BIS Indian standards for Designation of steels | Designation of steel alloys
BIS Indian Standards for 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 the 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 as 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 the 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 writing up to two decimal places.
Example:
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 the largest in composition with the 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