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

Tags: BIS designation of steel, BIS designation of materials, Bureau of Indian Standards for steel, Designation system of steel, Designation of steel as per BIS, Designation of steel alloys