MARAGING STEELS FOR AERO SPACE APPLICATIONOUT LINE 27 April 2011 Introduction Applications Discussions Landing Gear Material Effect of alloying elements Physical metallurgy Strengthening Mechanism Conclusions 2 WHAT IS STEEL? Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, manganese, chromium, vanadium, vanadium, and tungsten. tungsten. 27 April 2011 3 27 April 2011 4 .WHAT IS MARAGING STEEL? Maraging steels are primarily based on FeFe-Ni system and derive their properties due to combination of two solid state reactions: reactions: MAR+AGING. martensite. Meaning martensitic transformation from austenite and aging of the resulting martensite. gear.APPLICATIONS In Aerospace Aircraft forging (Eg. wing fittings) Solid-propellant missile cases Solid Jet-engine starter impellers Jet Aircraft arrestor hooks Torque transmission shafts Aircraft ejector release units 27 April 2011 5 . Undercarriage parts/landing (Eg. gear. In Tooling and Machinery Punches and die bolsters for cold forging Extrusion press rams and mandrels Aluminium die-casting and extrusion dies dieCold reducing mandrels in tube production ZincZinc-base alloy die-casting dies dieMachine components: gears 6 27 April 2011 . or zipper etc) etc) 27 April 2011 7 .Structural Engineering and Ordnance Lightweight portable military bridges Ordnance components Fasteners (a button. hook. MORPHOLOGIES OF MARTENSITE Lath Martensite Plate Martensite Concentration Low C+ Alloying Elements High C+ Alloying Elements Shape Strip Plates Temperature High Transition Temperature Low Transition Temperature 27 April 2011 8 . 19 Normal component of strain 0.09 27 April 2011 Maraging steel Fe-Ni Martensite BCC Structure Soft Soft & Ductile Aging (Precipitates of Intermetallic compounds) increases ductility & Toughness Shear component of strain 0.05 9 .20 Normal component of strain 0.COMPARISON BETWEEN CONVENTIONAL TEMPERED MARTENSITE AND MARAGING STEEL Conventional Tempered Martensite Fe-C Martensite BCT Structure Hard & Brittle Tough and less ductile Tempering increases ductility & Reduces Strength Shear component of strain 0. 27 April 2011 10 . 27 April 2011 11 . 27 April 2011 12 . SELECTION CRITERIA FOR AERONAUTICAL vs. No. Nomenclature Aeronautical Safe-life design Fatigue Crack Growth Damage Tolerant Design High > 60% Lighter Specific strength (Y.S/Density) Low Consistent Good High General Engineering Materials Infinite Life Design Static Mech. 1. 6. 4. 3. GENERAL ENGINEERING MATERIALS Sl. Properties Low < 40% for land based Turbines Heavy UTS High Variable Poor Low Design philosophy Efficiency Weight Strength Safety Factor Performance Reliability Confidence level 27 April 2011 13 . 2. 5. 8. 7. LANDING GEAR MATERIAL Steel ± Aermet Maraging Steel Titanium alloys Magnesium alloys Aluminium alloys 27 April 2011 14 . High Y.S.T.S High Young¶s Modulus Good ductility in both directions.PROPERTY REQUIREMENTS FOR LANDING GEAR Requirements Lower Aircraft weight Lower non damaging permanent set during take-off & landing Maximum stress levels in plastic range Better dynamic response as sliding member Deformation rather than fracture outside the design envelope & landing gear Resistance to crack initiation & growth Resistance from salt environments 27 April 2011 Property Low density High Y.S./U. longitudinal + transverse High Fatigue strength High Resistance to Stress Corrosion Cracking 15 . workable /cold worked upto 80-90% without 80cracking Easily fabricated and Good Weldability April 2011 Carbonising & Nitriding 27 16 .Minimum Distortion Low Carbon Martensite: Fe-Ni Martensite (BCC).SPECIFIC CHARACTERISTICS OF MARAGING STEEL Ultra high strength at room temperature and retain strength up to 350 C Combination of strength & Ductility Superior Fracture Toughness Simple Heat Treatment Cycle . Fesoft. 27 April 2011 17 . PROCESS FLOW CHART (MDN 250A) Primary Melting 480 mm ingot CONDITIONING VIM VAR FORGING Remelting 550 mm 230 mm ULTRASONIC TESTING HEAT TREATMENT STRAIGHTENING MACHINING SAMPLE PREPARATION HEAT TREATMENT TESTING 27 April 2011 215 mm UPSETTING 25 mm HEAT TREATMENT TESTING -HCF -LCF -IMPACT INSPECTION PACKING & DISPATCH 18 . 50 Minimum 8J Minimum 48 Min.MECHANICAL PROPERTIES OF MARAGING STEEL MDN 250A PROPERTIES A.2%PS (MPa) % El (4D) NTS/UTS Shear Strength (MPa) Impact Strength at RT Torsional Shear Strength (MPa) Hardness Rc Macrostructure 27 April 2011 TEST RESULTS SPECIFIED 1760-1825 1688-1768 11-13 1.0 min. 1.58 977 to 1063 19 to 25.8J 1378 to 1411 51 to 54 Satisfactory Record 1655 6. 