Classification of Steels1 CLASSIFICATION OF STEELS 1.1 Classification Of Steels On The Basis Of Chemical Composition Steels are materials which contain by mass more iron than any other single element, having a carbon content generally less than 2 % and containing other elements. A limited number of chromium steels may contain more than 2 % of carbon, but 2 % is the usual dividing line between steel and cast iron. Steels are classified on the basis of chemical composition into: (a) Unalloyed steels; and (b) Alloy steels. 1.1.1 Rules for classification The following rules are observed for classifying steels as unalloyed or alloyed: (a) Classification is based on the specified cast analysis; (b) When a minimum value or range is specified for an element, the minimum value is taken for classification; (c) When only a maximum value is specified for manganese, the maximum value is taken for classification; and limiting (d) When a maximum value is specified for elements other than manganese, a value of 0.7 times the maximum value is taken for classification. 1.1.2 Unalloyed steels Unalloyed steels are those steels in which the percentage of each element is less than its value given in Table 1.1. Depending on their carbon content, unalloyed steels are subdivided into: (a) Low carbon steels which contain less than 0.30 % carbon; (b) Medium carbon steels which contain from 0.30 % to 0.60 % carbon; and 60 % carbon. .(c) High carbon steels w hich contain more than 0. die forgeability. and (b) High alloy steels which have a total all oy content greater than or equal to 5 %. 1.. Depending on the total alloy content. The properties of these steels comply with th e limiting values specified in Table 1. lead.) are specified. 1. cold forming.1.2 Quality steels .Unalloyed steels are also subdivided into: ore (a) Plain carbon steels which contain a specified mean manganese content of less than 1 %.070 % and/or bismuth. production and certain grades of general purpose structural steels for which no special requirements (for example cold flangeability. is specified for these requireof special care during (for steels. (b) Quality steels. 1. tellurium or selenium. phosphorus. for example suitability for cold drawing. (b) High manganese carbon steels which contain a specified mean manganese content of m than or equal to 1 %.2. alloy steels are subdivided into: (a) Low alloy steels which have a total alloy content less than 5 %. These steels are not intended for heat treatment.2 Classification Of Unalloyed And Alloy Steels According To Main Quality Classes Unalloyed and alloy steels are subdivided into the following main quality classes: (a) Base steels. etc. 1. etc.2. and (c) Free cutting steels which contain a specified minimum sulphur content of 0.1 Base steels Base steels are unalloyed steels which are manufactured by normal steelmaking operations and which do not require special processing. No other quality requirement. and (c) Special steels.2.1.3 Alloy steels Alloy steels are those steels in which the percentage of each element is equal to or greater than its limiting value given in Table 1. This class of steel includes steels for flat products commercial quality. improved cold forming properties.) to achieve. special quality characteristics such as improved resistance against brittle fracture. etc.Quality steels are unalloyed and alloy steels which example by grain size control. etc. improv ement of surface finish. decrease of phosphorus and sulphur content. . in comparison with base steels. 1. special q uality characteristics such as controlled hardenability. steels for flame and induction hardening. and tool steels. and steels with a specified electrical conductivity less than 9 S/m. or particularly low contents of non -metallic inclusions.2 Alloy special steels This class of steel includes bearing steels. steels for flat products of drawing quality.3 Special steels Special steels are unalloyed and alloy steels which require precise control of chemical composition and special care in production to achieve. phosphorus and/or sulphur. steels for quenching and tempering other than those covered by 1. steels for quenching and tempering. These steels are cleaner than quality steels. . 1.2. case hardening steels. heat and creep resisting steels. 1. and steels for rails.2.2.3.1 Unalloyed special steels This class of steel includes case hardening steels.2 Alloy quality steels This class of steel includes certain weldable fine grain str uctural steels with high yield strength.2. 1.2.1.3. free cutting steels. 1.2.3. specified impact strength in the heat treated condition. steels with a specified electrical conductivity equal to or more than 9 S/m. in comparison with quality steels.1 Unalloyed quality steels This class of steel includes cold heading and cold extruding steels not intended for heat treatment.2. certain steels for nuclear reactors. steels in which copper is the only alloying element.2. nitriding steels. and tool steels. . steels for quenching and tempering. special structural steels. steels with special physical properties. steels for flame and induction hardening. stainless steels. 2. Steel Names Based on Letter Symbols. U.. Definition and Classification of Grades of Steel. 5. Steels ⎯ Classification ⎯ Part 1: Classification of Steels into Unalloyed and Alloy Steels Based on Chemical Composition. Ohio. Materials Park. ISO 4948-1:1982.2 REFERENCES Characteristics. . Steels ⎯ Classification ⎯ Part 2: Classification of Unalloyed and Alloy Steels According to Main Quality Classes and Main Property or Application 3. 1990. ISO 4948-2:1981. 4. DIN EN 10020:2000 .S. ISO/TR 4949:1989. 1. ASM International. 1. vol. ASM Handbook.A. . 80 Other specified elements (except C.40 1.651) 0.40 0.10 0. Note: For each alloying element.08 0. N.Limiting value Table 1.30 0.10 0.1 Symbol Boundary between unalloyed and alloy steels Al Specified element Bi B Name Cr Co Cu Pb Mn Mo Ni Nb Se Si Te Ti W V Zr - % by mass 0. the specified.10 0.05 0. the limiting value is 1.10 0.30 0.50 0.10 0. calculated or actual cast analysis value is expressed to the same number of decimal places as the corresponding limiting value shown above.0008 0. P and S) (each) 1) %.10 0.10 0. .05 0.05 0.06 0.05 Aluminium Bismuth Boron Chromium Cobalt Copper Lanthanides (each) Lead Manganese Molybdenum Nickel Niobium Selenium Silicon Tellurium Titanium Tungsten Vanadium Zirconium When only a maximum value is specified for mangan ese. . on a longitudinal ISO V -notch test piece Maximum Rockwell hardness Maximum carbon content a = thickness of the bend test piece.007 % m . Maximum phosphorus content Maximum sulphur content Maximum nitrogen content 1) properties of base steels ≤ 16 ≤ 690 MPa ≤ 16 ≤ 360 MPa ≤ 16 ≤ 26 % m ≥ 3 ≤ 16 ≥1a1) ≥10 ≤ 16 ≤ 27 J ≥ 3 ≤ 16 - ≥ 60 HRB ≥ 0.Limiting value Table 1.050 % ≥0.10 % ≥0.050 % ≥ 0.2 Limiting values for specified ≥3 Specified properties Thickness ≥3 ≥3 Minimum tensile strength Minimum yield strength Minimum percentage elongation after fracture (Lo = 5.65⋅√So) Minimum diameter of bending mandrel Minimum impact strength at 20 °C.
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