer’s drawing. size. Ferrous gearing may be through hardened or surface hardened when gear rating or service requirements warrant higher hardness and strength for improved fatigue strength or wear resistance. (a) With proper foundry technique. In addition to the more common non---ferrous materials used for gears. Because of the wide range of non---metallic materials. 5. and quietness of operation. Heat Treatment Heat treatment is a heating and cooling process used to achieve desired properties in gear materials. castings and. using a 500 kg load. the producer should furnish specified microspecimens or photomicrographs for each melt with the certificate of hardness.11 Other Non--.Gear Materials and Heat Treatment Manual One test specimen should be tested from each group of three test coupons cast. The minimum hardness at or near the root diameter shall be agreed upon by the purchaser and the casting producer. shall be 80 HB for static chill and centrifugal chill castings. and the successful use of plastic gears in many applications have all contributed to the establishment of certain plastics as engineering material suitable for fine pitch gears. The lot should consist of all gears produced from one melt of metal. Plastics are being used at a rapidly increasing rate as gear materials in the fine pitch range. (1) Preheat treatments--Anneal Normalize and temper Quench and temper Stress relief (c) The grain size of cast copper base alloys varies as a function of cooling rate and section thickness. Failure of any gear to meet hardness requirements specified is subject to rejection. in particular. When required. resistance to water absorbtion. the two remaining specimens shall be tested.12 Non--. (d) The grain size of static cast copper base alloys should be mutually agreed upon by the consumer and producer with reference to the various sections of the ANSI/AGMA Surface harden profile heated (flame and induction harden) and profile chemistry 25 2004---B89 . advances in gear mold design and molding technology. (7) Cast Structure. It does not express the specific properties and characteristics of the casting which are greatly dependent on design. Recommended maximum grain size for centrifugal castings is 0. the lot should be accepted.070 mm in the web and 0. normalize. Non---metallic gears are usually selected for properties such as low friction. the tooth section. and quench and temper). If the first bar fails to meet the specified requirements. engineering data on the various types of non---metals is usually most easily available from the producers. or normalize and temper. If this bar meets the tensile requirements.Ferrous Materials. Specifications are specialized and should be resolved between the user and supplier. Determination of hardness at or near the root diameter is optional and should be agreed upon by the purchaser and gear manufacturer. are produced from non---metallic materials. (2) Heat treatments--Through harden (anneal.) (8) Supplemental Data. The grain size for copper base alloys is determined per ASTM E112 at 75X magnification.120 mm in the hub. ability to operate with no lubricant.035 mm in the rim. Improved materials. development of engineering data. and mechanical properties. Details of this supplementary requirement should be agreed upon by the casting producer and gear manufacturer. Common heat treatments for ferrous materials include: (b) An integral or a separate test bar simply signifies the melt quality poured into the mold to make the casting. particularly those used to transmit motion rather than power. and 70 HB for sand castings. the properties of static chilled and centrifugal cast separate test bars should be the same. several wrought aluminum and beryllium copper alloys are occasionally used. Many gears. (6) Casting Hardness Control. (See Appendix A and AGMA 141. The minimum hardness. 4. It may be advisable to specify by use of photomicrographic standards both acceptable and non---acceptable phase distributions in the gear rim section. 0. dimensional stability and improved machinability. Parts are normally air cooled from tempering temperatures. There are generally three methods of heat treating through hardened gearing.Gear Materials and Heat Treatment Manual modified (carburize. Annealing may be the final treatment (when low hardness requirements permit) or is typically a pretreatment applied to the cast or wrought gear blank in the “rough. Through hardened gears are heated to a required temperature and cooled in the furnace or quenched in air. ANSI/AGMA (2) When the hardness and mechanical properties required for a given gear application can be achieved more economically by quench and temper 26 2004---B89 . 5. Austempering is used. Selection of the tempering temperature must be based upon the specified hardness range. material composition. to achieve the desired mechanical properties. not discussed. Modifications of quench hardening. See 4.1. 5. therefore. Specialized heat treatment for nonferrous materials should be recommended by the producer. Annealing consists of heating steel or other ferrous alloys to 1475---1650_F (802---899_C).1 Through Hardening Processes. 5. The hardness and mechanical properties achieved from the quench and temper process are higher than those achieved from the normalize or anneal process. and furnace cooling to a prescribed temperature [generally below 600_F (316_C)]. regardless of section size.1. The normalizing and annealing processes are frequently used. with hardness being a function of grade of steel and the part section thickness. (3) Post heat treatment--Stress relieve 5.1 Applications.6 for discussion of hardenability.1.2 Normalizing. carbonitride. generally below 1275_F(691_C). Typical hardness for annealed gearing is shown in Table 4---2. NOTE: Through hardening does not imply equal hardness through all sections of the part.1. Alloy steels are normally tempered at 1000---1250_F (538---677_C) after normalizing for uniform hardness. for through hardened (approximately 300 to 480 HB) ductile cast iron gears. The tempered hardness varies inversely with tempering temperature. Normalizing results in higher hardness than annealing. Table 4---3 gives hardness guidelines for some steel grades. These processes are used in wrought steel to reduce metallurgical non---uniformity such as segregated alloy microstructures (banding) and distorted crystaline microstructures from mechanical working. normalizing does not increase hardness significantly more than annealing.4. with plain carbon steels containing up to about 0. followed by rapid quenching. The rapid cooling causes the gear to become harder and stronger by formation of martensite. Tempering reduces the material hardness and mechanical strength but improves the material ductility and toughness (impact resistance). Normalizing consists of heating steel or other ferrous alloys to 1600---1800_F (871---982 _C) and cooling in still or circulated air. 5.4 percent carbon. however. followed by a 1200_F (649_C) temper with controlled cooling to 600_F (316_C). Cycle annealing is a term applied to a special normalize/temper process in which the parts are rapidly cooled to 800---1000_F (427---538_C) after normalizing at 1600---1750_F (871---954_C). The quench and temper process on ferrous alloys involves heating to form austenite at 1475---1600_F (802---871_C). The quench and temper process should be specified for the following conditions: (1) When the gear application stress analysis indicates that the hardness and mechanical properties for the specified material grade can best be achieved by the quench and temper process. occur infrequently for steel gearing and are.1 Annealing. gas or liquid. Through hardening may be used before or after the gear teeth are formed.1. 5.” It results in low hardness and provides improved machinability and dimensional stability (minimum residual stress). The gear is then tempered to a specific temperature. However. annealing. and nitride) Typical specified hardness ranges for normalized and tempered steels are shown in Table 4---2. and the as quenched hardness. and quenching and tempering. as a homogenizing heat treatment for alloy steels.4 Quench and Temper. such as austempering and martempering.3 Normalizing and Annealing for Metallurgical Uniformity. either singularly or in combination. normalizing (or normalizing and tempering). In ascending order of hardness for a particular type of steel they are. 1.4 Designer Specification. and the material. induction hardening. 8th or 9th edition. while the alloy composition determines the hardness gradient which can be achieved through the part.” 5.4. the quenched hardness of the part. 5.1. Appendix B illustrates the controlling section for various gear configurations whose teeth are machined after heat treatment.4. than by normalizing or annealing.1. 5.Gear Materials and Heat Treatment Manual of a lower alloy steel. which improves ductility and toughness or impact resistance. Tables in the appropriate reference are available as guidelines for the effect of tempering temperature on hardness. 5. 27 2004---B89 . Temper brittleness should not be confused ANSI/AGMA 5.25---0. Heat Treating. this has been interpreted to mean that the specified hardness must be met at this location. (3) When it is necessary to develop mechanical properties (core properties) in sections of the part which will not be altered by subsequent heat treatments (for example nitriding.3 Tempering. The optimum tempering temperature is the highest temperature possible while maintaining the specified hardness range.4. care should be taken to avoid needlessly increasing material costs by changing to a higher hardenability steel where service life has been successful. with the tempering embrittlement phenomenon from tempering in a lower range (500---600_F) often referred to as “500_F or A---Embrittlement. The hardness range should be a 4 HRC or 40 HB point range. For more information. However. (3) Any testing required. If gear root hardness is critical to a specific design criteria. The designer should specify the following on the drawing.50 percent has been shown to eliminate temper brittleness in most steels. This phenomenon is called “temper brittleness” and is generally considered to be caused by segregation of alloying elements or precipitation of compounds at ferrite and prior austenite grain boundaries. Hardness after tempering varies inversely with the tempering temperature used. electron beam hardening. CAUTION: Some steels can become brittle and unsuitable for service if tempered in the temperature range of 800---1200_F (425---650_C). The designer should not specify a tempering temperature range on the drawing.1.1.7 Additional Information.6 for more information on hardenability. Volume 4. For example. Designers often interpret this to mean that minimum hardness is to be obtained at the roots of teeth for gear rating purposes. investigate the specific material’s susceptibility to temper brittleness and proceed accordingly. If the part under consideration must be tempered in this range. Refer to 4.4. The tempering temperature must be carefully selected based upon the specified hardness range. hardness tests. and laser hardening). The specified hardness of through hardened gearing is generally measured on the gear tooth end face and rim section.6 Maximum Controlling Section Size.4. Tempering lowers hardness and strength. Tempering below 900_F(482_C) should be approved by the purchaser. 5. Historically. (1) Grade of steel (2) Quench and temper to a hardness range. Since depth of hardening depends upon grade of steel (hardenability). controlling section size (refer to Appendix B) and heat treat practice.4. Specifying both tempering temperatures and hardness ranges on a drawing causes an impractical situation for the heat treater. The maximum controlling section size is based upon the hardenability of alloy steel for through hardened gear blanks. It is best to specify a hardness range and allow the heat treater to select the tempering temperature to obtain the specified hardness. consult the following: The ASM Handbook. Parts are normally air cooled from the tempering temperature. the gear tooth root hardness should be specified. Molybdenum content of 0. flame hardening. including the frequency of testing. achieving specified hardness on these surfaces may not necessarily insure hardness at the roots of teeth. or any non---destructive tests such as magnetic particle inspection or dye penetrant inspection.1. The major factors of the quench and temper process that influence hardness and material strength are: (1) (2) (3) (4) Material chemistry and hardenability Quench severity Section size Time at temperature The steel carbon content determines the maximum surface hardness which can be achieved.2 Processing Considerations.5 Specified Hardness. 1. Stress relief below 900_F(482_C) is not recommended. Gearing can also be tooth to tooth. However. because both the flanks of teeth and root diameter are hardened. or other fabricating techniques. 5. to heat the root diameter and opposite flanks of adjacent teeth. Cold Drawn. Stress Relieved Steel Bars. Stress relief is a thermal cycle used to relieve residual stresses created by prior heat treatments. progressively hardened by passing the flame or inductor and following quench head between the roots of teeth. Size limitations and mechanical properties are listed in Table 4---5. These processes develop a hard wear resistant case on the gear teeth. Flame or induction hardening of gearing involves heating of gear teeth to 1450---1600_F(788---871_C) followed by quench and tempering. fatigue properties of this steel may not be equivalent to quench and tempered steel with the same tensile properties.Gear Materials and Heat Treatment Manual Military specification MIL---H---6875 and Mil--STD---1684. only the surface is hardened during quenching (see Figs 5---1 and 5---2). stress relieved bars may be used as an alternative to quench and tempered steel. the gear element within the heat source (flame or induction coil) which envelopes the entire face width. is time consuming and is not economical for small. The heat source and quench head traverse axially along the length to be hardened. Inductor or flame heads or burner may be designed either to pass in the root diameter between flanks of adjacent teeth. When only the surface is heated to the required depth. Shafting and gearing can also be progressively spin hardened by spinning the shaft or tooth section within the heat source and following quench head. Residual tensile stress in the roots of teeth may also prove detrimental. while the gear element is submerged in a synthetic quench (termed “Delapena Process”). An encircling coil or tooth by tooth inductor is used for induction hardening.1. The ideal temperature range for full stress relieving is 1100---1275_F (593---691_C). An inductor or flame head which encompasses only top lands of teeth and adjacent flanks followed by quenching provide wear resistance to the flanks. Material selection and heat treat condition prior to flame or induction hardening significantly affects the hardness and uniformity of properties which can be obtained. Gearing is removed from the heat source and immediately hardened by the quenchant. It is. Lower temperatures are sometimes used when 1100_F (593_C) temperatures would reduce hardness below the specified minimum.5 Stress Relief. machining. 5. like other tooth to tooth hardening techniques. This process. An oxyfuel burner is used for flame hardening.2 Flame and Induction Hardening. finer pitch gearing (finer than 10 DP). For further details see ASTM A---311. Spin hardening is more economical for smaller gears. but endurance or bending strength in the roots is not enhanced.1 Methods of Flame and Induction Hardening. 5. cold drawn.6 Heavy Draft. Both of these methods of surface hardening can be done by spin hardening. therefore. Heavy draft. 5. Spin hardening of gearing involves heating all of the teeth across the face simultaneously by spinning ANSI/AGMA 28 2004---B89 . welding. Gearing may also be tooth to tooth. Only the non---critical top lands of teeth are not hardened. or may fit or encompass the top land to heat the top land and opposite flanks of each tooth. or by tooth to tooth hardening. cold working.2. recommended that both the designer and heat treater know what type of hardening pattern is desired. Lower temperatures with longer holding times are sometimes used. progressively hardened by passing the inductor between the roots of adjacent teeth. Heat sources designed to pass between adjacent teeth followed by quenching are desirable from both endurance or bending strength and wear considerations. NOTE: Stress relief below 1100_F(593_C) reduces the effectiveness. Fig 5---1 Variation in Hardening Patterns Obtainable on Gear Teeth by Flame Hardening ANSI/AGMA 29 2004---B89 . AND ARE DEPENDENT UPON THE CAPACITY OF THE EQUIPMENT.Gear Materials and Heat Treatment Manual SPIN FLANK FLAME HARDENING FLAME HEAD FLAME HEAD FROM THIS TO THIS FLANK FLAME HARDENING FLAME HEAD FLAME HEAD FROM THIS TO THIS FLANK AND ROOT FLAME HARDENING FLAME HEAD FLAME HEAD FROM THIS TO THIS FLAME HEAD FLAME HEAD FROM THIS TO THIS THE HARDENING PATTERNS SHOWN ARE NOT POSSIBLE FOR ALL SIZES AND DIAMETRAL PITCHES OF GEARING. Gear Materials and Heat Treatment Manual SPIN HARDENING INDUCTION COIL OR FLAME HEAD INDUCTION COIL OR FLAME HEAD FLANK HARDENING INDUCTOR OR FLAME HEAD INDUCTOR OR FLAME HEAD FLANK AND ROOT HARDENING INDUCTOR OR FLAME HEAD Fig 5---2 Variations in Hardening Patterns Obtainable on Gear Teeth by Induction Hardening ANSI/AGMA 30 2004---B89 . NOTE: AGMA quality level will be reduced approximately one level (from the green condition) after flame or induction hardening unless subsequent finishing is performed. Parts are rotated when encircling coils are used.2. however. acetylene and propane. including (cast and wrought) carbon and alloy steels. A quench and tempered material condition or preheat treatment. followed by quenching.g.Gear Materials and Heat Treatment Manual Three basic gases are used for flame heating. shape of the inductor. etc. These processes are also 5.35---0. The higher the alloy content with high carbon. except when spin flame hardening is applied. ductile. 