215mm SIZE STAGE Tensile Properties UTS(MPa) 0.53 TO 1. 19 . Upto 1. RA below 1% Nonmetallic inclusion Good .0x 107 cycles min.5 J 15-20 - Forgeability Physical properties B. 20 Low Cycle Fatigue at RT Smooth 1448 Mpa 27 April 2011 1059 to 1642 .Microstructure Prior austenite grain size 5±1 ASTM No.0x 103 cycles min. 1.0x 107 cycles min. E= 185GPa 28.10.37x 107 1.83x 107 Upto 1.96 gm/cm3.94x 106cm/cm/ C density 7. 1. 25mm SIZE STAGE: Impact Strength at RT Low Temperature Tests Impact strength at -70 C (J) High Cycle Fatigue at RT Smooth 680 Mpa Notch 350 MPa 8 27 J 48 min. QUALITY ASSURANCE STEPS DURING PROCESSING PROCESS STEPS Raw Material Control QUALITY ASSURANCE Material control /Approval of Sources Comparison with Specification Inspection & Analysis Supplier Test Certificate Crucible Condition Melt Chemistry Electrode Surface & soundness Leak Rate Ultimate Vacuum level Melt Rate Ingot Surface 21 PROCESSING Primary Melting (AAM/AIM/VIM) Secondary Melting (VAR/ESR) 27 April 2011 . PROCESS STEPS Forging QUALITY ASSURANCE Furnace Atmosphere Heating Cycle Forge Finish Temperature Macro & Ultrasonic Test Temperature control Inspection & Removal of Defects Heating cycle Furnace Atmosphere Rolling Heat Treatment Solution Annealing (H) 820 10 C/9½ hrs/AC Aging (X) 480 5 C/3 hrs/AC Testing & Evaluation Test Piece Dimension Load Cell Calibration Metallurgical Evaluation Verification of Results Consistency in Melt Batches 22 27 April 2011 . Go to matrix to free the Mo for ppt (Co-Mo combined effect) Principal Strengthener Ni3Mo Precipitate Fe2Mo Precipitate 23 <2% > 9% Strength Microsegragation Inadequate Toughness .EFFECT OF ALLOYING ELEMENTS Name of the Element Nickel (Ni) 8-19% Content Low < 8% Toughness Content High > 19% Austenite in matrix (retained µ ¶) Austenite does not merge with matrix Toughness > 20% Toughness Effect on Properties Tough-Ductile Martensite matrix Primary strengthener Ni3Mo Precipitate Cobalt (Co) 8-20% Mo 2-9% 27 April 2011 < 8% Strength Principal Strengthener Raises Ms temp. Name of the Element Aluminium (Al) (0. TiCN ppt at GB Reduce fatigue Most determined element Calcium is added to reduce sulphur effect Tolerated with no problem Sulphur (S) 0.15% or less) Boron (Bo) & Zirconium (Zr) Si & Mn Carbon (C) 0. Carbo-nitrides Inclusions at GB Embrittlement TiC.1% reduce plasticity Good Bad More carbides inclusions Carbides.03% max Content Low Content High Effect on Properties Deoxidizer Charpy Impact No Strengthening Effect Little effect on Mechanical prop Enhance resistance to strength corrosion Impact strength Si above 0.10% max Reduce properties in transverse directions Phosphorous (P) 27 April 2011 24 . PHYSICAL METALLURGY 27 April 2011 IronIron-Nickel Binary Phase Diagram 25 . 27 April 2011 26 . 27 April 2011 27 . 27 April 2011 28 . 1976 = O + i + K1 d-1/2 + K2 l-1/2 + Gbe1/2 + Gb/L Gb/L f Where. are constants 27 April 2011 f 29 . = Flow stress O = Friction stress Solid Solution Hardening component i= d = Grain size l = lath packet size G = Shear Modulus b = Burger Vector L = Inter particle spacing e = Dislocation density .STRENGTHENING MECHANISM Norstrom Equation. 1 - Cr 11 1 Al 0.1 0.5W 2.2 - 18 18 10 3 8 8 9 12 5 5 A 0.4 1.SOME RECENTLY DEVELOPED MARAGING STEEL Alloy Nominal composition Yield strength (in MPa) Others 4.4 1.1 0.1 Si 1780 1700 1600 1500 Ni Co-Free Korean W250 Inco T250 Ni-Cr Russian Ni-Cr-Si Indian (DMR 1700) Ni-Co-Mo-Cr Russian Indian 27 April 2011 Co - Mo 3 2 - Ti 1.1 11 11 A - - 1700 30 . 3. 2. The alloy has been successfully developed. 4. The programme has been satisfactorily completed and material supplied for end use and satisfactory performance feedback obtained from users. Consistency among melts and Integrity within each melt has been achieved and the material was found to have comparable properties with that of imported material.CONCLUSIONS 1. 27 April 2011 31 . Indigenization and supply of this strategic alloy has helped self reliance in ISRO and DRDO programmes. produced commercially and type certified. com http:/en.org Presentation given by Mr. Ashok Kumar. HYD. DRDO.keytometals. Additional Regional Director.wikipedia . 27 April 2011 32 .REFERENCES ASM Hand Books http://www. 27 April 2011 33 .