BIS Indian standards for Designation of steels | Designation of steel alloys

BIS Designation of steels

Bureau of Indian Standard shortly BIS uses the following designation. Symbolic Letters and Numbers to designate the steel grade (e.g. Mechanical, Physical, and Chemical). The standard IS No. is 7598:1990.

Classification of Steel names

For the purpose of designation, steels are classified into two types. They are:

• Group 1
• Group 2

Group 1 – According to their application and Mechanical or Physical properties

Group 2 – According to their Chemical composition

Principal symbols:

G – Steel casting

P – Steel for pressure purposes

D – Flat products for cold forming

R – Rails

nnn – specified minimum yield strength for the smallest thickness range

Cnn – Cold rolled

Dnn – Hot rolled for direct cold forming

Xnn – Product where rolled conditions are not specified

Additional Symbols:

B – Gas bottles

M – Thermo-mechanically rolled

N – Normalized rolled

Q – Quenched / Tempered

S – Simple pressure vessels

T – Tubes

G – Other

H – High Temperature

L – Low Temperature

R – Room Temperature

X – High and Low temperature

Designation of Plain carbon steels

These are denoted like x, C, y

Where,

x – Number 100 times the average percent of carbon

y – Number 100 times the average percent of Manganese

Example:

30C8

Where,

30 = 100 times average % of Manganese

8 = 100 times average % of Carbon

Average % of Carbon = 30/100 = 0.3%

Average % of Manganese = 8/100 = 0.08%

Actual means, the actual carbon % is not 0.3, but varies between 0.2 – 0.4%, so that the average becomes (0.2 + 0.4)/2 = 0.3%, and

Manganese from say 0.07 – 0.09%, so that the average (0.07+0.09)/2 = 0.08%

Designation of Alloy Steels

Alloy steels are denoted by arranging the alloying elements in the descending order of their proportion, and the average % of each element is shown with its chemical symbol before that number. The letter C is omitted here, and just the number is written to denote carbon percentage. When an alloying element is less than 1% that element is denoted by an underline, after written up to two decimal places.

Example:

An alloy steel of the following composition is to be designated

Carbon = 0.13 to 0.17%; Silicon = 0.1 to 0.4%; Chromium = 0.5 – 0.8%; Manganese = 0.4 – 0.5%

Here,

Carbon varies from 0.13 to 0.17

Therefore average % of C = (0.13 + 0.17)/ 2  = 0.15

Among the other alloying elements, Chromium is largest in composition with average % being 0.5 to 0.8%

Therefore average % of Cr = (0.5 + 0.8) / 2 = 0.65

Therefore the above example’s designation will be 15 Cr 65

Note: since it is less than 1% it is shown by an underline

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