4140 steel with teeth coarser than 3 DP. A wide variety of materials can be flame or induction hardened.2 Application. but hardens teeth through the entire cross section. Coarser pitch teeth generally require inductors powered by medium frequency motor generator sets or solid state units. bevel. it is recommended that coarser pitched gears of leaner alloy steels receive a quench and temper pretreatment. malleable and gray cast irons. herringbone.2. Initially low audio frequency is used to preheat the root area. require longer heating cycles and a more severe quench which increase the chance of Induction heating depth and pattern are controlled by frequency. depending upon hardenability of the steel and hardening requirements. If high root hardness is not required. These processes may also be used when the maximum contact and bending strength achieved by carburizing is not required. Generally. used in place of more costly nitriding which cannot economically generate some of the deeper cases required.3 Material. ANSI/AGMA 31 2004---B89 . provides the best hardening response and most repeatable distortion. steels with carbon content of approximately 0. power density.4 Prior Heat Treatment.. helical.5 percent carbon or higher are susceptible to cracking. reducing core ductility of teeth and increasing distortion (see Fig 5---2). followed by high radio frequency to develop the profile heated pattern. high operator skill is required.P. cold drawn material because of densification from cold working. in addition to air. gearing can be obtained by dual frequency spin coil induction heating using both low (audio) frequency (AF) of 1---15 kHz and higher (radio) frequency (RF) of approximately 350---500 kHz. water or polymer solutions can be used. Cast irons also have a high tendency for cracking. Oil. which include MAPP. Contour induction is preferred over flame when root hardness and closer control of case depth is required. however. for example. Alloy steels of 0. the greater the tendency for cracking. The spin flame process generally hardens below the roots. Contour or profile hardened tooth patterns for 4---12 D. workpiece geometry and workpiece area being heated. Induction hardening employs a wide variety of inductors ranging from coiled copper tubing to forms machined from solid copper combined with laminated materials to achieve the required induced electrical currents. These structures do. Wide faced gearing is heated by scanning type equipment while more limited areas can be heated by stationary inductors. or separate by using an immersion quench tank. 5.2. For more consistent results. normalized or annealed structures can be hardened. Quenching after flame or induction heating can be integral with the heat source by use of a separate following spray. spur. Selection of the material condition of the gearing can affect the magnitude and repeatability of flame and induction hardening. In both carbon and alloy steels. Hot rolled material exhibits more dimensional change and variation than hot rolled. Simple torch type flame heads are also used to manually harden teeth. Contour flame hardening of the flanks and roots is not generally available. These gases are each mixed with air in particular ratios and are burned under pressure to generate the flame which the burner directs on the work piece. but size or configuration does not lend itself to carburizing and quenching the entire part. 5. Flame and induction hardening have been used successfully on most gear types. The general application of flame hardening is to the flanks only. martensitic stainless steels. e. flame hardening is more available and more economical than induction hardening for herringbone and spiral bevel gearing. These processes are used when gear teeth require high surface hardness. Since there is no automatic control of this process.55 percent are suitable for flame or induction hardening. Finer pitch gearing generally utilizes encircling coils with power provided by high frequency vacuum tube units. soluble oil. The allowable durability and root strength rating for the different hardening patterns should be obtained from appropriate AGMA rating practices. Root flame hardening by the tooth by tooth process is difficult and should be specified with care. 5. Successful induction hardening of either gray or ductile cast iron is dependent on the amount of carbon in the matrix. Equipment must be such that heating rates across the burner face are consistent from cycle to cycle. this is usually not a problem with properly maintained equipment since electrical power characteristics. There are two basic methods of flame or induction hardening gears. The annealed structure is the least receptive to flame or induction hardening. 5. Flame hardening may also cause burning or melting of tooth surfaces. Pearlite microstructures are desirable. Pearlite promoting alloy additions such as copper. Heat must be removed quickly and uniformly to obtain desired hardness. Accurate heating to the proper surface temperature is a critical step.2. Equipment varies from hand held torches to tailor made machine tools with well controlled movement of burner heads. Flank hardened teeth usually have an integral quench following the inductor.2. Flank or root and flank induction scan hardening (contour) can be applied to almost any tooth size with appropriate supporting equipment and kW capacity. polymer. Several areas must be considered when processing.Gear Materials and Heat Treatment Manual cracking. However. Burner or inductor design. The combined carbon in pearlite will readily dissolve at the austenitizing temperature.2 Heating with Flame or Induction. The quenchant should produce acceptable as quenched hardness. ANSI/AGMA 32 2004---B89 .2. Repeatabiltiy becomes more difficult with flame hardening. for pitches of approximately 16 DP and finer. Quench time and temperature are critical and in---spray quenching. 5. With induction. 5. these methods are not recommended. or the gear is submerged in liquid during heating. The hardening patterns shown are not possible for all sizes and diametral pitches. Spin hardening in an induction coil is recommended. a spray quench usually follows behind the coil. yet minimize cracking. Gas pressure and mixing of heating gases must be uniform. pressure velocity and direction of the quench media must be considered. 5. a coolant is used on a portion of the metal away from the heating zone to maintain the base metal near ambient temperature so the part mass can absorb heat from the heated zone. inductor movement and integral quench intensity can be readily controlled. nickel or molybdenum may be necessary to form this microstructure. For induction hardening. When localized or air quenching is used.6. spin hardening and tooth to tooth hardening.2. Overheating can result in cracking. The maximum diameter and face width of gears capable of being single shot induction coil hardened is determined by the area of the outside diameter and the kW capacity of the equipment.6. Parts heated in an induction coil are usually quenched in an integral quench ring or in an agitated quench media.5 Hardening Patterns. requirements should be worked out with the supplier.6 Process Considerations. heat input and cycle time must be closely controlled. See Figs 5---1 and 5---2 for variations of these processes and the resultant hardening patterns.1 Repeatability.6. Repeatable process control is essential for acceptable results. Burner head location must be precise from cycle to cycle. Some of the more critical requirements are outlined below. The induction coil method is generally limited to gears of approximately 5 DP and finer.3 Quenching. Spin hardening of finer pitches is also required when using flame burners. These bending strength ratings are lower at the roots of teeth when only the tooth flanks are hardened. When the part is scanned while rotating in a coil.2. For coarser pitches. tin. Long slender parts can be induction hardened with lower kW capacity equipment by having the coils scan the length of the part while the part is rotating in the coil. oil and air. Quenchants used are: water. the kW or power capacity of the equipment limits the pattern which can be attained. Underheating results in less than specified hardness and case depth. PERCENT 0.6. Tempering is mandatory only when specified. 5. depth of hardening.70 Fig 5---3 Recommended Maximum Surface Hardness and Effective Case Depth Hardness Versus Percent Carbon for Flame and Induction Hardening ANSI/AGMA 33 2004---B89 .2.5 Surface Hardness. Effective case depth for flame and induction hardened gears is normally defined as the distance below the surface at the 0. mass and quenching considerations. heating time. Profile hardening of fine pitched gearing using a submerged quench decreases the difference between pitchline and root case depth.60 CARBON CONTENT --.50 0.30 0. and separate tempering is unnecessary.5 tooth height where hardness drops 10 HRC points below the surface hardness (see Fig 5---3). effective case 60 MAXIMUM SURFACE HARDNESS 50 ∆ H= 10 EFFECTIVE CASE DEPTH HARDNESS 40 30 0. the heat affected zone (HAZ) is a region that is heated to 1300---1400_F. Tempering should be for a sufficient time to insure that hardened teeth reach the specified tempering temperature. This zone should be located either a minimum of 1/8 inch up the flank from the critical root fillet or well below the root diameter. Contour induction hardening results in case depth at the root to be approximately 60 percent of the depth at the pitchline due to mass quench and hardenabiltiy effect. Surface hardness is the hardness measured on the immediate surface and is primarily a function of the carbon content (see Fig 5---3). depth of case at the root may be specified.Gear Materials and Heat Treatment Manual 5.2.2.20 0. (704_C---760_C) but does not get hardened and thus has lower strength. When root is also to be hardened.6 Effective Case Depth.6. depth does not apply.1 Heat Affected Zone. Hardness may be lower as a result of prior heat treatment. When a tooth is through hardened.40 0. It is good practice to temper after quenching to increase toughness and reduce residual stress and crack susceptibility. judgment should be exercised before omitting tempering.2. AGMA gear rating standards should be consulted for appropriate stress numbers.7.6. Flame hardened parts which are air quenched are self tempered.2. for particular processes. However. alloy content. Designers should be aware that AGMA decreases load ratings for gears which do not have hardened roots. 5. 5. 5.7 Rating Considerations.80 0. In flame hardening.4 Tempering. if required.1 Applications. gearing is usually tempered at 300---375_F (149---191_C). In this case. For tooth by tooth hardening. if required.8 Specifications. Hardness can also be checked on end faces at flank and root areas. Gearing may be atmosphere cooled after carburizing to below approximately 600_F (315_C) and then reheated in controlled atmosphere to 1475---1550_F (802---843_C) and quenched. pitting resistance and root strength (bending). Carburized gearing is also used for (2) Depth of hardening obtained at each location specified when destructive tests are required. After carburizing for the appropriate time. and suitable core properties based on selection of the appropriate carburizing grade of steel.7. order. Gearing may be subsequently given a refrigeration treatment to transform retained austenite and retempered. The heat treater should submit the following information: (1) Surface hardness range obtained and the number of pieces inspected. power is lowered and travel is sometimes increased as the inductor approaches the end faces.07---0. if required. Carburized gear ratings are higher than the ratings for through hardened and other types of surface hardened gearing because of higher fatigue strength. a segment of a gear can be hardened and sectioned. Improved load distribution can be obtained by subsequent hard gear finishing. After quenching. An intermediate stress relief before final machining before carburizing may be used to remove residual stress from rough machining.70---1. When a gear cannot be sectioned. (2) Prior heat treatment. favorable compressive residual stress in the hardened case. and the number of pieces inspected. 5.10 percent carbon at the surface).3. the only positive way to check case depth is by sectioning an actual part. particularly at the root area.2 Case Depth Evaluation (Hardness Pattern). existence of a hardness pattern can be demonstrated by acid etching. gearing will usually be cooled to 1475---1550_F (802---843_C). hardness may be lower at the ends. High surface hardness. result in the highest AGMA gear tooth ratings for contact stress. 5. Case depth should be determined on a normal tooth section. Although it is not always practical. and direct quenched. In these instances. but actual depth cannot be accurately measured. (3) Hardening pattern required. Carburized gearing is used in enclosed gear units for general industrial use. particularly on larger gearing. normalize.2.9 Documentation. (5) Those areas where the surface hardness is to be measured and the frequency of inspection.2. Grit blasting is also occasionally used.Gear Materials and Heat Treatment Manual (3) Results of magnetic particle inspection. high speed and aerospace precision gear units and also large open gearing for mill applications. (6) Depth of hardening required and the location(s) at which the depth is to be obtained.3 Carburizing.2. NOTE: During tooth by tooth induction hardening. The drawing. (8) Tempering temperature. Gas carburizing consists of heating and holding low carbon alloy steel (0. Gear blanks to be carburized and hardened are generally preheated after the initial anneal by a subcritical anneal at 1100_F---1250_F (590---675_C). This is to prevent edge burning and cracking. using an appropriate superficial or micro---hardness tester.28 percent Carbon) at normally 1650---1800_F (899---982_C) in a controlled atmosphere which causes additional carbon to diffuse into the steel (typically 0. held at temperature to stabilize while maintaining the carbon potential. Conventional hard gear finishing (skiving and grinding) results in some sacrifice of beneficial compressive stress at the surface and substantially increases costs. normalize and temper or quench and temper to specified hardness before carburize hardening. 5. (7) Whether destructive tests are to be used for determining the depth of hardening and the frequency of such inspection. (Maximums may be specified for induction hardened parts). dimensional stability and possible grain refinement considerations. hardness pattern and depth can be checked by polishing end faces of teeth and nitric acid etching. ANSI/AGMA 34 2004---B89 . Carburized and hardened gearing is used when optimum properties are required. 5. or written specification should include the following information: (1) Chemical analysis range of the material or designation. This is done for machinability. high case strength. (4) Minimum surface hardness required. (9) Magnetic particle inspection. 5. 2 Materials. Surface hardness. Reference should be made to Table 4---1 for a list of typical carburizing materials and Appendix C for case hardenability considerations. at mid length of a test bar). present manufacturing problems. fatigue strength. Those testers which produce Diamond Pyramid or Knoop hardness numbers (500 gram load) are recommended.0 inch (180 mm) long 1 1/2 DP and coarser 3. ¢ 7. is considered satisfactory for determining effective case depth of ANSI/AGMA DP 35 2004---B89 . Maximum size of carburize gearing is currently in the 120 inch (3048 mm) diameter range. parts not designed for finishing or where finishing is cost prohibitive. thin sections. performance. but not necessarily the same heat. One inch (25 mm) diameter ¢ 2. Table 5---1 Test Bar Size for Core Hardness Determination Gearing beyond 80 inch (2032 mm) diameter is difficult to carburize due to the limited number of available furnaces for processing. but are not limited to. pitting wear resistance. when required. Selected areas of gearing can be protected from carburizing (masked) to permit machining after hardening. 5. case depth. ¢ 5. Specified finish operations after hardening depend upon accuracy and contact requirements for all applications. and economical considerations.25 inch (57 mm) D. The bar length should be 2---3 times the diameter.5 DP gearing should be mutually agreed upon. 5. chemistry. The size of the bar for coarser than 1. The recommended test bar diameter for bevel gearing is to be approximately equal to the inscribed diameter of the normal tooth thickness at mid face width. the following: toughness. cleanliness. in order that the hardness values obtained are representative of the surfaces or area being tested. an actual part may be sectioned for analysis. ¢ 3.0 inch (76 mm) D. ¢ 8. or can be machined after carburizing and slow cooling before hardening.Gear Materials and Heat Treatment Manual improved wear resistance. and core hardness can be specified to reasonably close tolerances.3 Control With Test Bars. Bars should accompany gearing through all heat treatments. complex shapes.3.0 inch (205 mm) long Test discs or plates may also be used whose minimum thickness is 70 percent of the appropriate test bar diameter. rack gears. The test bar should have minimum dimensions of 5/8 inch (16 mm) diameter by 2 inch (50 mm) long. Performance criteria include. Most of this large gearing requires tooth finishing (skiving and/or grinding) after carburizing and hardening. and the quality can be audited.0 inch (50 mm) long bar may be used for coarser pitch carburized gearing to 1.0 inch (76 mm) long 2 1/2 DP to less than 4 1/2 DP 2. bending strength. Test bars should be of the same steel type as the gear(s). Press quenching after carburizing can be used to minimize distortion. carburized helical and spur gearing to 4 1/2 DP.1 Case Hardness. Gearing which distorts and cannot be straightened without cracking. core hardness and core microstructure can be determined at the center of the round bar size shown in Table 5---1 according to diametral pitch. 5. Selection should be made on the basis of material hardness and hardenability.5 DP.0 inch (130 mm) long 1 1/2 DP to less than 2 1/2 DP 3. The minimum inscribed diameter on a test disc (or plate dimensions) should be a minimum of three times its thickness. notch sensitivity. When specified. Consideration should be given to evaluation of that portion of the case that is not removed during tooth finishing.3.25 inch (32. When measuring di- A section. and operational characteristics. Carburizing technology is well established and the available equipment and controls make it a reliable process. Test bars are used to show that the case properties and. including all post hardening treatments. and should approximate the inscribed diameter at mid height of the tooth cross section. core properties meet specifications. Material selection is an integral part of the design process. with a ground and polished surface (normal.3. BAR SIZE 4 1/2 DP and finer 1. Some gearing does not lend itself to carburize hardening because of distortion.5 inch (89 mm) D. When disagreement exists as to the properties obtained on the test bar and the parts.0 mm) D. Case hardness should be measured with microhardness testers which produce small shallow impressions.3. NOTE: Direct surface hardness readings (ASTM E18---79) or file checks at the tooth tip or flank will generally confirm the case hardness. (0. However. This type of inspection may be necessary for accurate micro---hardness readings near the surface. Section 3. one HRC point should be added to the 50 HRC effective case depth criterion (example. effective case depth should be measured at 52 HRC).05 to .10 mm) from the edge on a polished cross section of the tooth is more accurate. These variations should not fall below the minimum. 8627.Gear Materials and Heat Treatment Manual rectly on the surface of a case hardened part or test bar.3.002 to 0.0015 inch (0.3. Favorable compressive surface stresses are lowered.05 to 0. Carbon gradient can also be determined on the bar by machining chips at 0. When steels of high hardenability such as 4320. if secondary transformation products are present below the first several thousandths of the case.3. superficial or standard Rockwell A or C scale may be used. core hardness equals 47 HRC.005 inch (0.005 inch ANSI/AGMA 36 2004---B89 . 5.25 mm) beyond the depth at which 50 HRC is obtained.13 mm). depending on accuracy desired and depth of case. NOTE: Through carburized fine pitch teeth have several disadvantages.004 inch (.010 inch (0. Other instruments such as Scleroscope or Equotip are also used when penetration hardness testers can not be used.05 to .2 Core Hardness. For each one HRC point above 45 HRC.4 Case Carbon Content. if bar size has been previously correlated to the gear tooth section (refer to 5. NOTE: See definition of case depth of carburized components.Effective. The procedures used to prepare the cross sectioned specimen for case hardness (refer to 5. Low readings can be obtained when the indentor penetrates entirely or partially through the case. 5. and 3310 are used for fine pitches. Care should be exercised to maintain surface integrity during cooling or in tempering for subsequent machining. the high through hardening characteristics of the steel may prevent obtaining a hardness less than 50 HRC across the tooth section.038 mm) (TIR) before machining.3) should be used to prepare the specimen for case depth evaluation.3).3. giving consideration to the size of the specimen as discussed in 5. Care must be taken during grinding and polishing not to round the edge being inspected and not to temper or burn the ground surface. when core hardness is specified. When required. Surface carbon content may be determined from a round test bar by taking turnings to a depth of 0. Care should also be exercised in establishing the perpendicular to the mid tooth point when starting the traverse. 