


SERIES CODE STEEL TYPE
1XXX
Plain
carbon (non alloy) steel
13XX
Manganese
steel
2XXX
Nickel
alloy steels
23XX
3.5%
Nickel
25XX
5.0%
Nickel
3XXX
Nickel/Chrome
steels
4XXX
Molybdenum
steels
40XX
Carbon/Moly
41XX
Chrome/Moly
43XX
Chrome/Moly/Nickel
46XX
or
48XX
Moly/Nickel
5XXX
Chromium
alloy steels
51XX
Low
Chromium content
52XX
Medium
Chromium content
53XX
High
Chromium content
6XXX
Chromium/Vanadium
alloy steels
86XX
or
87XX
Nickel/Chromium/Moly
alloy steels
92XX
Manganese/Silicon
alloy steels
The American Iron and Steel Institute (AISI) also developed a letter/number code, based upon the alloy's hardening medium, content, or use.
LETTER CODE STEEL TYPE
A******************Air-hardening
steels
D******************Die
steel alloys
F******************Carbon/Tungsten
alloys
H******************Hot
work alloys
L******************Low
alloy
M*****************Molybdenum
alloys
O*****************Oil
hardening steels
P******************Mold
steel alloys
S******************Shock
resistant alloys
T******************Tungsten
alloys
W*****************Water
hardening steel