SAE AISI Steel Grade Numbering System

SAE (together with AISI) has devised a numerical reference system for steel and its alloys that can accommodate a complete range of materials but which is incomplete as not all the numbers have yet been allocated a specification⁽¹⁾

The basis for their numbering system is provided below:

The Steel Grades

Plain Carbon Steels	10XX	C <1, Mn <1
Free-Cutting Carbon Steels	11XX	C <1, S >0.05
Free-Cutting Carbon Steels	12XX	C <1, S >0.05, P >0.04
Manganese Steels	13XX	C <1, Mn >1.65
High Hardness Steels	15XX	C <1, Mn 1<1.65
Nickel Steels	23XX	Ni 3.5
Nickel Steels	25XX	Ni 5
Nickel Chromium Steels	31XX	Ni 1.25, Cr 0.65<0.8
Nickel Chromium Steels	32XX	Ni 1.75, Cr 1.07
Nickel Chromium Steels	33XX	Ni 3.5, Cr 1.5<1.57
Nickel Chromium Steels	34XX	Ni 3, Cr 0.77
Molybdenum Steels	40XX	Mo 0.2<0.25
Chromium Molybdenum Steels	41XX	Cr 0.5<0.95, Mo 0.12<0.3
Nickel Chromium Molybdenum Steels	43XX	Ni 1.82, Cr 0.5<0.8, Mo 0.25
Molybdenum Steels	44XX	Mo 0.4<0.52
Nickel Molybdenum Steels	46XX	Ni 0.85<1.82, Mo 0.2<0.25
Nickel Chromium Molybdenum Steels	47XX	Ni 1.05, Cr 0.45, Mo 0.2<0.35
Nickel Molybdenum Steels	48XX	Ni 3.5, Mo 0.25
Chromium Steels	50XX	Cr 0.27<0.65
Chromium Steels	51XX	Cr 0.8<1.05
Chromium Steels	50XXX	Cr 0.5, C >1.0
Chromium Steels	51XXX	Cr 1.02, C >1.0
Chromium Steels	52XXX	Cr 1.45, C >1.0
Chromium Vanadium Steels	61XX	Cr 0.6<0.95, V 0.1<0.15
Chromium Tungsten Steels	72XX	Cr 0.75, W 1.75
Nickel Chromium Molybdenum Steels	81XX	Ni 0.3, Cr 0.4, Mo 0.12
Nickel Chromium Molybdenum Steels	86XX	Ni 0.55, Cr 0.5, Mo 0.2
Nickel Chromium Molybdenum Steels	87XX	Ni 0.55, Cr 0.5, Mo 0.25
Nickel Chromium Molybdenum Steels	88XX	Ni 0.55, Cr 0.5, Mo 0.35
Manganese Silicon Steels	92XX	Cr <0.65, Mn 0.65<0.85, Si 1.4<2
Nickel Chromium Molybdenum Steels	93XX	Ni 3.25, Cr 1.2, Mo 0.12
Nickel Chromium Molybdenum Steels	94XX	Ni 0.45, Cr 0.4, Mo 0.12
Nickel Chromium Molybdenum Steels	97XX	Ni 0.55, Cr 0.2, Mo 0.2
Nickel Chromium Molybdenum Steels	98XX	Ni 1, Cr 0.8, Mo 0.25

The plain carbon steel Table is the most important for defining the physical properties of all untreated carbon steels, including special and alloy steels. The last two digits in any carbon steel will tell you its percentage carbon; i.e. 1040, 1340 and 4140 all have the same carbon content (0.36<0.44, 0.38<0.43 and 0.38<0.43 respectively) and therefore possess similar physical properties (strength, elongation and hardness) before heat treatment or work hardening. However:
1) One or more of the basic alloying elements (manganese, phosphorus and sulphur) are increased in special carbon steels to improve machinability or increase hardness; no other alloying elements are added.
2) One or more of the basic alloying elements (manganese, phosphorus and sulphur) are altered in alloy carbon steels and supplementary elements are added for corrosion resistance and to further improve physical properties through heat treatment and work hardening.

The grade designation is prefixed with a 'G' and suffixed with a '0' (zero) in the UNS format {e.g. 1010 ≡ G10100}.
If the SAE-AISI grade designation is ...
... not prefixed with a character the steel has been manufactured using an open hearth furnace
... prefixed with a 'B' the steel has been manufactured using a Bessemer converter
... prefixed with a 'C' the steel has been manufactured using a crucible furnace
... prefixed with a 'E' the steel has been manufactured using an electric furnace
... suffixed with an 'F' the steel is of the free-cutting type
... suffixed with an 'H' the steel is manufactured to 'hardenability' limits
If the following character is inserted in the middle of the SAE-AISI grade designation ...
... 'B'; the chemical composition includes boron for improved hardness penetration (greater depth)
... 'L'; the chemical composition includes lead for improved machinability

Notes

1. CalQlata has generated a predictive calculator for carbon and alloy steels

Further Reading

You will find further reading on this subject, incl. heat treatment, in our carbon steels web page