5. 9310. The case depth should then be determined in the following manner: Measure the base material hardness at mid tooth height at the mid face.3. Case depth in these instances may also be measured on a test bar.004 inch (. Excessive tooth distortion and a loss of core ductility can also occur. Effective case depth at roots are typically 50---70 percent of mid tooth height case depths. 4327.10 mm) below the surface and extend to at least 0.002 to 0. which results from the steel melting practice. Microhardness inspection 0. Usually an interval of 0. can cause variations in core hardness during testing with a microhardness tester.3. Spectrographic techniques have also been developed for this purpose. core hardness may be determined by any hardness tester.004 inch (. The microhardness traverse should be started 0. Test specimens must be clean and machined dry.10 mm) below the surface.3. Consideration must be given to the case depth relative to the depth of the impression made by the tester.002 to 0.002 to 0. direct surface checks will not necessarily indicate their presence. Grinding in steps through the case would be used with spectrographic techniques.3. and tips may be 150 percent of mid tooth height case depths.01 inch (.05 to .3. 4820.3. Care must be taken to ensure that the turnings are NOTES: See definition of core hardness. Occasionally banding.25 mm) increments through the case. Section 3. Parts of this type should be carefully reviewed for case depth specifications and for use of lower hardenability steels such as 4620 and 8620. Bar should be straightened to within 0.3 Case Depth --.13 mm) is used. Microhardness tests for surface hardness should be made on a mounted and polished cross---section at a depth of 0. Test specimens should be carburized with the parts. and accuracy of temperature recording and control instruments. (1) Material. 5.3. It will result in reduced hardness if the carbon content falls below approximately 0. close temperature control. the heat treater should be given the following as a minimum: NOTE: Caution should be exercised in the use of refrigeration treatment on critical gearing. (3) Case microstructure. are shown in Table 5---3. which can be obtained from some typical carburizing grades of steel and good agitated oil quenching. When additional characteristics are required. The microstructure may be determined on a central normal section of the test bar or tooth. The refrigeration treatment may vary from 20_F (---7_C) to ---120_F (---84_C). Furnaces should be capable of maintaining a carburizing atmosphere with controllable carbon potential. Instrumentation for ANSI/AGMA 37 2004---B89 . but other approved methods may be used. typically 0. Hardness in this area will be substantially lower.60 percent carbon.60 percent. Microstructure will vary with the core hardness as related to steel hardenability. (1) Temperature Control. (2) Atmosphere Control. Surface decarburization as defined for carburized gearing is a reduction in the surface carbon in the outer 0. (3) Subzero Treatment (Retained Austenite Conversion Treatment).5 Carburizing Process Control. when the peak carbon content is subsurface. 5. This is characterized by an increase in carbon content with increasing depth. for example. continuous atmosphere control is preferred. Carbide networks should be avoided whenever possible as they tend to reduce fatigue strength of the material. (3) Surface hardness range. to diffuse and break up the excess carbide.5 Microstructure. section size and quench severity.13 mm) below the specified minimum.3. the following additional items may be specified in whole or part: (4) Carbide Control. (6) Areas to be free of carburizing by appropriate masking by copper plating or use of commercial stop---off compounds. 5. (4) Surface carbon content. Approximate minimum tooth core hardness. Furnace equipment with temperature uniformity. (2) Case depth range (refer to Table 5---2).005 inch (. Microcracks can result which can reduce fatigue strength to a moderate degree. parts should be reheated to typically 1650_F(900_C)in a lower carbon potential atmosphere. but may not show discernible ferrite. To minimize microcracking. Controls should be checked and calibrated at regular intervals. (2) Core microstructure. (5) Decarburization. preferably mounted. Use of refrigeration may require agreement between the customer and supplier. When high surface carbon results in a heavy continuous carbide network in the outer portion of the case. it may be necessary to refrigerate the parts to transform the retained austenite to martensite. after being properly polished and etched. (1) Core hardness. Precision carburizing requires close control of many factors including: Gross decarburization can be readily detected microscopically as a lighter shade of martensite and clearly defined ferrite grains.3. Partial decarburization will result in a lighter shade of martensite.3. parts should be tempered before and after refrigeration. (5) Subzero treatment. When the surface hardness is low due to excessive retained austenite in the case microstructure. To aid in obtaining the above characteristics.Gear Materials and Heat Treatment Manual free of any extraneous carbonaceous materials prior to analysis.4 Specifications. 1.3 --.2.0.2 --.045 --.0.2.090 0.094 Range of Normal Diametral Pitch 17. Use of carbonitriding is more restricted than carburizing.060 0.050 0.2.251 0.026 --.5 7.145 0.0.25 1.157 0.080 0.4 Carbonitriding.8 --.098 0.040 0.2 --.200 --. Specified case depths are usually from 0.0.0.76 mm) maximum.1. One of the 38 2004---B89 .047 1. heavier case depth than shown in table may be required.600 --.120 0.3 on carburizing will generally apply to carbonitriding.030 0.676 1. For very heavily loaded coarse pitch ground thread worms.131 0.090 0.785 0.4 5 Worms with Ground 7 Threads 0.140 0.105 0.060 0.2. It is limited to shallower cases for finer pitch gearing since the process must be conducted at lower temperatures than carburizing.3 --.035 --.1.180 0.400 1.5 2.075 --.8.200 1.860 0.230 --.230 0.0.628 0. 2 Gears with thin top lands may be subject to excessive case depth at the tips.025 0. Shallower case depths are generally specified for carbonitriding than is usual for production carburizing.075 --.1.060 --. Un---ground worm gear cases may be decreased accordingly. detailed studies must be made of the application.676 --.6 --. 5.4.0.5 8.4 to determine mm equivalent.1 Applications (Advantages and Limitations).3 --.393 0.5 3.5 to 5 percent anhydrous ammonia is added to the carburizing atmosphere when carbonitriding. Typically carbonitriding is carried out at lower temperatures.105 0.698 0.0.090 0.180 --. .13.7 --.3 4. Deep case depths require prohibitive time cycles.0. Helical Bevel & Mitre 6 0.5 6.300 0.090 0.060 0.976 --. Land width should be calculated before a case is specified.480 --.0.1 & less Range of Normal Circular Pitch 0. ANSI/AGMA Normally 2.5 --.003 to 0.200 1.75 2.0.075 --.3.030 0.060 0.0.028 1.2.728 0.0.5 --.030 0.480 0.090 0.Gear Materials and Heat Treatment Manual Table 5---2 Typical Effective Case Depth Specifications for Carburized Gearing Normal Diametral 1 Pitch Normal Tooth 2 Thickness 16 14 12 10 8 7 6 5 4 3.300 0.75 0.055 0.75 1.828 2.860 --.5 10.040 --.112 0.075 --.075 --.728 --.25 2.200 --.13.1 --.0.025 --.105 0.0.0.0.090 0.0 1.055 0.020 0.571 0.025 0.020 0.897 1.070 0.205 0.1 & less 1.020 --.400 --.070 0.080 0. 3 Case at root is typically 50---70 percent of case at mid tooth.015 0.050 0.828 & more 2.9 --.170 0.020 --. 4 The case depth for bevel and mitre gears is calculated from the thickness of the tooth’s small end.0.0.125 0.075 --.449 0.1.045 --.198 0. with noted exceptions.2.314 0.1.090 0.3 1.1. 5 For gearing requiring maximum performance.1. The purpose of this Section is to establish methods for specifying carbonitrided gearing.0.8 2.5 --. 5.040 0.0.045 --.300 --.224 0. All other pitch measurements should be converted before specifying a case depth.075 --.6 1.010 0.030 inch (0.060 0.075 --.030 0.180 --.4. Information in 5.040 --.523 0.3 2.076 to 0.5 --.1.090 0.090 1 All case depths are based on normal diametral pitch.050 0.0.0.155 0.075 --.040 0. Its effect on steel is similar to liquid cyaniding and has replaced cyaniding because of cyanide disposal problems. multiply values given by 25.1.256 1.090 0.5 --.6 2.2.600 0.0.0 0.1.1 1.070 0.428 --.7.026 --.7 --.9 1.10.010 0.090 0.7 3.020 0.075 --.325 & more Effective Case Depth (inches) to RC 50 Spur.480 0.205 3.6 --.370 --.570 2.090 0.0 2.0.2 5.7 17.170 ----------------------------------------- 0.090 0.025 0.075 0.370 0.5 --. loading and manufacturing procedures to determine the required effective case depth.6.5.080 0.2 2.040 0.1 3.370 --.3.5 1. 7 Worm and ground---thread case depths allow for grinding. 6 To convert above data to metric. and for shorter times than gas carburizing.400 2.400 1.0.976 1.0. For further details refer to AGMA 2001---B88. 1550---1650_F (843---899_C).7 13.0. and molybdenum. which has had a quench and temper pretreatment and is usually finish machined.Gear Materials and Heat Treatment Manual spection of nitrided gearing. This section covers the selection and processing of materials. 1022. During nitriding.0 hours in an aerated salt bath or atmosphere. Steels containing chromium.5 to 4. along with lower alloy steels. These processes result in a wear resistant surface layer of 0.5. vanadium. 5. 5. aluminum. nitrogen atoms are absorbed into the surface to form hard iron and alloy nitrides. depending upon application. 5. are required in order to form stable nitrides at the nitriding temperature. thus reducing tooth growth and distortion. the Nitralloy grades. maximum hardness will typically be 8---10 points higher than the minimums listed. Conventional gas nitride hardening of gearing. Aluminum containing grades such as Nitralloy 135 and Nitralloy N will develop higher case hardness.2 Materials. microstructure. due to inherent brittleness of the case.00 percent.5 Nitriding. Nitrided gears should not be specified if shock loading is present.5) should not be confused with aerated salt bath nitriding or nitrocarburizing in which nitrogen is absorbed into the steel surface at approximately 1060_F(570_C) for short cycles of 2.38---0. The practical limit on case depth is about 0.001 inch (0. 4022. result in the lower core hardness mentioned previously. means of specifying.4. hardnesses obtainable. and inANSI/AGMA 39 2004---B89 .50 mm) which enhances fatigue strength.5. The carbonitrided case has better wear and temper resistance than a straight carburized case. with a nitrogen compound layer to a depth of 0.treatments. which requires a thorough stress analysis (for other than wear applications) of the effectiveness of the case for coarse pitch gearing.3 Pre--. 4118 and 8620 steels are used for carbonitriding. advantages of carbonitriding is better case hardenability in lower alloy or plain carbon steels. 4150. Case depth. carbonitriding may not be applicable. and steels with chromium contents of 1. 1 Depending upon the Jominy curve of the particular material. Parts to be nitrided must be quenched and tempered to produce the essential- 5. involves heating and holding at a temperature between 950---1060_F (510---571_C) in a controlled cracked ammonia atmosphere (10 to 30 percent dissociation). The purpose of this section is to provide information. and when through hardened gears do not provide sufficient wear and pitting resistance. Typically carbon and low alloy steels such as 1018. for carbonitrided parts can all be specified and evaluated as prescribed in the section for carburized gearing. The advantages and limitations as described herein should be fully understood before specifying carbonitriding for industrial gearing.25 mm) are generally specified as total case depth. 5.0 mm) maximum. hardness. Case depth is specified and measured as effective or total. Use of H band steel is the normal method of hardenability control. and definitions and inspection of depth of hardening.1 Applications.00 to 3. Typical steels suitable for nitriding are 4140.2 Materials.010 inch (0. These facts. 4340.3 Specification and Inspection.025 mm) or less. However. 5. if higher core hardness and deeper case depths are required for bending resistance. Nitride hardening can also be achieved with the ion nitriding process.5. Cases shallower than 0. high hardness cases can withstand applied loads.4.015---0. Nitrided gears are used when gear geometry and tolerances do not lend themselves to other case hardening methods because of distortion.040 inch (1. Carbonitriding can be used to minimize distortion in finer pitch gearing because lower austenitizing and quenching temperatures can be used along with less severe quench techniques and still achieve hardness. etc. Nitrided gears are used on applications where thin. 1117.020 inch (0. Table 5---3 Approximate Minimum Core Hardness of Carburized Gear Teeth Grade Hardness HRC Minimum Pitch 2---3 3316 9315 3310 9310 4820 8822 4320 8620 4620 1020 34 32 31 28 27 25 23 18 ----- 1 4 5---6 7 & UP 36 34 33 31 33 30 27 24 18 14 37 36 35 33 35 32 30 26 22 16 38 37 36 34 36 34 33 28 25 18 NOTE: The above processes (5. either singularly or in combination.4 and 5. the newer ion nitriding process should be considered. causing distortion. If distortion control is very critical. 5. The nitriding process affects the rate of nitrogen adsorption and the thickness of the resultant brittle white layer on the surface.1 Material Selection. The ion nitride process uses ionized nitrogen gas to effect nitrogen penetration of the surface by ion bombardment. The amount and direction of growth or movement should be determined for each ANSI/AGMA 40 2004---B89 . A two stage nitriding process (two temperatures with increased percent of ammonia dissociation at the second higher temperature) generally reduces the thickness of the white layer to 0.Gear Materials and Heat Treatment Manual ly tempered martensitic microstructure required for case diffusion. Selection of the grade of steel is limited to those alloys that contain metal elements that form hard nitrides as discussed in 5. or by coating with proprietary paints specifically designed for this purpose.026 mm) maximum. Nitriding over decarburized steel causes a brittle case which may spall under load. which produces a brittle case prone to spalling.13 mm) thick. 5. This must be considered when selecting tempering or stress relieving temperatures. and time of nitriding. Nitrogen adsorption in the steel surface is affected by oxide and surface contamination. part by dimensional analyses both prior to and after nitriding. The white layer thickness is also dependent upon the analysis of steel. 5. degree of ammonia dissociation.5. This should be avoided by tempering at approximately 50_F (28_C) minimum above the intended nitrided temperature after quenching.5. 5. surface hardness. Sharp corners or edges become brittle when nitrided and should be removed to prevent possible chipping during handling and service.4 Nitriding Process Procedures.0007 inch (0.018 mm) minimum thickness. residual stresses from quench and tempering may be relieved at the nitriding temperature. However. Nitriding can be accomplished at lower temperatures with ion nitriding than those used for conventional gas nitriding. tin plate 0.008 to 0.5. nitrided hardness is lessened appreciably by decreased core hardness prior to nitriding.001 inch (0.5. Microstructure must be free of primary ferrite. core hardness and material selection constraints. Where it is desired to selectively nitride a part.5. intermediate stress relieving after rough machining at 25---50_F (14---28_C) below the tempering temperature may also be required prior to finish machining to relieve machining stresses before nitriding. temperature. The process can provide flexibility in determining the type of compound produced. nitrided surfaces subject to stress should be free of decarburization. The nitriding process will cause a slight uniform increase in size. such as is produced by annealing and normalizing.0003 to 0.5 Specific Characteristics of Nitrided Gearing. In order to minimize distortion of certain gearing designs.2. Nitriding does not lend itself to every gear application. Therefore. such as blind holes and small orifices. Core hardness obtained in the quench and temper pretreatment must provide sufficient strength to support the case under load and tooth bending and rim stresses. The nitride process is restricted by and specified by case depth.0005---0.5. Core hardness requirements limit material selection to those steels that can be tempered to the core hardness range with a tempering temperature that is at least 50_F (28_C) above the nitriding temperature.005 inch (0.5.013---0. Variables in the nitriding process are the combined effects of surface condition. In alloys such as series 4140 and 4340 steels. The process can also be tailored to better control nitriding of geometric problems.2 Core Hardness. In order to guarantee nitrogen adsorption it may be necessary to remove surface oxidation by chemical or mechanical means. the surfaces to be protected from nitriding can be plated with dense copper 0. Approximate core hardness Nitrided parts will distort in a consistent manner when all manufacturing phases and the nitriding process are held constant. thin case as well as higher core hardness.3 Surface Hardness. 28 30 32 34 A test bar. obtained on typical nitrided steels are as follows: Steel Type Minimum Surface Hardness. Sectioning of an actual part to determine case depth need only be performed when the results of the test bar are cause for rejection. disc or plate section. 5.5. The production quantity of any gear must be sufficient to justify the cost of capital equipment and set---up to surface hardened by either process.5. Surface hardness will also increase with increasing nitride case depth. Lower core hardness will result from less alloy. including laser heat treating and electron beam heat treating. The test section must be of the same specified chemical analysis range and must be processed in the same manner as the parts it represents.5.5. 5. Use of electron beam heat treating for gear 1 Converted to HRC 2 British and German analyses. Both laser and electron beam surface hardening of gears are selective in nature and are generally applied to gears smaller than those routinely hardened by other methods. larger section size.6 Other Heat Treatments. respectively NOTE: Data infers a 269HB minimum core hardness. ANSI/AGMA 41 2004---B89 . HRC 4140 4150 4340 Nitralloy 135 Case depth should be determined using a microhardness tester. reduced quench severity and a greater degree of martensite tempering. At least three hardness tests should be made beyond the depth at which core hardness is obtained to assure that the case depth has been reached. Surface hardness and core hardness will influence the design’s minimum required case depth. or the surface hardness of the part(s) is not within 3 HRC points of the surface hardness of the test bar. Gearing may also be heat treated by other means. Thermal energy for heating the surface to the austenitizing temperature is supplied by either the laser (light amplification by stimulated emission of radiation) or electron (kinetic energy of electrons) beam.Gear Materials and Heat Treatment Manual most specifications only specify a minimum case depth requirement.5. (1) (2) (3) (4) (5) Material grade Preheat treatment (see 5.5. can be used for determining case depth of nitrided parts. The specified case depth for nitrided gearing is determined by the surface and sub---surface stress gradient of the design application. if required (6) Areas to be protected from nitriding by masking.5. if required (7) Nitriding temperature (8) Metallurgical test coupons Table 5---4 Approximate Minimum Surface Hardness --. Parts which are to be nitrided should have the following specified: Approximate minimum surface hardness which can be obtained on nitrided steel is shown in Table 5---4. Since the diffusion of nitrogen is extremely slow. Lower core hardness results in a microstructure which causes a lower surface hardness nitrided case. These processes are not available from commercial heat treaters.4 Case Depth.2) Minimum surface hardness Minimum total case depth Maximum thickness of white layer. Surface hardness is limited by the concentration of hard nitride forming elements in the alloy and the core hardness of the gear. for example 1/2 to 1 inch (13 to 25 mm) diameter with a length 3 ¢ the diameter.6 Specifications. 