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the steel industry uses two major numbering systems to classify steel grades, the american iron & steel institute (aisi) and society of automotive engineers (sae) systems. both the aisi and sae systems primarily use four-digit numeric codes to identify a material’s base carbon or alloy steel; however, some select alloy steels have five-digit codes.
all carbon steels start with a one (1) in both the sae & aisi systems. carbon steels are then further subdivided into four categories by their underlying properties. the four categories are:
· plain carbon steel – 10xx series (containing 1.00% mn maximum)
· resulfurized carbon steel- 11xx series
· resulfurized and rephosphorized carbon steel – 12xx series
· non-resulfurized high-manganese – 15xx series (containing up to 1.65% mn)
the first digit on all other alloy steels (under the sae-aisi system), are classified as follows:
2 = nickel steels.
3 = nickel-chromium steels.
4 = molybdenum steels.
5 = chromium steels.
6 = chromium-vanadium steels.
7 = tungsten-chromium steels.
8 = nickel-chromium-molybdenum steels
9 = silicon-manganese steels and various other sae grades
the second digit of a series typically indicates the concentration of the major element in percentiles. the last two digits of a series indicate the carbon concentration.
sae/aisi designation | type, and composition by weight |
carbon steels | |
10xx | plain carbon (mn 1.00% max.) |
11xx | resulfurized |
12xx | resulfurized and rephosphorized |
15xx | plain carbon (mn 1.00–1.65% max.) |
manganese steels | |
13xx | mn 1.75% |
nickel steels | |
23xx | ni 3.50% |
25xx | ni 5.00% |
nickel-chromium steels | |
31xx | ni 1.25%; cr 0.65%, or 0.80% |
32xx | ni 1.75%; cr 1.07% |
33xx | ni 3.50%; cr 1.50%, or 1.57% |
34xx | ni 3.00%; cr 0.77% |
molybdenum steels | |
40xx | mo 0.20%, 0.25%, or mo 0.25% and s 0.042% |
44xx | mo 0.40%, or 0.52% |
chromium-molybdenum (chromoly) steels | |
41xx | cr 0.50%, 0.80%, or 0.95%; mo 0.12%, 0.20%, 0.25%, or 0.30% |
nickel-chromium-molybdenum steels | |
43xx | ni 1.82%; cr 0.50–0.80%; mo 0.25% |
43bvxx | ni 1.82%; cr 0.50%; mo 0.12%, or 0.35%; v 0.03% min |
47xx | ni 1.05%; cr 0.45%; mo 0.20%, or 0.35% |
81xx | ni 0.30%; cr 0.40%; mo 0.12% |
81bxx | ni 0.30%; cr 0.45%; mo 0.12%; and added boron |
86xx | ni 0.55%; cr 0.50%; mo 0.20% |
87xx | ni 0.55%; cr 0.50%; mo 0.25% |
88xx | ni 0.55%; cr 0.50%; mo 0.35% |
93xx | ni 3.25%; cr 1.20%; mo 0.12% |
94xx | ni 0.45%; cr 0.40%; mo 0.12% |
97xx | ni 0.55%; cr 0.20%; mo 0.20% |
98xx | ni 1.00%; cr 0.80%; mo 0.25% |
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