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Designation of steel on the basis of
chemical composition
1) Unalloyed steels
X C Y Z
- X = 100 times the average % of C
- C = Carbon
- Y = 10 times the average % of Mn
- Z = Special characteristics
Example:
25 C5 B0 = Semi killed steel with 0.25% C,
).5% Mn, Resistance to brittle fracture grade
BO.
2) Unalloyed tool steel
X T Y
- T = Tool steel
- X = 100 times the average % of C
- Y = 10 times the average % of Mn
Example:
80 T 11 = Unalloyed tool steel, 0.80% C, 1.1%
Mn
3) Unalloyed free cutting steel
X C Y W W1 Z
- W = Element which makes the steel free
cutting
- W1= 100 times the % of element
present.
- X, C, Y and Z have the same meanings same
as above
Example:
20 C12 Pb15 T14 = Free cutting steel with
0.2% C, 1.2% Mn, 0.15% Pb, hardened and
tempered.
4) Alloy steels
a) Low and medium alloy steels (alloying
elements not exceeding 10%)
- Ist symbol - 100 times the average % of C
- 2nd, 4th, 6th symbols etc = Elements
- 3rd, 5th, 7th symbols etc. = % of
elements, multiplied by factors as follows
| Element |
Multiplying factor |
| Cr, Co, Ni, Mn, Si and W |
4 |
| Al, Be, V, Pb, Cu, Nb, Ti,
Ta, Zr and Mo |
10 |
| P, S, N |
100 |
Example:
40 Ni 8 Cr 8 V 2 = Hot rolled steel with 0.4%
C, 2% Cr, 2% Ni and 0.2% V.
b) High alloy steels (total alloying
elements >10%)
Example:
X 10 Cr18 Ni9 S3
X = High alloy steel
10 = 0.10% C
Cr 18 = 18% Cr
Ni 9 = 9% Ni
S 3 = Pickled condition
c) Alloy tool steels
Example:
XT 98 W6 Mo5 Cr4 V1
XT = High alloy tool steel
98 = 0.98% C
W 6 = 6% Tungsten
Mo 5= 5% Molybdenum
Cr 4 = $% Chromium
V1 = !& Vanadium
d) Free cutting alloy steels
Example:
X 15 Cr25 Ni15 S40
X = High alloy steel
15 = 0.15%C
Cr 25 = 25% Chromium
Ni 15 = 15% Nickel
S 40 = 0.4% Sulphur (S introduces free
cutting qualities)
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