5. while the underlying mass provides the heat sink to quench harden the surface. since it limits the ability to form high concentration of hard metallic nitrides. Lower core hardness does not support the hard.Nitrided Steels Steel Type 4140 4150 4340 Minimum Surface Hardness R15N HRC! 85 48 85 48 84 46 Nitralloy (contains Al) 90 60 2 1/2 percent Chrome (EN 40B & 40C and 31CrMoV9)@ 89 58 5. such as quantity production for the automotive industry. to full gear tooth contours. Section size modification may be required along with added stock for grinding or machining after heat treatment. parts can easily crack if made of high---carbon. There are a variety of quenchants to choose from such as: oil. hardness. The temperature of a water quenchant is more critical than that of an oil. Each quenchant should be used within its appropriate range of temperature. Quench cracks usually originate at sharp corners or substantial section size changes. Quenching the structure to martensite prior to tempering results in steel growing in size. teeth is restricted. mechanical properties and residual stress distribution. Each variety is available with a wide range of quench characteristics. 5. result in less distortions than processes that require liquid quenching. The quenching process is one of the major operations that influences the microstructure. The main factors which control the quench rate are: part geometry. polymer. Tolerancing must consider these changes. especially if improperly tempered or stress relieved. The degree and uniformity of agitation greatly influences its rate of heat removal.8. Tempering of the hardened structure reduces the volume. Thermal processes such as annealing. which do not require liquid quenching. Distortion is due to mechanical and thermal stresses and phase transformation. It is good practice to immediately temper after quenching if quench crack problems are a concern. for flank and root contour surface hardening of gear teeth. even with perfectly uniform sections. The geometry will affect how quickly and uniformly the quenchant will circulate around the part. The part design and manufacturing process must consider movement during heat treatment. degree of agitation and quench temperature.Gear Materials and Heat Treatment Manual por bubbles and restrict the flow of quenchant should be avoided. The temperature of the quenchant may affect its ability to extract heat. Delayed quench cracks can occur hours or days after quenching. 9th Edition. however. Distortion of gearing during heat treatment is inevitable and varies with the hardening process. The designer’s or heat treater’s responsibility is to select the quench variables to obtain the required properties in the gear. and is better suited for flat than curved surfaces. 5. normalizing. water. Quenched and tempered gearing changes size and distorts due to mechanical and thermal stresses and microstructural transformations. Process variables and design considerations have a significant effect upon the amount of distortion. The quench needs to be fast enough to avoid secondary transformation products.7 Quenching. Agitation is externally produced movement of the quenchant past the part. brine and gases. Table 5---5 associates some material grades and their normally used quenchants. The preferred microstructure after quenching is primarily martensite. Dimensional changes of gearing resulting from heat treatment occur principally when steel is quenched. but slow enough to reduce distortion and avoid cracking. assuming the gear has been properly heated before the quench. Pockets which trap va- ANSI/AGMA 42 2004---B89 . Agitation can be provided by propellers or pumps in the quench tank or by moving the parts through the quenchant. 5. however. molten salt.8 Distortion.2 Quenching and Tempering. Dual laser beam optics have been developed. This is true because the stream of electrons must have line of sight access to the surface to be hardened with a beam impingement angle of at least 25 degree (25---90 degrees impingement angle range). High induced stress can result in quench cracking. These changes occur in both quenched and tempered and surface hardened gears. high---hardenability steels and the quench is too severe. Reference should be made to the ASM Metals Handbook. and diffusion controlled surface hardening processes such as nitriding. The material hardenability will determine how severe the quench has to be for a particular part geometry. as well as other modifications of heat treatments applied to gearing. Quenching is the rapid cooling of steel from a suitable elevated temperature. However. but the combined effects of quenching and tempering still result in a volume and size increase. Volume 4 on Heat Treating for additional information on laser and electron beam heat treating. type of quenchant.8. 5.1 Causes. Gear Materials and Heat Treatment Manual Table 5---5 Commonly Used Quenchants for Ferrous Gear Materials Material Grade Quenchant Remarks 1020 Water or Brine Carburized and quenched with good quench agitation. Unalloyed or low alloy irons require oil or polymer. however. Hot oil is often used. 1141 1541 Oil or Polymer Good response in well agitated conventional oil or polymer. Some loss in core hardness will also result from hot oil quench. thin sections or sharp corners can represent a crack hazard. Oil is sometimes used and air quench can be applied for flame hardening with proper equipment. Hot oil should be considered in these cases. parts are often removed warm and tempered promptly after quench. Smaller sections can be processed in well agitated oil. air quench can be used for flame hardened parts. Crack sensitivity applies also to flame or induction hardened parts with high concentration polymer being the usual quenchant. 1045 4130 8630 Water. Large sections normally require water or low concentration polymer. hot oil at 275---375_F(135---190_C) may be used to minimize distortion. ANSI/AGMA 43 2004---B89 . Polymer or Air If conventional oil is used. Oil or Polymer Type of quenchant depends upon chemistry and section size. conventional oil can be used. 9310 These are high hardenability steels which can be crack sensitive in moderate to thin sections. 3310 Oil Carburized and quenched in hot oil at 275---375_F (135---190_C). High concentration polymer should be used with caution. For finer pitched gearing. Induction or flame hardened parts normally quenched in polymer. In this section parts and flame or induction hardened surfaces can be crack sensitive. With proper equipment. 4118 4620 8620 8822 4320 Oil Carburized and quenched in well agitated conventional oil at 80---160_F(27---71_C) is normally required. 4140 4142 4145 Oil or Polymer Same as above. 4150 4340 4345 4350 Oil or Polymer Gray or Ductile Iron Oil. This is the preferred quench. High alloy irons can be air quenched to moderate hardness levels. Quench media depends upon alloy content. In larger sections. temperature and amount of agitation. etc.3). (5) Carburizing temperature and temperature prior to quenching. Close control is.1 Carburized Gearing. case depth.080 inches (2 mm) or greater. however. (b) Side faces become warped. amount of bowing or radial runout is often confined to journal diameters and shaft extensions for integral shaft pinions. (4) Carbon potential of the carburizing atmosphere. uneven cooling.8. amount of retained austenite. Selective surface hardening of gear teeth by flame and induction hardening results essentially in only distortion of the teeth because only the teeth are heated and quenched. compared to profile hardened tooth patterns. and a second stress relief prior to finish machining may all be necessary to keep the pinion dimensionally stable during finish machining. (3) Fixturing techniques in the furnace and during quenching. Distortion must be minimized. Pinions become bowed. Principal variables affecting the amount of growth.8.8. straightening. required. NOTE: Direct quenching generally results in less distortion than slow cooled. and residual stress include: (1) Geometry. Once a component is designed to minimize distortion. whichever is less.3. Stress relief temperature is dependent upon specified hardness and temper resistance of the steel. Distortion is not limited to gear teeth. Higher hardenability increases growth and distortion. processing techniques should be optimized to make distortion consistent. (6) Time between quench and temper for richer alloys. (2) Pinions.007 inch (0. Distortion results from microstructural transformation. Lack of repeatability is due to the greater number of variables which affect distortion. when tooth accuracy requirements dictate.4. Modified methods of quench hardening. Amount of distortion increases with case pattern depth and increases as more of the tooth cross section is hardened. redesign of components may be required to reduce distortion. Normally.) considerations.18 mm) per tooth surface or 20 percent of the case depth. At times. etc. In some exceptional instances. or casting) have sufficient stock provided so distortion can be accommodated by machining. controlled and made predictable to minimize costly stock removal (lapping. such as carbon content. skiving. ANSI/AGMA Stock removal by grinding after carburize hardening should be limited to approximately 0. (8) Resultant metallurgical characteristics of the case. 5. reheated and quenched gears. or grinding). and residual stress (from thermal shock. with the amount of bowing increasing with higher length/diameter ratios and smaller journal diameters. reduces distortion and forms a modified hardened structure at higher quenchant temperatures than those conventionally used (refer to 4. This stress is balanced by corresponding residual tensile stress beneath the case. Distortion of carburized gearing makes it one of the least repeatable of surface hardened processes. and exhibit runout.3 Surface Hardened Gearing. such as austempering of ductile iron. carbides. barstock. Exception may be made for coarser pitch gearing with cases 0. (2) Hardenability (carbon and alloy content) of the base material. Sequence of manufacture is dependent upon design considerations and the temperature used for stress relief. Surfaces other than the tooth flanks and roots may tolerate greater stock removal. High L/D ratio pinions may require straightening and a thermal stress relief prior to finish machining. (7) Quenchant type. therefore. rough machining. rough gear blanks (forging. thermal stress relief. 44 2004---B89 . when the entire gear is heated and quenched as with carburizing. 5. distortion.Gear Materials and Heat Treatment Manual Distortion of quenched and tempered gearing occurs generally as follows: (1) Gears (a) Outside and bore diameters grow larger and go out of round. Transformation in the case results in growth which sets up residual surface compressive stress. providing gears are properly cooled from the carburizing temperature to the quench temperature before hardening. may cause collapsing of the rim section over the holes. (5) Bowing of the integral shaft pinions. Teeth may also be both crown cut and chamfered. The recess is provided to enable clean---up grinding of the rim and hub end faces after hardening. (3) Eccentricity (radial run---out) of gears and their bores is dependent upon how they are fixtured in the furnace. Masking can also be used for ease of straightening. (4) Taper across the face (tapered teeth). where the adjacent diameter is larger than the root diameter. designed with moderate recess on both sides of the web section. 90 degrees apart. CANTILEVER PINION BLIND ENDED TEETH HIGH L/D RATIO CONCENTRIC BLANKS Fig 5---4 General Design Guidelines for Blanks for Carburized Gearing ANSI/AGMA 45 2004---B89 . which often requires an increased helix angle to be machined into the element prior to carburizing (more prevalent in pinions). Journals may be required to be masked in order to prevent carburizing and then be finish machined after hardening with sufficient stock for clean---up. to reduce the weight or provide holes for lifting. distort less. bore taper and “hour---glassing” of the gear bore can occur due to non---uniform growth of teeth across the face and non---uniform shrinking of the bores. Integral shaft pinions should. present problems from both distortion and finishing standpoints. be hung or fixtured in the vertical position (axes vertical) to minimize bowing. whenever possible. with teeth on the end of the shaft. (5) High length/diameter ratio pinions distort more. (2) End growth on gear teeth at both ends of the face due to increased case depth (carburizing from two directions. Web support section thickness under the rim is recommended to be not less than 40---50 percent of the face width for precision gears. (1) Larger teeth (lower DP) distort more. (4) Holes in the web section close to the rim. (6) Cantilever pinions. Teeth on larger diameter. and “blind ended” teeth on pinions. (3) Radial web support section under the rim should be centrally located. Near solid “pancake” gear blanks. (2) Rim thickness should be the same at both end faces. Teeth are often crown cut prior to hardening to compensate for reverse crown or are chamfered at the ends of teeth. smaller face width gears may exhibit “helix wind---up” after hardening.Gear Materials and Heat Treatment Manual General design considerations of carburized gearing related to distortion include the following (refer to Fig 5---4): Distortion of carburized gearing also exhibits the following typical characteristics (refer to Fig 5---5): (1) Reduction in tooth helix angle (“helix unwind”). followed by improved quench action for the same reason) may appear as reverse tooth crowning on narrow face gearing. the entire tooth cross section is often hardened to the specified depth below the roots of teeth. and enable subsequent machining. Therefore. and induction hardening.3 Nitrided Gearing. For high bending strength applications. nitrided gear teeth are not generally required to be During both spin flame and spin induction hardening. (2) Increased growth of the teeth (greater than for carburized gearing) because the entire tooth cross section may be hardened in finer pitch gearing. as with carburized pinions.3. Flame and induction hardened gearing generally distort less than carburized gearing because only the teeth are heated and subsequently quenched. may be press quenched to minimize distortion. Spin flame hardening involves more manual set---up factors. and are not quenched.3. depending on size and face width. gas flows. is done before machining and nitriding. Prior quench and temper heat treatment. which results in distortion. or fixtured horizontally (individually or stacked) to minimize distortion. CAUTION: Deep spin hardening of gear teeth may cause excessive tooth growth and may affect bore size. (3) Crowning or reverse crowning of the teeth across the face dependent upon the heat pattern. compared to carburize. However. spin flame hardening can be engineered with special flame heads and fixtures for required control. Distortion of the teeth from spin induction hardening is often considered more repeatable than with spin flame hardening. (4) Taper of teeth due to varied heat pattern and case depth across the face. because of fewer human error factors involved during machine and inductor set--ups with induction hardening.2 Flame and Induction Hardened Gearing. as occurs during carburizing. 5. flame. Parts are also not heated above the transformation temperature or previous tempering temperature of the steel during nitriding. Distortion increases as a greater cross---section of a tooth is hardened. 5. it is not desirable to have the hardening pattern terminate in the roots of the teeth because of residual tensile stress considerations. flame or induction hardening.8. which include positioning of the flame. ANSI/AGMA 46 2004---B89 . Spin flame and spin induction hardening generally produce the following distortion characteristics: (1) Helical unwinding of the gear teeth. Contour induction hardening of tooth profiles produce less distortion and growth than spin hardening methods. Nitriding of gearing results in less distortion.Gear Materials and Heat Treatment Manual STRAIGHT HELICAL UNWIND TAPER HOURGLASSING BOWING END GROWTH (REVERSE CROWN) ECCENTRICITY Fig 5---5 Typical Distortion Characteristics of Carburized Gearing Gears may be fixtured vertically through the bores or web holes on a support rod (axes horizontal). Larger ring gears are positioned horizontally with sufficient stock for clean---up of the teeth. Thin section gears. Crowning is more desirable from a tooth loading standpoint.8. etc. Bores and web sections can be masked to prevent carburizing. such as bevel ring gears. in the same manner as the part will be peened. This type of equipment is generally used for high performance gearing. There are three classifications of Almen Strips. to minimize the number of fragmented particles caused by fracturing of the shot. nozzle type equipment is generally preferred because of the ability to vary the angle of shot impingement and. Contact fatigue strength may also be improved in some instances by shot peening. achieve more uniform intensity along the toothform. hardened steel strip called an Almen Strip.031 inch (0. Figure 5---6 also shows the dimensions for the Almen strips and holding fixture. 5. Machinery used for shot peening should be automatic and provide means for propelling shot by air pressure or centrifugal force against the work. Coverage refers to the percentage of indentation that occurs on the surface of the part.04 mm) depending upon size.2 Shot Control.051 inch (1. When these limits are reached. 5.2.9. should be provided. or both. This stress may improve the bending fatigue strength of a gear tooth as much as 25 percent. An intensity determination must be made at the beginning.9. 5.Gear Materials and Heat Treatment Manual ground or lapped after hardening to meet dimensional tolerance requirements. Periodic inspection of the shot is required to control shot size and shape within specification limits.1 Intensity Control. 0. therefore.0. a high degree of process control is essential to assure repeatability.8 mm). which have thicknesses of 0.0938 inch(2. Shot peening should not be confused with grit and shot blasting. gearing can be rough machined and stress relieved at 50_F(28_C) below the prior tempering temperature to relieve rough machining residual stress prior to finish machining and nitriding.4 mm) respectively.0015 inch (0.025 mm). One hundred percent coverage is de- Regardless of the type of equipment used.2. which are cleaning operations.0.2. N. Because it is difficult to directly measure the effects of shot peening on a part. Mechanical means for moving the work through the shot stream by either translation or rotation. the strip will bow convexly on the peened surface. Also. Surfaces can also be masked for subsequent machining. Machinery must be capable of consistently reproducing the shot peening intensity and coverage required.9. although centrifugal wheel equipment is often used for very high volume production. Shot size and shape must be carefully controlled during the shot peening process. Bores size may shrink up to 0. Shot peening is a cold working process performed by bombarding the surface of a part with small spherical media which results in a thin layer of high magnitude residual compressive stress at the surface. 