Designation of steels

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Designation of steels

Bureau of Indian Standards (BIS) designates the various grades of steels by a system of codification which bears direct relationship with the important characteristics of steel such as tensile strength, chemical composition. physical and surface conditions. According to this method a particular grade designation would be applicable to certain steel only. Hence steel may be designated by a group of symbols indicating the important characteristics.

(i) 1025.     Indicates C-25 which is plain carbon steel,

(ii) 1112.     It is a free cutting steel having percentage

C = 0.13 Max.

Mn = 0.7 – 1.0 %

P = 0.07 – 0.12 %

S = 0.16 – 0.23%

(iii) 4145.     It is Cr-Mo – steel having percentage

C = 0.33 – 0.38%

Mn = 0.7 – 0.9%

P or S = 3.025%

Si = 0.2 – 0.35%

Cr = 0.81 – 1.1 %

Mo = 0.18 – 0.25%

(iv) 8650.     It is Ni-Cr-Mo alloy steel having percentages

Ni = 0.4 – 0.7%

Cr = 0.4 – 0.6%

Mo = 0.15 – 0.25%

(v) 3145.     It is a Ni-Cr steel having

Ni = 0.3 – 0.35%

Cr = 0.4 – 0.5%

(vi) 2330.     It is a Ni-steel having percentages

C = 0.28 – 0.33%

S = 0.04%

Mn = 0.5%

Si = 0.02 – 0.35 %

Ni = 3.25 – 3.75%

(vii) 5150.     It is a Cr-Steel

Following symbol recommended to be used to indicate heat treatment given to steel and is to be suffixed at the end of normal symbol of steel.

(1) Annealed and softened                          a

(2) Case carburized                                    c

(3) Hard, drawn, cold reduced                      d

(4) Hot rolled                                              h

(5) Normalized                                            n

(6) Spherodised                                          0

(7) Patented                                                p

(8) Hardened and Tempered                         q

(9) Stress relieved                                       s

(10) Tempered                                             t

Steel Quality

Following symbols should be recommended to be suffixed with the normal steel symbol to indicate the steel quality

(1) Non-ageing quality                                                                 A

(2) Stabilizing against stress corrosion and inter-annular attack       E

(3) Control cooled ensure freedom from flakes                               L

(4) Fully-killed (deoxidized)                                                           D

(5) Semi-killed                                                                             D2

(6) Rimming quality                                                                       R

(7) Grain size controlled                                                                 G

(8) Hardenability controlled                                                             H

(9) Inclusion controlled                                                                    I

(10) Structural homogeneity guaranteed by macro- structure test        M

Carbon Tool Steel (Annealed)

Carbon tool steel in annealed condition is explained as below with designation and uses.

C-60                   Spindles for machine tools, coupling, crank shaft axles and pinions.

C-65                   Small washers and thin stamped parts.

C- 70                  Buffer spring shock absorbers.

C- 75                   Light flat, springs formed from annealed stock.

C-75-C-85            Flat and coils springs for automobiles and railway vehicles.

C-50 to C-113       Springs made from small flat section.

Plain Carbon Structural Steel

Designation and Uses

St-42           For bridge and building construction, railway rolling stock, screw spikes and oil well castings.

St-44           Pressure vessels, fasteners, value fittings for compressed gas cylinders and railway rolling stock.

St-47            For railway rolling stock, pressure parts of marine and land boilers and rivets for air receivers.

St-50             For mines, forgings of marine and engine parts.

St-52-54         For railway wheels, electric tramways cars.

Reference Introduction to basic Manufacturing Processes and Workshop Technology by Rajender Singh.

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