5. The strip is held flat on an Almen block placed in the representative location during the peening operation. A.1 Equipment. ANSI/AGMA 47 2004---B89 . as a result of lower mass.9. hardened and tempered to 40---50 HRC.0015 inch + ( --. 5. it may be used either to salvage or upgrade a gear design.9.2 Process Control. the shot should be classified and separated to restore size and shape integrity as shown in MIL---S---13165B. Intensity refers to the kinetic energy with which the peening media strikes the part. The amount of bow is measured in inches with a gauge and is called the arc height (see Fig 5---6). During nitriding. These fragmented particles can cause surface damage. and C.0005---0. at intervals of no more than four hours and at the end of each production run. Flatness tolerance is + --. This energy controls the depth of the peening effect. outer surfaces grow approximately 0. Strips are SAE 1070 cold rolled spring steel. When close tolerances are required. Whenever a processing procedure is developed for a new part. When released from the block. Bearing diameters of shaft extensions are often ground after nitriding with only minimum stock provided.3 mm) and 0. but quantitative data to substantiate this condition is limited.001 inch (0. 5. This is accomplished by shot peening several strips at various times of exposure to the shot stream and plotting the resulting arc heights. fragmented shot particles will lengthen the time to reach a specified peening intensity. For optimization of shot peening of gears. Because the process increases bending fatigue strength.9 Shot Peening.04mm). the gear must be rotated on its axis while exposed to the shot stream.013---0. It is becoming an accepted practice to specify shot peening on carburized and other heat treated gears. Saturation is defined as that point at which doubling the time of exposure will result in no more than a 10 percent increase in arc height. It is measured by shot peening a flat.3 Coverage Control. an intensity curve must be developed which establishes the time required to reach peening saturation of the Almen strip. glass bead. may also be used.02mm) --+ 0. Most shot peening of ferANSI/AGMA rous materials is accomplished with cast steel shot. SAE---J808a---SAE HS84.001 in (2. 300 percent. Shot type and size selection depends upon the material. Coverage must be related to the part.75 in (19.4mm) + 0. Shot types available are cast steel (S).051 + ---0. not the Almen strip.015 in (76+ --. The following sections describe items that the designer should include in a shot peening specification.5 in (38.38 0.001 in (1.9 to 19.).30 0.9.0 mm) HOLDING FIXTURE PEENING TEST (a) STRIP REMOVED.3 Design Consideration. In the latter process. and ceramic.0 + ---0. etc. A commonly referenced shot peening specification is MIL---S---13165B which identifies materials. The SAE Manual on Shot Peening. procedures. The actual part must be examined for complete coverage in all areas specified to be shot peened. the harder shot 48 2004---B89 .02mm) --- A STRIP PEENING NOZZLE C STRIP 0. and geometry of the part to be peened. Cast steel shot is available in two hardness ranges: 45---55 HRC.001 in (0.Gear Materials and Heat Treatment Manual fined as uniform dimpling of the original part surface as determined by either visual examination using a 10X magnifying glass or by using a fluorescent tracer dye in a scanning process. quired to obtain multiples of 100 percent coverage is that multiple times the time to reach 100 percent coverage (200 percent. full coverage has been achieved when no traces of the dye remain when viewed under ultraviolet light.3.9. 5. and quality control requirements for effective shot peening. conditioned cut wire (CW).79 0.0938 + ---0.750 in (18.9. When peening gears higher in hardness than 50 HRC. hardness. A minimum of 100 percent coverage is required on any shot peened part.1 Governing Process Specification. 5. The time re- 3. and 55---62 HRC.02mm) --- N STRIP + 0.2 Shot Size and Type.1mm) 3.0 in (76 mm) 1.0 in (76 mm) ARC HEIGHT 0.0 mm) 3.0 mm) ALMEN STRIPS SHOT STREAM 4 to 6 in (102 to 152 mm) MEASURING DIAL 10--.32 SCREWS ALMEN TEST STRIP HARDENED BALL SUPPORTS 0. RESIDUAL STRESSES INDUCE ARCHING (b) STRIP MOUNTED FOR HEIGHT MEASUREMENT (c) Fig 5---6 Shot Peening Intensity Control 5.75 in (19.3.745 to 0.0. The peening time required to obtain 100 percent coverage should be recorded.031 + ---0. equipment requirements. Other areas optional. with masked area tolerances given.3.004 0.4 Coverage.3 Intensity.” 0 0 HRC 46 SHOT --.10 mm) wide.008 0. or N strip (see 5.014A per MIL---S---13165B.016 DEPTH IN INCHES Fig 5---7 Residual Stress by Peening 1045 Steel at 62 HRC with 330 Shot ANSI/AGMA 49 2004---B89 . but it can be specified to a closer tolerance for more repeatable results. At times.50 --. The range of arc height is generally 0. Mask area(s) indicated (if necessary).Gear Materials and Heat Treatment Manual should be specified to achieve higher magnitudes of compressive stress (refer to Fig 5---7).9.9. C. In some instances. A typical statement in a blueprint specification is “100 percent minimum coverage. Figure 5---8 illustrates the depth of the compressive layer on steel at 31 and 52 HRC hardness according to intensity.004 inch (0. 5.9. The intensity governs the depth of the compressive layer and must be specified as the arc height on the A.1). it is desirable to mask finished machined areas of the part from shot impingement. 100 percent coverage is adequate. 5. If masking is required. this should be stated in the shot peening requirements and defined on the drawing.9. 100 percent minimum coverage. 5.012 0.010---0.500 ---100 ---1000 ---150 HRC 61 SHOT ---200 ---1500 ---250 0 0. Typical masked areas would be finished bores or bearing surfaces. Use 55---62 HRC shot.6 Drawing Example. Shot peen area(s) indicated with S170 cast steel shot to an intensity of 0.3.3. it may be desirable to specify multiples of 100 percent in an attempt to achieve more blending of a poorly machined surface.5 Masking. In most cases.9.2. A typical example of drawing or blueprint specification for shot peening would be as follows: 5.3. 3.016 0.015 .7 2 1/2 --.0 . However. Variables such as gear geometry.030 . hardness.014 0.040 HRC 31 .010C 0 INTENSITY Fig 5---8 Depth of Compressive Stress Versus Almen Intensity for Steel Table 5---6 gives shot size and intensity for various diametral pitches. Diametral Pitch 8 --.010 .006 ----------- 0.25 . Additional comments for shot peening include the following: (1) All magnetic particle or dye penetrant inspections should be performed before shot peening.020 .2 3/4 --.002 . (5) When there are significant machining marks in the tooth roots.010A 0.9. honing. or polishing. 5.020A 0.50 . NOTE: The values for shot size and intensity should be considered typical and not mandatory.005 0 0 .008C (4) Compressive residual stress levels produced by shot peening can be quantitatively measured by X---ray diffraction.025 A . it is desirable to achieve an intensity sufficient to produce a depth of compressive stress to negate the stress riser effect of the machining mark.7 General Comments.008 .004 .010 0.025 .035 . It is possible to restore surface finish in peened areas (and retain beneficial effects) by lapping.16 4 --.75 .3 1/2 1 3/4 --.020 HRC 52 .005 0 . Currently this must be measured on a cut sample in a laboratory X---ray diffraction unit.015 .014A 0.1 Shot Size S110 S170 S230 S330 S550 (3) Generally all machining of areas to be peened are complete prior to shot peening. The plastic flow of the surface as a result of peening will tend to obscure minute cracks.006 0. shot diameter should not exceed 50 percent of the fillet radius. if material removal is limited to 10 percent of the depth of compressive layer. ANSI/AGMA 50 2004---B89 . Intensity 0.010 .Gear Materials and Heat Treatment Manual 1.018A 0.006 . and surface condition in the root may make other specifications more desirable. Table 5---6 Typical Shot Size and Intensity for Shot Peening (2) All heat treating operations must be performed prior to shot peening as high temperatures [over 450_F(232_C)] will thermally stress relieve the peening effects. Portable units are under development. honing or careful grinding of gears after final heat treatment maintains beneficial compressive residual stresses. skiving) will need to be individually evaluated as to effect on residual stress levels.1 Mechanically Induced Residual Stresses. The most common type of residual stress pattern in small diameter bars is a tensile stress at the surface and a compressive stress at the center. Quenching.10. Residual stresses (either favorable or unfavorable) are induced mechanically. In quenched carburized steels. Under extreme grinding conditions.10. In this situation. The phase transformation to martensite creates volume expansion producing tensile stress at the surface. induced. Residual stresses play an important role in the manufacture and performance of gears. There are two types of mechanically induced residual stresses.g. Finishing operations such as shot peening (refer to 5.2. 5. Residual stresses created by machining and heat treating operations are responsible for much of the distortion that occurs during manufacture. This in turn creates a compressive stress at the center. can also be considered a phase transformation stress.2. 5. machining stresses and finishing operation stresses. The following sections briefly discuss the causes of each type of induced residual stress. setting up residual tensile stress at the center and residual compressive stress at the surface. phase transformation and modification of surface chemistry stresses result from heat treatment of steel.2 Metallurgically Induced Residual Stress. 5. can affect the degree of in---process distortion and the residual stress state present in the finished parts. CBN grinding may also induce surface tempering residual tensile stresses. The residual stress distribution in finished gears can determine whether or not the gears will survive in service. For example.10 Residual Stress Effects. The other types of residual stress. This type of residual stress must also be considered in conjunction with thermal residual stress because modification of surface chemistry requires heating. Parts given a final heat treatment after finish machining may have the gross residual stresses from milling. This stress pattern results from the surface of a bar cooling faster than the center. generates both thermal and phase transformation stresses. the surface hardens but the center remains at an elevated temperature for some extended period of time.9) and roller burnishing also impart beneficial compressive residual stresses when properly controlled. turning.10. size of the bar and speed of the quench. Carburizing. however. and hobbing minimized by intermediate stress relief heat treatments in order to prevent significant distortion during the final heat treatment. 5. These operations are typically performed on finished gears to improve the pitting and surface bending fatigue resistance. the transformation temperature of austenite to martensite in the core occurs at a much higher Use of cubic boron nitride (CBN) grinding may have a favorable effect on the residual stresses in the finished gear. Other hard gear finishing methods (e. while the center will consist of residual compressive stress. Thermal stresses result from the heating and cooling of materials. and heating can introduce thermal stresses. particularly fast quenching to form martensite. one type of thermal stress. by phase transformation. or by modification of surface chemistry (such as by nitriding). Machining cuts taken just prior to final heat treatment must be light enough so as not to create significant residual stresses. When the sum of these two variables is large. will serve as a good example of these types of residual stresses.Gear Materials and Heat Treatment Manual 5. the most common type of surface chemistry modification. Quenching. Grinding after final heat treatment must be performed very carefully since it can create residual tensile stresses in the surface of the gear which can adversely affect performance. although quite different. the stress pattern will be of the second type with residual tensile stress at the center and residual compressive stress at the surface. These two types of stress patterns are determined by two variables. can all be categorized as being metallurgically ANSI/AGMA 51 2004---B89 .10. for example large diameter bar with a fast quench. which must be taken into account. the thermal contraction can not overcome the expansion from the martensitic formation and residual tensile stress will form at the surface.2 Residual Stresses by Modification of Surface Chemistry. When the cooling rates of the surface and center are similar.1 Thermal and Phase Transformation Stresses. thermally. The second and opposite type of residual stress pattern occurs during quenching of large diameter bars. Machining stresses are created by the cutting of the gear shape and can be either beneficial or detrimental. singularly and in combination (such as by carburizing). two types of residual stress patterns can form on quenching of a round bar. Lapping. Thermal. The thermal contraction exceeds the expansion of the transformation to martensite. Each of these. Material grade is certified by chemical test. and the other eight tests shall be on the drag side equally spaced around the gear. Recommended number of hardness tests are as follows: Outside Diameter. 90 degrees away from tests over the risers) and the other four tests shall also be on the drag side. Material hardness tests. eight tests shall be on the cope side (four over risers and four between risers around the gear). must be made with calibrated instruments with data substantiated and documented to insure reliability. two between risers also approximately 180 degrees apart. Large segmented gears shall be hardness inspected on the cope and drag rim edge of each segment per agreement between the customer and supplier. Metallurgical Quality Control Metallurgical information should be available regarding: (1) incoming material grade information (2) incoming material hardness and mechanical tests (3) heat treat process control (4) part characteristics (5) metallurgical testing (final product) (6) microstructure (7) test coupon considerations 6. When four hardness tests are specified.1 Cast Gears. 6. using any method or instrument. Hardness tests are made on the rim edge at mid rim thickness after final heat treatment. one shall be on the cope side.2 Incoming Material Hardness Tests. Spectrographic Analysis X---Ray Analysis Atomic Absorption Wet Chemistry When eight hardness tests are specified. NOTE: Source certification is commonly accepted for analysis certification. Iron casting grades are identified by their mechanical properties such as tensile strength. two tests shall be on the cope side. Therefore. four tests shall be on the cope side. the austenite to martensite transformation creates a volume expansion. Statistical process control (SPC) is an accepted method of control.2. preferably over a riser. transformation begins in the core and moves outward toward the case setting up tensile stresses in the core. and as discussed in the previous section.Gear Materials and Heat Treatment Manual temperature than the case. ASTM A370. 6. often specified in accordance with ANSI/AGMA 2 4 8 16 When two hardness tests are specified.40 (1020) Over 40 _ 80 (1020 to 2030) Over 80 _ 120 (2030 to 3050) (3050) Over 120 Refer to Appendix D on Service Life Considerations. are normally surface hardness tests made using: (1) Rockwell (2) Brinell (3) Rebound Tests (Equotip & Shore) Hardness testing. (two over risers approximately 180 degrees apart. Brass material grades are identified by chemical analysis. The expansion of the case is opposed by the previously transformed core imparting beneficial compressive stresses in the case. inches (mm) 0 --. They help counteract tensile stresses caused by bending in the root. Hardness may be specified but cannot be used to identify grade. yield strength.1 Incoming Material Quality Control. approximately 180_ away. (one over a riser and the other approximately 180 degree away between risers) and the other two tests shall be on the drag side 90 degrees away from the tests on the cope side. Minimum number of hardness tests on both rim or edge faces of through hardened cast and forged gear blanks is generally based on the outside diameter and increases with size. 90 degrees apart. Compressive stresses in the case help reduce surface pitting caused by tooth contact stress above and below the pitchline. the other on the drag side. and elongation. as the part is cooling. When sixteen hardness tests are specified. Bronze material grades are normally qualified using chemical analysis and hardness tests. Generally this is a destructive process. The following types of tests are commonly used and are listed in ascending order of cost for ferrous materials: (1) (2) (3) (4) Number of Tests Recommended (Rim Face) 52 2004---B89 . 6. Number of Tests Recommended 2 (180_ apart) 4 (180_ apart) 6. heating media. A291 and A148. base material composition. are only required when specified. Test bar stock. in the axial or longitudinal direction with respect to the component and the direction of metal flow during forging. (1) A minimum of four hardness tests shall be taken on the major (tooth) diameter of forgings up to fifteen inches. Recommended number of hardness tests is as follows: Diameter of Ring. 120 degrees apart. and also in ASTM A290. approximately 1. Three readings.2 Forged Pinions and Gears. are normally attached to the drag (bottom) rim edge of the casting or are cast as separate test blocks from the same heat of steel. (4) When a total of eight hardness tests are specified. Test bar stock should remain attached to or accompany the rough stock until all thermal treatment is completed. shall be taken at the mid radius on forgings of up to 18. for tensile testing and less frequently impact testing.4 Heat Treat Process Control. (2) When a total of four hardness tests are specified. they all shall be made 180 degrees apart on ANSI/AGMA 53 2004---B89 . Refer to 6. and any cosmetic change.2.Gear Materials and Heat Treatment Manual 6. One reading shall be taken approximately 1 inch (25 mm) from each end of the major diameter.0 inches (457 mm) in diameter.2. (1) A minimum of two hardness tests.2 Disc Shape Forging. types of controls. 180 degrees apart. Mechanical property test bars.3 Incoming Material Mechanical Tests.2. but are not primary factors for process control. they shall be 120 degrees apart on each rim edge. disc shapes and rings. Forged pinions and gears include cylindrical shapes. and part geometry.2. 180 degrees apart. shall be taken at the center of the length of the major diameter (center of tooth section at mid face). they shall be made 90 degrees apart on each rim edge. One reading shall be taken approximately 2 inches (50 mm) from each end of the major diameter. 90 degrees apart from one edge to the other. shall be taken at the center of the length of the major diameter (center of the tooth section at mid face). Two readings. rate of heating and cooling. such as distortion or part growth. cooling media. Test bar stock for gearing manufactured from forgings and bar stock are normally obtained from a prolongation or extension of the rough stock.2.1 Cylindrical Shaped Forgings. (3) When a total of six hardness tests are specified.0 inches (457 mm) in diameter. 6. evaluation techniques. condition of process equipment. inclusive. Process variables include: time. 6. Refer to ASTM A291 for mechanical test certification of forged gearing. two on each side 180 degrees apart. Process parameters used to control the heat treatment of gear materials are as follows: (1) When a total of two hardness tests are specified.8 for merits and limitations of mechanical test bars. 6. 180 degrees apart with one on each side. they shall be made 180 degrees apart.5 ¢ 5 ¢ 6. are characteristics of a specific heat treat process. 180 degrees apart. The many variables involved in the heat treatment of gear materials makes process control complex.3 Forged Rings (Reference ASTM A290). (2)A minimum of four hardness tests. such as coloration or surface texture.2. in (mm) Up to 40 (1016) Over 40 to 80 (1016 to 2032) Over 80 to 120 (2032 to 3048) Over 120 (3048) Minimum tensile properties for steel gearing are shown in Tables 4---2. Refer to ASTM A148 for mechanical test certification of cast gearing. shall be taken at the mid radius on forgings over 18. 6. one on the ring edge and the other on the opposite ring edge. Any dimensional change.0 inch (38 ¢ 127 ¢ 152 mm) long. 4---3 and 4---7. (2) A minimum of five hardness tests shall be taken on the major diameter of forgings over 15 inches (380 mm) in diameter. each ring edge. 6 (120_ apart) 8 (90_ apart) Heat treat processes change the microstructure and mechanical properties of the gear material. temperature. The concentrations of carbon dioxide and carbon monoxide in a furnace atmosphere at a given temperature are related to the carbon concentration on the surface of the part. the depth of carbon penetration during carburizing is dependent on how long the part was held at the carburizing temperature. There are three ANSI/AGMA 54 2004---B89 .4.3 Rate. It is easier and more cost effective to retemper a part that is too hard. commonly used methods for measuring and controlling carbon potential in a furnace atmosphere: (1) Water Vapor Concentration. 6. It is advisable to make a time temperature plot of the heat treat processes as a monitoring device and as process documentation. the rate of diffusion into steel is dependent on temperature.4. the core material will get too hot and lose its mechanical properties. than reharden and retemper a soft part. magnetic test. the proper operation of any device used for agitation. the uniformity of the temperature within the working dimensions of the furnace equipment should be measured. If a steel gear is cooled too quickly.5 Part Characteristics. the carbon concentration on the surface of the part is related to the water vapor concentration (dew point) in a furnace atmosphere. cleanliness and concentration (if applicable) of the quenchant. 6. Since the properties obtained in gear materials are dependent on the temperatures at which they are treated. The composition of the furnace atmosphere is an important part of process control. The duration of each segment of the heat treat process is critical to achieving the desired material properties. It is important that the tempering temperature be controlled to achieve the desired hardness.1 Temperature Uniformity.4. For example.5 Quench Control. The oxygen concentration is measured with an oxygen probe positioned in the furnace heat chamber. The concentration of carbon on the part surface is related to the oxygen concentration in the furnace atmosphere at a given temperature and carbon monoxide level.4. 6. The water vapor concentration is expressed as the atmosphere dew point measured in degrees fahrenheit. In carburizing and nitriding. (2) Carbon Dioxide Concentration. 6.4.4.Gear Materials and Heat Treatment Manual 6.2 Thermal History.4. and ensuring that the quenchant stays at the proper temperature (refer to 5. Control of carbon potential in the furnace atmosphere is critical to carburizing and the protection of surfaces from carbon pickup or depletion during the hardening process.2 Time. Specific temperature ranges are required to harden the various grades of steel. When the furnace temperature instrument indicates that the furnace chamber has recovered its heat. Temperature selection and control is an important parameter in the heat treatment of gear materials. The rates of heating and cooling are important considerations.75 hour per inch (25. 6.4 Atmosphere Control. the part in the chamber may not be up to temperature.7). Hardness and mechanical properties of a material grade are dependent on the tempering temperature after hardening.6 Tempering Temperatures.4 mm) of section. This includes inspecting the condition. Control of the quenching operation involves monitoring the variables which affect the rate and uniformity of part cooling. The carbon dioxide concentration is measured with an external infrared gas analyzer and expressed as a percentage. it will have high internal stresses and possibly crack. if an induction hardened part is heated too slowly.1. The amount of variation allowed is dependent on the type of heat treatment and the material properties desired. hot wire test and interval test. It is prudent to select an initial tempering temperature which is on the low side of the tempering range. Sample parts or test coupons can also be used as long as the test piece hardenability is accounted for (refer to 5. It is important that the part be held at temperature long enough for the entire part to be at temperature. 6. 6.1 Temperature.1. Time at temperature for through hardening is generally 0.7 on quenching). The water vapor concentration is measured using a dew cell or dew pointer. (3) Oxygen Concentration. This is usually accomplished with strip chart recorders. For example. For a given temperature. There are several methods available to monitor and quantify the cooling rate of the quenching process. 6.4. These include the standard nickel ball test. The carbon concentration in the furnace atmosphere is also temperature dependent. As quenched hardness of a part is a good indicator of the heat treat process.5.5.2.1. 6. or too low an austenitizing temperature. Tempering parts reduces hardness.Gear Materials and Heat Treatment Manual Part characteristics such as hardness. 6. 6. or a darker acicular pattern for marginal quenching. Statistical process control (SPC) is an accepted method to insure reliability using hardness testing. malfunctioning quench agitators. inadequate quenching. If the surface hardness is low. polished and etched. If the core hardness of a part is within the expected range regardless of the other hardness measurements.5. If the part hardness is greater in a heavy section compared to a light section. regrind surface until the hardness indentation is removed.2. 6.5. 6.1 Hardness. If a surface has been decarburized.1 Tempered Martensite.2 Microstructure. However. the microstructure will be composed primarily of tempered martensite provided that the hardenability of the steel was adequate.1 As Quenched Hardness.5. Retained austenite can be transformed to martensite by freezing the carburized part.2 Bainite. ANSI/AGMA 6. If a carburized part has an excessively high carbon concentration. If a hardened gear has been correctly hardened and tempered. As tempering temperature increases. mainly type of steel and as quenched hardness. it may be due to the presence of retained austenite in the carburized case.1. Low as quenched hardness usually results from one or more of many factors such as deteriorating quenchant. 6. the part was satisfactorily quenched. but each type has its own application limits and must be used correctly.4 Carburize and Harden Examination.5.5. 6. if the carbon content of the carburized case is high. If the hardness increases. Retained austenite is characterized by a white background in a matrix of other structures (see 6. A hardness measurement technique can be used to monitor furnace soak time and uniformity.1.5. it is advisable that two hardness checks be made on a qualifying test part to insure that the hardness below the decarburized zone meets blue print requirements. this is a good indication of a processing problem. It should be noted. 6.5. The composition of the various phases in the microstructure of a gear will tell a lot about the heat treat process. a test coupon or part that was run with the load should be sectioned. If the part hardness varies from the specified range between pieces in a furnace load.2 Decarburization. excessive retained austenite.5.1. there is no decarburization. If the surface hardness of a carburized part is low. To determine the depth of decarburization. hardness will be low. however. a larger percentage of retained austenite will be present and will reduce the case hardness. there was retained austenite in the carburized case which is an indicator of high surface carbon concentration or too high of a quench temperature. micro--structure and test coupon results can provide valuable information.6 Retained Austenite Examination.1. Tempering temperature is determined by many factors. undissolved carbides. There are numerous types of hardness testing devices which can be used.2. High as quenched hardness is the result of good heat treatment. 6.1.3 Retained Austenite.5. If a gear has been improperly quenched. Many factors determine the as quenched hardness such as decarburization and retained austenite. 55 2004---B89 .1. It is recommended that a trained metallographer or metallurgist perform the microstructure analysis. or low surface carbon. this is an indication of decarburization. too high tempering temperature. or if the hardness increases as surface metal is removed. Hardness is the most common characteristic used to measure results of the heat treat process.2. The two hardness checks should be made using the following sequence: grind surface for hardness measurement. Carburized case depth is typically measured by making a microhardness traverse across a sectioned part or test coupon to find the depth from the surface where the hardness is equivalent to Rockwell C 50. the microstructure might be interspersed with bainite.6). mounted.4 Undissolved Carbides. these are good indicators of insufficient soak time. All carburized case microstructures will contain some retained austenite.5. Surface hardness and core hardness measurements are used to monitor the carburizing process.5 Case Depth Examination. hardness decreases. there is possible decarburization. 6. 6. If the part hardness is low.5. and then make another hardness measurement near the original location. that in most cases decarburization is not permissible. If both measurements are the same. inadequate case depth.3 Post Temper Hardness Examination. usually less than 5 to 30 percent by volume. If the surface hardness improves after freezing. which is characterized by a feathery appearance if severely under quenched. Other portable hardness testing instruments are available (ASTM A833). It is desired that surface hardened gearing be hardness inspected. Conventional Rockwell test machines can be used to hardness inspect surface hardened gearing when size of the gearing permits and where a visible impression is permitted. so as not to leave an objectionable impression.3 Test Coupons. Miner’s Rule is a widely accepted method of making these comparisons. In low cycle fatigue where most high overload and damage fractures occur. Since the distribution may be considered a log function. 6. Hardened files. Comparison is made of the ball diameter on each to determine hardness of the unknown. Damage can be compared with that for the product design conditions. 6. surface temper inspection. One tester uses a hammer to simultaneously impact a known hardness test bar and the unknown workpiece with a hardened ball between the two test surfaces. generally 64 microinches (5 microns). including those tempered to lower hardness than 60---64 HRC. This can be done by running the test at some overload ratio and evaluating the damage with time for the test conditions. destructive sectioning and testing may be required. table Brinell and Rockwell test machines provided that the following are met: (1) Surface to be inspected provides access and has the required surface finish. or: (2) If the size of the hardness impression on the test surface is permitted. or: (3) Mass of the test surface will support the test load. 6. top lands of teeth where size permits. This comparison must be made for both the beam strength and the surface durability of the teeth. may be used. A normal structure will consist of light. Through hardened gearing is rarely inspected for hardness on the flanks of teeth or in root radii because hardenability of the steel selected should insure obtaining the specified hardness at these locations. gap of herringbone (double helical) gearing and on adjacent diameters of pinions other than bearing journals. while a structure of excessively high carbon concentration will have carbides contained in a network at the grain boundary. This would constitute a Miner’s Rule damage of ten. Fatigue (life) testing of the final product is the proof of the suitability of the design for the intended purpose. Microstructure and hardness testing of test coupons can be correlated to gearing characteristics. Hardness measurement in the roots of teeth may not When damage value accumulated on the test equals the damage value of the design. can also be used to approximate hardness by the scratch test (Reference SAE J---864). Through hardened gearing is commonly inspected on the faces of gear rims.6. Other portable instruments measure the recoil or rebound height or velocity of a dropped hardened ball. It is desirable to expedite this testing while maintaining validity of the test data. or use a high ultrasonic frequency activated indenter to measure hardness. the test specimen survived the minimum specified product life. 6. magnetic particle inspection.5.6 Metallurgical. Portable testers which measure the rebound height or velocity of a dropped hardened ball or use a high ultrasonic frequency activated hardness indenter. scattered pinpoint carbides.2 Hardness Testing on the Gear Product.6. Due to the statistical nature of fatigue failure there is a wide distribution of data. When hardness testers are not available for accurate measurement at roots of teeth. it is necessary for about half the test units to run at ten times the threshold life to validate the product design. this scatter band from the lower threshold to the upper threshold is approximately 100 to 1 wide. Mechanical and Non--. Inspection of the hardness on the flanks of surface hardened coarse gearing with non---destructive portable hardness testers can be improved when the instrument can be fixed for perpendicularity to the test surface. Through hardened finish machine gearing can be conventionally hardness tested by standard and porANSI/AGMA 56 2004---B89 . Tests and inspections which may be made on the final or near final product are fatigue testing. non---destructively. and ultrasonic inspection. Test coupons of representative geometry are frequently used for destructive testing in lieu of destroying gearing. hardness testing.Destructive Tests and Inspections. Continuous intergranular carbide network is not desirable for gearing.Gear Materials and Heat Treatment Manual the microstructure will contain undissolved carbides usually populating the case.1 Fatigue Testing. Undissolved carbides are characterized by blocky white regions in a matrix of martensite and retained austenite. Gear Materials and Heat Treatment Manual be reliable due to accessibility in the radius of curvature and surface roughness. For improved accuracy and where permitted, through hardened steel and cast iron gearing should be hardness inspected directly in Brinell (not converted). Hardness of surface hardened gearing should be directly measured in Rockwell (C or A scale) or converted to Rockwell with suitable portable instruments. be used in some instances. Caution should be exercised if the heavier load C scale is used. 6.6.4 Magnetic Particle Inspection. Magnetic particle inspection is a non---destructive testing method for locating surface and near surface discontinuities in ferromagnetic material. When a magnetic field is introduced into the part, discontinuities laying approximately transverse to the magnetic field will cause a leakage field. Finely divided ferromagnetic particles, dry or in an oil base or water base suspension, are applied over the surface of the material under test. These particles will gather and hold at the leakage field making the discontinuities visible to the naked eye. Portable instruments vary in accuracy and reliability. Users, therefore, should take precautions to insure accurate calibration and test results. Hardness testing equipment manufacturers should be contacted and literature searched for additional information on principles of hardness inspection, available test equipment and their capabilities. Statistical process control is a useful tool to be used with hardness testing. Use of electric current is, by far, the best means for magnetizing parts for magnetic particle inspection. Either longitudinal or circular fields may be introduced into parts. There are basically two types of electric current in common use, and both are suitable for magnetizing purposes in magnetic particle testing. The two types of current are direct current and alternating current. The magnetic fields produced by direct and by alternating currents differ in many characteristics. The main difference, which is of prime importance in magnetic particle testing, is that fields produced by direct current generally penetrate the entire cross section of the part, whereas the fields produced by alternating current are confined to the metal at or near the surface of the part under test. From this, it is evident that when deep penetration of field into the part is required, direct current must be used as the source of magnetizing force. By far, the most satisfactory source of D.C. is the rectification of alternating current. Both single phase and three phase A.C. are furnished commercially. By the use of rectifiers, reversing A.C. is rectified and the delivered direct current is entirely the equivalent of straight D.C. for magnetic particle testing purposes. 6.6.3 Surface Temper Inspection. Surface temper inspection is used to detect and classify localized overheating on ground surfaces by use of a chemical etch method. Details of the process are covered in AGMA 230.01, Surface Temper Inspection Process. Inspection criteria includes a class designation for critical and non---critical areas. To evaluate the severity of surface temper, grinding burns are classified by intensity of color from light gray to brown to black. Severe burning or re---hardening is indicated by patches of white in the darkened areas. Cracking may also be present. Re---hardening or cracking are cause for rejection. Tables I and II in AGMA 230.01 cover temper classes ranging from Class A (Light temper) to Class D (Heavy temper). Class C (Moderate temper) for a limited area and hardness reduction may be permitted. Rework for excessive temper is generally permitted by mutual agreement between customer and supplier. Sources of alternating current are single phase stepped down to 115, 230, or 460 volts. This is accomplished by means of transformers to the low voltages required. At these low voltages, magnetizing currents up to several thousand amperes are often used. The trend in Europe is to use A.C. current for magnetic particle testing because the intent of their testing is location of surface discontinuities only. Subsurface discontinuities are best detected by radiography or ultrasonic non---destructive test methods. A.C. currents tends to give better particle mobility, and Case depth shall be determined on a normal tooth section. Hardness testers which produce small shallow impressions should be used in order that the hardness values obtained will be representative of the surface area being tested. Microhardness testers which produce Diamond Pyramid or Knoop Hardness number are recommended, although other testers such as Rockwell superficial A or 15 N scales can ANSI/AGMA 57 2004---B89 Gear Materials and Heat Treatment Manual demagnetization is more complete than with a D.C. field. (7) For prod magnetization with direct current, a minimum of 60 amperes per inch of prod spacing will produce a minimum magnetizing force of 20 oersteds at the midpoint of the prod line for plate 3/4 inch thick or less. A safer figure to use, however, is 200 amps per inch, unless this current strength produces an interfering surface power pattern. Prod spacing for practical inspection purposes is limited to about eight (8) inches maximum, except in special cases. There are two essential components of magnetic particle testing, each of equal importance for reliable results. The first is the proper magnetization of the part to be tested, with proper field strength in the appropriate direction for the detection of defects. The second is the use of the proper magnetic particles type to secure the best possible defect indications under prevailing conditions. 6.6.4.1 General Principles. Some general principles and rules on magnetizing means, field strength, current distribution and strength requirements are listed below (refer to Figs 6---1 and 6---2). (8) All parts should be demagnetized after magnetic particle inspection. FIELD (1) Fields should be at 90 degrees to the direction of defects. This may require magnetizing in two directions. HEAD BATH (2) Fields generated by electric currents are at 90 degrees to the direction of current flow. (3) When magnetizing with electric currents, pass the current in a direction parallel to the direction of expected discontinuities. CURRENT DISCONTINUITY (4) Circular magnetization has the advantage over longitudinal magnetization in that there are few, if any, local poles to cause confusion in particle patterns, and it is preferred when a choice of methods is permissible. HEAD SHOT CIRCULAR MAGNETIZATION LOCATES DISCONTINUITIES OCCURRING 45 --- 90 DEGREES TO THE DIRECTION OF THE FIELD. (5) Circular magnetization specifications generally require from 100 to 1000 amps per inch of part diameter. Amperage requirements should be incorporated into the magnetic particle procedure. INSPECT FOR PARTICLE INDICATIONS SHOWING LONGITUDINAL DISCONTINUITIES --- MARK DISCONTINUTIES. Fig 6---1 Circular (Head Shot) Magnetic Particle Inspection (6) For coil magnetization, a widely used formula for amperage calculations is: NI = 45 000 L/ D 6.6.4.2 Magnetic Particles. The particles used are finely divided ferromagnetic material. Properties vary over a wide range for different applications including magnetic properties, size, shape, density, mobility and visibility or contrast. Varying requirements for varying conditions of test and varying properties of suitable materials have led to the development of a large number of different types of available materials. The choice of which one to use is an important one, since the appearance of the particle (Eq 6.1) where NI = ampere turns required, L/D = length to diameter ratio. NOTE: The 45 000 constant may vary with specifications. ANSI/AGMA 58 2004---B89 Gear Materials and Heat Treatment Manual patterns at discontinuities will be affected, even to the point of whether or not a pattern is formed. FIELD methods is in the range of 60 to 40 microns. Particles larger than this tend to settle out of suspension rapidly. In general, wet method materials exhibit a greater sensitivity than dry powders. Fluorescent particles have the greatest contrast of the wet method materials. Although fluorescent wet particles have the greatest sensitivity and contrast, they can provide a confusing background on surfaces with a finish greater than 250 RMS. CURRENT THROUGH COIL BATH 6.6.4.3 Documented Procedures. Written procedures for magnetic particle testing should as a minimum include: (1) Which ASTM, ASNT or agency specifications the procedure meets. (2) Qualifications--(a) Indicate that the operators are qualified and tested to ASNT---TC---1A Level II, MIL--STD---271F, etc. (b) Indicate type of equipment used for inspection, A.C. and D.C. full wave rectified, etc. (c) Indicate type of particles used for inspection, fluorescent or black visible, wet or dry particle. For the wet method, particle concentration should also be indicated. (3) General--(a) State when inspection is to be done; after heat treat, finish machining, etc. (b) State what the surface will be; for example, 250 RMS, black forge, etc. DISCONTINUITY COIL SHOT LONGITUDINAL MAGNETIZATION LOCATES TRAVERSE DISCONTINUITIES. INSPECT FOR PARTICLE INDICATIONS SHOWING TRANSVERSE DISCONTINUITIES. NOTE: EFFECTIVE LENGTH MAGNETIZED BY COIL SHOT IS A FEW INCHES ON EITHER SIDE OF COIL. MAXIMUM LENGTH OF ARTICLE COVERED BY ONE SHOT IS 18 INCHES (46 CM). ON LONG ARTICLES, REPEAT SHOTS AND BATHS DOWN THE LENGTH OF ARTICLE. PLACE ARTICLES CLOSE TO THE COIL BODY. Fig 6---2 Coil Shot Magnetic Particle Inspection (1) Dry Powders. It is evident that size plays an important part in the behavior of magnetic particles. A large, heavy particle is not likely to be arrested and held by a weak field when such particles are moving over the surface of the part. On the other hand, very fine powders will be held by very weak fields, since their mass is very small. Extremely fine particles may also adhere to the surface where there are no discontinuities, especially if it is rough, and form confusing backgrounds. Most dry ferromagnetic powders used for detecting discontinuities are careful mixtures of particles of all sizes. The smaller ones add sensitivity and mobility, while the larger ones not only aid in locating large defects, but by a sweeping action, counteract the tendency of fine powders to leave a dusty background. Thus, by including the entire size range, a balanced powder with sensitivity over most of the range of sizes of discontinuities is produced. (c) State amps per inch of diameter for circular magnetization and the formula used for calculation of longitudinal magnetization. (d) State what method will be used for determining field magitude; such as pie gage, etc. (e) State demagnetization, if required, and level of demagnetization required. (4) Standard of Acceptance (a) Indicate maximum size and density of indications permitted. (b)Indicate reporting procedures if needed. For further information on magnetic particle testing, refer to: Principles of Magnetic Particle Testing, C.E. Betz Metals Handbook Volume II Eighth Edition Nondestructive Inspection and Quality Control Nondestructive Testing Handbook, Edited by Robert C. McMasters for the Society for Nondestructive Testing (2) Wet Method Materials. When the ferromagnetic particles are applied as a suspension in some liquid medium, much finer particles can be used. The upper limit of particle size in most commercial wet ANSI/AGMA 59 2004---B89 The microstructure will vary around the gear tooth flank and throughout the tooth cross section. As an example. Ultrasonic Examination Thereof. test specifications and interpretation of test results. Scanning sensitivity and indication limitations are often determined using test blocks by establishing a distance---amplitude reference line on the oscilloscope screen as illustrated in Fig 6---4. the transducer both emits sound waves and receives the returning signals from the back surface and possible defects. The indication to the left of the oscilloscope screen in Fig 6---3 is caused by the sound wave entering the steel and is called “initial pulse” or “contact interference. Ultrasonic Examination of Heavy Steel Forgings. glycerin or a commercial paste spread evenly on the surfaces to be inspected. Hardened steel gearing microstructure should be tempered martensite at the entire tooth surface. (2) ASTM A609. Section 11. depending upon the media. Carbon and Low Alloy. Depth of the defect from the transducer contact point on the scanning surface can.” The indication to the right is caused by sound reflecting off of the back surface and in the middle is the signal reflecting from any defects shown. such as the outside diameter and ends or end faces of cylindrical or disc shaped rough stock are generally machined to 125---250 micro---inch maximum surface roughness. for additional information. One method uses a couplant: oil. A straight line is drawn between the two points. called the “sweep line. The heat treatment variables will Before testing. as related to the rate of travel of sound in the material. both expressed in a percent of the back reflection height established during calibration for scanning sensitivity. Reference can be made to the equipment manufacturer’s literature.Gear Materials and Heat Treatment Manual 6. the indication from the same size FBH in the 12 inch (305 mm) block is noted on the oscilloscope screen. The tooth mass will have a significant effect on the resulting microstructure and hardness throughout the tooth section. Steel Castings. or at the sensitivity to obtain an indication of specified height from a flat bottom hole drilled into test blocks. Surfaces to be scanned. Untreated coarse grained structures do not lend themselves to ultrasonic testing. (2) ASTM A388.7 Microstructure. indications are often specified not to exceed a certain magnitude and length on the scanning surface or result in loss in back reflection height exceeding specified limits. Very short sound waves of a frequency greater than 20. the pulse echo technique. The major function of the material selection and heat treating process is to achieve the desired microstructure at the critical locations so that the part will have the desired contact and bending strength capacity. ANSI/AGMA 60 2004---B89 . Volume 11 on “Non---Destructive Testing” (SNDT). There are two test methods used. The sweep line can be calibrated by use of a test block or section of known thickness in the work piece in order that each marker shown on the sweep line represents a standard distance or depth. operator requirements and qualification. returning sound waves are transformed into voltage and monitored on an oscilloscope screen. be determined.” provides a measure of distance or depth in the work piece. Any indication noted must not exceed the determined distance---amplitude reference line. test block requirements. Also. sensitivity may be adjusted to establish the specified indication height [2 1/2 inch (63 mm)] from the flat bottom hole (FBH) in the 4 inch (102 mm) block. application limitations.5 Ultrasonic Inspection. In the method most often used. The horizontal line. The American Society for Testing Materials and AGMA specifications which follow may be used for ultrasonic inspection of wrought and cast gearing. Ultrasonic inspection is a nondestructive test method to determine the internal soundness and cleanliness of gearing by passing sound (ultrasound) through the material. Important considerations include appropriate transducer frequency. Scanning sensitivity is often established as either the sensitivity to just obtain a specified back reflection height. The second method uses water as the couplant. and at the same sensitivity. or to the American Society for Metals (ASM) Metals Handbook. Castings: (1) AGMA 6033---A88. This provides improved contact for the transducer with the work piece. for coupling the ultrasonic transducer to the heat treated work piece.000 cycles per second (audible limit) are voltage generated and transmitted into the part by a transducer. Section 10. instrument calibration. Forgings and bar stock: (1) AGMA 6033---A88. therefore. With the most common technique of ultrasonic inspection. the instrument must be calibrated according to the test specification.6. namely. with the transducer and work piece submerged in a tank. work piece requirements (grain size). 6. The returning signals are subsequently monitored on an oscilloscope screen as shown in Fig 6---3. Gear tooth quality control must include microstruc- ture considerations as well as hardness control. TRANSDUCER SUITABLE COUPLANT ON SURFACE X Y DEFECT BACK REFLECTING SURFACE INITIAL PULSE BACK REFLECTION Y 3 in (76 mm) X DEFECT MARKERS Fig 6---3 Ultrasonic Inspection with Oscilloscope Screen ANSI/AGMA 61 2004---B89 .Gear Materials and Heat Treatment Manual significantly effect the microstructure achieved. 62 2004---B89 . Discontinuous carbide network is generally allowed within limits. pearlite. Data and opinions vary as to the allowable limits for retained austenite. Subzero treatment is specified for some applications to reduce retained ANSI/AGMA Bainite. Continuous network carbide is generally considered to be unacceptable microstructure. carbide forms and distribution are an area of microstructure concern. retained austenite will exist in the case after the heat treating operations.Amplitude Reference Line for Ultrasonic Inspection austenite. Control of the microstructures in flame and induction hardened steel gears must also consider the width and location of heat effected zones which will always exist at the ends of the hardened pattern. In carburized and hardened steel gears. Microstructure evaluation must include the existence of structures other than tempered martensite at the gear tooth surface and at core positions. Some research has shown that microcracks are produced by subzero treating. In carburized and hardened steel gears. These structures will exist in core microstructures of coarse tooth gearing. and ferrite are undesirable at the gear tooth surface of surface hardened gearing.Gear Materials and Heat Treatment Manual INDICATION FROM FBH IN 4 in (102 mm) BLOCK INDICATION D ---A REFERENCE LINE FROM FBH IN 12 in (306 2 1/2” mm) BLOCK (63 mm) 3 in (76 mm) 11 in (279 mm) TEST BLOCKS: 12 AND 4 in (306 AND 102 mm) TEST BLOCKS CONTAINING SAME SIZE FLAT BOTTOM HOLE DRILLED TO A DEPTH OF 1 in Fig 6---4 Distance --. and its effect related to improved solidification mechanism (reduced micro---segregation and micro---unsoundness) and increased response to heat treating. provides optimum properties compared to properties from the transverse (or tangential) direction. however. Generally.g. provided hardness of the test coupons is within the specified range. Test coupon may be better located during heat treatment. In addition to test coupons providing indications as to the metallurgical quality of gear materials.9) which means that properties vary in the longitudinal and transverse (or tangential) directions. This variance is due mainly to the increased degree of mechanical working and increased response to heat treating. especially tensile ductility (percent elongation and reduction of area measured after tensile testing). better represent actual corresponding properties of gearing. Tensile and yield strengths of test coupons. 6. The transverse (or tangential) direction is more representative of gear teeth depending upon helix angle. (2) Castings--(a) Mass effect. however. Location or depth of the test coupon from the forged section (e. smaller section test bars and sections show improved mechanical properties. test results from shaft extensions in the longitudinal direction are those typically reported by forging manufacturers for solid on shaft gearing. These directions are defined with respect to direction of metal flow and inclusion orientation induced by mechanical working. are generally higher for test coupons than for actual forged or cast gearing.2.2 Mechanical Properties Affected.Gear Materials and Heat Treatment Manual (e. NOTE: It should be realized. causes variance in mechanical properties. 6. Smaller section test coupons are typically specified for economic considerations and instrument testing limitations. Segregation is increased and degree of mechanical working is reduced towards the center of hot worked or wrought sections.8. Also. Mechanical properties obtained from test coupons. causing increased response to heat treating and improved mechanical properties.g. Test coupons are specified by company and industry standards for evaluating mechanical properties of wrought and cast steel and non---ferrous materials used for gearing. Small section of the test bar being tested. The reasons for mechanical properties obtained from test coupons not being equivalent to those of gearing include the following considerations: (1) Wrought Forgings and Bar stock--(a) Test coupon orientation and location. cast iron and non---ferrous alloys are not equivalent to the actual properties of gearing from which the test coupons were obtained or associated. that mechanical properties obtained from test coupons for wrought and cast steel. (b) Location of the test coupon. not typical properties. 6. Unless otherwise specified.8. the smaller section of the standard integral or separate cast test coupons. causes mechanical property variance compared to larger cast sections. Specified mechanical properties for test coupons should be minimum properties. has an effect on mechanical properties. impact strength and fatigue strength.1 Reasons for Mechanical Property Variance. such as standard impact test bars. 6.1 and 6.8. mid--section or from the center) and its effect with respect to the degree of mechanical working and segregation. Mechanical properties obtained from test coupons should be considered as an indication of the quality of gear materials. Mechanical properties of forgings and bar stock are anisotropic (refer to 4. but should not be interpreted as representing the precise mechanical properties of gearing for the reasons cited in 6. and the smaller section of the gearing from which the test coupon may have been obtained ANSI/AGMA 63 2004---B89 . (b) Mass effect. The longitudinal direction. as compared to larger forged sections. from the outside diameter. shaft extension). Designers should incorporate appropriate factors of safety based on experience for design of gearing to accommodate variance between measured and actual properties of gearing.3 Interpretation. test coupons provide a comparison of steel quality between different orders and can often help identify problems in steel making and heat treating. however.8 Mechanical Property Test Bar Considerations.8.8. results in improved properties compared to larger cast sections. Small section of the test bar being tested. Process for Heat Treatment of Steel Reference Addresses American Society for Metals Metals Park. 20036 (202) 452---7100 AISI Steel Products Manuals Naval Publications and Forms Center 5801 Tabor Avenue Philadelphia. PA 19103 (215) 299---5400 ASTM Standards Metal Powder Industries Federation 105 College Road East\Princeton. D. Reference Photographs for Magnetic Particle Indications on Ferrous Castings ASTM E186---80. PA 19120 (215) 697---3321 Military Standards American Society for Testing and Materials 1916 Race Street Philadelphia. Heavy---Walled. for Steam Turbines ASTM E125---63 (1980). NJ 080540 (609) 542---7700 MPIF Standard 35 Society of Automotive Engineers. OH 44073 (216) 338---5151 Metals Handbooks Heat Treaters Guide Metals Reference Book American Iron and Steel Institute 1000 16th Street. 400 Commonwealth Drive Warrendale. Standard Reference Radiographs for Steel Castings Up to 2 inch (51 mm) in Thickness ASTM E609---83. Inc.C. Carbon and Low Alloy. Standard Reference Radiographs for Heavy Walled (4 1/2 to 12 inch)(114 to 305 mm) Steel Castings ASTM E446---81. Ultrasonic Examination of Carbon and Low Alloy Steel Castings ASTM E709---80.Gear Materials and Heat Treatment Manual Bibliography ASTM A148---83. Magnetic Particle Examination MIL---H---6875G (Feb 86). NW Washington. Specification for Carbon and Alloy Steel Forgings for Pinions and Gears for Reduction Gears ASTM A356---83. Specifications for Steel Castings for High Strength Structural Purposes ASTM A291---82. Specification for Steel Castings. PA 15096 (412) 776---4841 SAE Handbook AMS Standards ANSI/AGMA Other: Gray and Ductile Iron Castings Handbook Cast Steel Handbook Modern Plastics Encyclopedia 64 2004---B89 . Standard Reference Radiographs for Heavy Walled (2 to 4 1/2 inch)(51 to 114 mm) Steel Castings ASTM E280---81. plastic gearing materials are noted for low coefficient of friction. Both thermosetting and ther- ANSI/AGMA 65 2004---B89 . SAN is a stable. and are finding their way into more markets as a molded gearing material in competition with nylon and acetal. A2. Operating Characteristics. and quiet operation. Very little degradation of mechanical properties in certain thermosetting materials occurs at temperatures up to 450_F(232_C). with glass and minerals with and without lubricants. therefore. A5. however.5 Polycarbonate (T/P). The purpose of this Appendix is to provide information on plastic materials which have been used for gearing. Load Carrying Capacity. A5. Nylon is a family of thermoplastic polymers. such as PTFE and MoS2. but nylon 6 and nylon 12 are also used. Some nylons absorb moisture which may cause dimensional instability. when operating at low stress levels in certain environments. the tolerances for plastic gears may be less critical than for metal gears for smooth and quiet performance. glass. Plastic Materials. therefore. A5. sisal. low shrinkage material for producing consistently accurate molded gears. Acetal has a lower water absorption rate than nylon and. Tolerances. Polyimide is usually 40---65 percent fiber glass reinforced and has good strength retention when used at high operating temperatures.indicates thermosetting). is more stable after molding or machining. A5. Many different plastics are now used for gearing. mineral. Nylon may be compounded with various types and amounts of glass reinforcing materials. as well as one version with fibrous PTFE. refer to appropriate product standards. chopped cloth. Phenolics are invariably compounded with various fillers such as woodflour. Polyesters are both unfilled and with glass fiber. The upper temperature limit of most thermoplastic gears is 250_F(121_C) at which point they lose approximately 50 percent of their rated strength. Many plastic gearing materials have inherent lubricity so that gears require little or no external lubrication.6 Polyester (T/P). A5.indicates thermoplastic). Polyurethane is generally noted for its flexibility and. and such lubricants as PTFE (polytetrafluorethylene) and graphite. and such lubricants as PTFE and MoS2 (molybdenum disulfide).7 Polyurethane (T/P). The most widely used of any molded gearing material is nylon 6/6. the same care in manufacturing. A4. Phenolics are generally used in applications requiring stability. Purpose. measuring. The upper operating temperature limit of thermosetting gears now exceeds 400_F(250_C). A5. The inherent resiliency of some of the plastic used may result in better conjugate action. The maximum load carrying capacity of most plastic gears decreases as the temperature increases more than with metal gears.1 Phenolic(T/S --. Generally. has the ability to absorb shock and deaden sound. A5. The resiliency of many plastic gears gives them the ability to better dampen moderate shock or impact type loads within the capabilities of the particular plastics materials. Acetal polymers are used unfilled or filled. A5.2 Polyimide (T/S). low shrinkage material and is used in some lightly loaded gear applications. testing. and when higher temperatures are encountered.3 Nylon(T/P --. Gear Materials and Heat Treatment Manual. A3. with the latter being by far the most prevalent.Gear Materials and Heat Treatment Manual Appendix A Plastic Gear Materials [This Appendix is provided for informational purposes only and should not be construed as part of AGMA Standard 2004---B89. mineral fillers. high efficiency performance. Polycarbonate is generally used with the addition of glass fiber and/or PTFE lubricant and is a fine. have been known to outwear equivalent metal gears. A5. For physical properties. Under certain operating conditions.4 Acetal (T/P). Plastic gearing. and quality level specifications should be utilized in plastic gearing as in metal gearing.] A1. moplastic material are used.8 SAN (Styreneacrylonitrile) (T/P). They can perform satisfactorily when exposed to many chemicals which have a corrosive effect on metal gears. Ordinarily. and thus may require a hardened steel mate and adequate lubrication.1 Inspection. and rectangles of various sizes from which gears can be machined. squares.3 Burrs. The quality of machined gears may be generally better than their molded counterparts. Lower density than metals often provides higher strength to weight ratios. if not eliminated by back up discs or subsequent removal by other means. Laminated Phenolics Plastics. Several plastic gears can be molded together as a gear cluster. A6. notably unfilled nylon and acetal. Many of these plastic materials.Molded. and creep. The glass fabric base grades have good heat resistance and very high tensile and impact strength.Gear Materials and Heat Treatment Manual A8. Chopped fabric impregnated with phenolic resin is capable of being molded as a gear but may require finish machining to meet most commercial quality requirements. than an equivalent machined gear. Plastic Gearing References. or mat. because of the flow of the material into the tooth cavity of the mold. A8. Gear Blanks. Machined and Other Methods. paper. Gears can be molded at less cost if large quantity warrants the cost of the mold. The following considerations will assist in obtaining higher quality machined parts. glass fabric. even at elevated temperatures. These materials are impregnated or coated with a phenolic resin and consolidated under high pressures and temperatures into various grades which have properties useful for gearing. Plastics Gearing --. ANSI/AGMA 66 2004---B89 . such as rounds. It should be noted that all grades have some dimensional change due to humidity. AGMA 141. A8. Fabric base grades are tougher and less brittle than paper base grades. Polymer elastomer is a newcomer to the gearing field. and high wear resistance. Feather edge burrs. Gears of linen base phenolic are abrasive. Final tooth strength is generally better in a molded gear. Sharp cutting tools are necessary to avoid tooth profile and size variation due to deflection. When compounded with 40 percent glass fiber with or without internal lubricants. Asbestos---phenolic grades have excellent thermal and dimensional stability. Combinations of gears. sprockets.9 Polyphenylene Sulfid (T/P). The modulus of elasticity is so low in plastics that errors in measurements are very difficult to control. A9. A10. Phenolics are used for fine pitch gears due to economy. pulleys. The linen grades made with finer textured lightweight fabrics will machine with less trouble. A5. asbestos. Part Combinations. whether in sheet or rod form. but the molded tooth surface is superior to the machined surface in smoothness and toughness.3 Chopped Fabric Molding Compound. A9. cotton fabric. These products.2 Performance Characteristics. A9. are available in standard extruded shapes. The use of controlled load checking equipment is almost mandatory to avoid errors in measurements. and to resist wear. than most materials previously available. Fabric base grades are chosen to withstand severe shock loads and repeated bending stresses. high resiliency.01. among other advantageous characteristics. Machined Plastics Gears. A5. and cams can also be produced as a single part. impact. A8. and has excellent sound deadening qualities and resistance to flex fatigue. Gear cutting is done on standard machines and with standard tools. it has been found in certain gear applications to have much greater strength. A9. will impair inspection of gearing and possibly contribute to noise during operation.2 Tools. A7.1 Industrial Laminated Thermosetting Products.10 Polymer Elastomer (T/P). contain laminations or plies of fibrous sheet materials such as cellulose. Illustrations. NOTES: * Maximum controlling section sizes higher than those above can be recommended when substantiated by test data (heat treat practice). and recommended maximum controlling section sizes for several low alloy steels from AGMA 6033---A88. dependent upon specified core hardness. illustrations as to how maximum controlling section size is determined for gearing. Other special stock allowances such as those used to minimize distortion during heat treatment must be considered. Marine Propulsion Gear Units. ** Higher specified hardnesses (e. Gear Materials and Heat Treatment Manual. Also presented are factors which affect maximum controlling size. NOTE: Evaluation of the controlling section size for the selection of an appropriate type of steel and/or specified hardness need not include consideration of standard rough stock machining allowances. 388---321 HB and 401---444 HB) are used for special gearing.0 (76) included Not recommended Not recommended Not recommended No restriction ] No restriction No restriction To 25.5(140) included To 4. Part 1. 375---415 HB. Figure B---1 illustrates controlling sections for quenched gear configurations whose teeth are machined after heat treatment. Reference should be made to 4. The maximum controlling section size for steel is based princi- pally on hardenability. Maximum recommended controlling section sizes for nitrided gearing are less than those above for the same hardness range because of higher tempering temperature required for nitriding gearing (refer to 5. Materials. depth of desired hardness. Definition. Table B---1 Approximate Maximum Recommended Controlling Section Size* Specified Brinell Hardness 223---262 248---293 262---311 285---311 302---352 321---363 341---388 w 363---415 w ** Alloy Controlling Section Size. Maximum recommended sizes for flame or induction hardening gearing would be same as above.75 (95) included 4350 Type [ No restriction ] No restriction No restriction No restriction No restriction No restriction No restriction To 23. ] “No restriction” indicates maximum controlling section size is not anticipated to provide any restrictions for conventional size gearing w 900_F(482_C) minimum temper may be required to meet these hardness specifications.5(115) included To 4. Purpose. quenching and tempering temperature considerations. B3. B2.48---0.0 (203) included To 3.0(203) included To 5.55 percent.0 (380) included To 12.6 of the Standard for hardenability considerations.0 (585) incl.0 (305) included To 8. except that carbon is 0. specified hardness.g. but costs should be evaluated due to reduced machinability.] B1. This Appendix presents approximate maximum controlling section size considerations for through hardened (quench and tempered) gearing.0(102) included To 3.Gear Materials and Heat Treatment Manual Appendix B Approximate Maximum Controlling Section Size Considerations for Through Hardened Gearing [This Appendix is provided for informational purposes only and should not be construed as part of AGMA Standard 2004---B89. in (mm) AISI 4140 AISI 4340 To 8.5).0 (640) included To 15. ANSI/AGMA 67 2004---B89 . The controlling section of a part is defined as that section which has the greatest effect in determining the rate of cooling during quenching at the location (section) where the specified mechanical properties (hardness) are required. [ 4350 Type Steel is generally considered equivalent to AISI 4340 for chemical analysis. --.5) of several low alloy steels based on specified hardness range.--.--.--- 10 inch (254) 6 inch (152) Controlling Section: 8 in (203 mm) Diameter Controlling Section: 2 in (50 mm) Face width TEETH TEETH --.--. Table B---1 provides approximate recommended maximum controlling section sizes for oil quenched and tempered gearing (H = 0. then the outside diameter) 32 inch (813) 36 inch (914) Controlling Section: 2 in (50 mm) Rim Thickness Fig B---1 Illustrations of Controlling Section Size ANSI/AGMA 68 2004---B89 .--. Maximum controlling section sizes for rounds greater than 8.--. normal stock allowance before hardening.--.D. and higher hardenability steel may be required.--1.--.Gear Materials and Heat Treatment Manual B4.--. Specified hardnesses able to be obtained with the same type steel (hardenability) is considerably lower.--4 inch (102) 8 inch (203) 36 inch (914) --.--. TEETH TEETH 2 inch (50) --.--.--.--.--.0 inch (205 mm) O. minimum tempering temperature of 900_F(482_C) and obtaining minimum hardness at the roots of teeth. Maximum controlling section sizes versus specified hardness for section sizes to 8. Normalized and tempered heavy section gearing may also require maximum controlling section size considerations if the design does not permit liquid quenching. and published tempering response/hardenability data. General Comments. In---house normalized and tempered/hardness testing experiments are required.5 inch (38) 8 inch (203) --.--.0 inch (203 mm) diameter rounds can also be approximated by use of the “Chart Predicting Approximate Cross Section Hardness of Quenched Round Bars from Jominy Test Results” published in Practical Data for Metallurgists by Timkin Steel Co. Recommendations.--.--. however..--.--12 inch (304) Controlling Section: 2 in (50 mm) Wall Thickness (If the bore diameter is less than 20% of the length of the bore.--. B5. generally require in---house heat treat experiments of larger sections followed by sectioning and transverse hardness testing.--. therefore. The controlling section size in both instances is the section related to the location of gear teeth which governs the rate of heat removed during quench hardening. This Appendix assists in the selection of a grade of carburizing steel to insure that the carburized case has sufficient hardenability to be capable of hardening roots of teeth to meet specified surface hardness requirements. can be evaluated by comparing hardenability to those steels presented to determine the approximate maximum recommended controlling section size (as indicated by the solid line in Fig C---1). The method used is based on steel hardenability considerations and standard hardening procedures used for carburized gearing. The controlling section size of carburized gearing can be determined using the same general principles described in Appendix B for through hardened gearing. ASM Text (1980) AISI 4118 0 5 10 15 20 25 30 35 40 45 Approximate Controlling Section Size. Selection of Steel. Purpose. inch 50 55 60 Fig C---1 Effect of Controlling Section on the Case Hardenability of Carburizing Grades of Steel ANSI/AGMA 69 2004---B89 . mm 400 600 800 1000 200 AISI 9310 AISI 4820 1200 1400 ADEQUATE CASE HARDENABILITY AISI 4320 CASE MAY OR MAY NOT HARDEN AISI 8822 AISI 8620 NO CASE HARDENABILITY Source: The Influence of Microstructure on the of Case ---Carburized Components by Geoffrey Parrish. Gear Materials and Heat Treatment Manual.] can be used for carburized gearing considerations without regard to the fact that gear teeth are machined prior to carburize hardening. Method. To ensure that the steel under consideration has sufficient case hardenability to be capable of satisfactorily hardening the case in the roots of teeth. Fig C---1 should be used. Steels are presented in order of hardenability on the ordinate of Fig C---1. Steels not shown on Fig C---1. Figure C---1 is based on hardenability and controlling section size considerations. C1.Gear Materials and Heat Treatment Manual Appendix C Case Hardenability of Carburizing Steels [This Appendix is provided for informational purposes only and should not be construed as part of AGMA Standard 2004---B89. It may be used in conjunction with design and other considerations to select the appropriate grade of steel. C2. The same examples 0 Approximate Controlling Section Size. Figure B---1 in Appendix B describes examples of how the controlling section size is determined for through hardened gearing when the teeth are cut after heat treating. C3. Heat treat factors which could affect service life include under or over heating. Pitting resistance is influenced by surface finish. stress risers (tool marks and surface finish).2 Pitting. Forging defects which can contribute to premature failure include excessive forging temperature.1 Gear Design. gear class or type. and corrosion. Purpose. inadequate reduction. service conditions and material causes. microstructure. faulty gaskets. Although materials rarely are the principal cause of failure.4 Assembly and Installation. porosity. D2.3 Heat Treatment. Failures related to inadequate maintenance include: contamination of the system. surface decarburization. secondary transformation products. Manufacturing practices which could shorten service life include grinding burns. or improper microstructure after heat treatment. and flaking.7. Improper selection of material can result in inadequate hardness (surface or subsurface) and toughness. Wear is influenced by surface hardness and microstructure. and misalignment. contaminants.7 Material Causes. which is alloy and carbon segregation in banded form. Types of gear failure are pictured in AGMA 110. The most common wear failure modes are adhesion. and bursts from insufficient forging temperature. and bearings. improper grain flow.7.1 Forging Defects. etc.6 Service Conditions. straightening. etc..e. surface hardness.3 Inclusions. D2. chemical deviation. D3. D2. If the service life is less than expected. Wrought materials such as hot rolled bars can have serious banding. microstructure. cold shuts. These factors are gear design. Banding can affect properties. inadequate grounding. decarburization. Gears are generally removed from service due to wear. D2. D2. Failures related to gear design may be due to improper geometry or tolerances. vibration due to inadequate rigidity. improper lubrication. particularly in a carburized case and core. Pitting modes are initial pitting. Casting defects which can contribute to premature failure include shrinkage. plastic flow. insufficient or excessive stock removal after heat treatment. poor radii. etc. cracks. shock or impact loading. inadequate quench. An infrequent cause of fracture initiation is internal non---metallic inclusions which relate to melting practices.2 Manufacture. flakes. improper hardness. tooth thickness. D2. core shift. assembly and installation. sand. D2. Nomenclature of Gear Tooth Failure Modes. and result from excessive sliding and rolling contact stresses. corrosion. Steels can be specified to varying cleanliness levels. This Appendix deals briefly with the causes of gear failures and the types of failures encountered. overload. Service conditions which could adversely effect gear life are excessive temperatures. These usually occur at or above the pitch line. D3. seals. tion criticals in the system causing vibration. D2. loss of lubrication. D2. and spalling. When shorter than expected life is obtained. surface residual stress. a number of factors should be reviewed. Improper assembly and installation are major contributors to premature failures and manifest themselves in excessive loading. abrasive scoring. vibra- ANSI/AGMA 70 2004---B89 . slag. and core hardness. pitting.1 Wear. wear. case depth. manufacture.7. Inadequate stock removal can leave undesirable surface defects. or breakage. case depth. an in---depth investigation should be initiated.] D1. destructive pitting. i. Gear Materials and Heat Treatment Manual.5 Maintenance. and quench cracks. Causes of Lower than Expected Life. corrosion. heat treatment. they can contribute to failure if material selection results in less than the required combination of properties compatible with the design and application. D3. D2. Types of Gear Failures.2 Casting Defects. improper weld repair. pressure angle. maintenance. cracks. etc. D2.Gear Materials and Heat Treatment Manual Appendix D Service Life Considerations [This Appendix is provided for informational purposes only and should not be construed as part of AGMA Standard 2004---B89. and ridging. misalignment. ANSI/AGMA D3. 71 2004---B89 . in heat affected zones of welds or in notch sensitive materials. Overload failures result from misapplication. The majority of breakage failures (90 percent) are due to low and high cycle fatigue. Plastic flow modes are rolling. rippling. Brittle failures may occur in low temperature service. Bending plastic flow occurs when the load exceeds the yield strength of the material. peening.4 Breakage.3 Plastic Flow. and impact loading.Gear Materials and Heat Treatment Manual D3.