The AISI / SAE Steel numbering system has some logic to it that will help you identify some key points right away even if you are not familiar with a particular grade.
- The first two numbers indicate the alloy according the the chart below.
- The last two numbers indicate the amount of carbon in the alloy, where the digits “10”, for example, represent 0.10% carbon.
Example AISI/SAE 1020
- the first two digits indicate this is plain carbon steel.
- the last two digits indicates that the steel contains approximately 0.20% carbon.
Example AISI/SAE 4340
- the first two digits indicate this is a Nickel-Chromium-Molybdenum alloy steel
- the last two digits indicate that the steel contains approximately 0.4% carbon
| AISI/SAE Steel Numbering System |
| Carbon steels | 10XX | Plain carbon, Mn 1.00% max |
| 11XX | Resulfurized free machining | |
| 12XX | Resulfurized/rephosphorized free machining | |
| 15XX | Plain carbon, Mn 1.00-1.65% | |
| Manganese steel | 13XX | Mn 1.75% |
| Nickel steels | 23XX | Ni 3.50% |
| 25XX | Ni 5.00% | |
| Nickel-chromium steels | 31XX | Ni 1.25%, Cr .65-.80% |
| 32XX | Ni 1.75%, Cr 1.07% | |
| 33XX | Ni 3.50%, Cr 1.50-1.57% | |
| 34XX | Ni 3.00%, Cr .77% | |
| Molybdenum steels | 40XX | Mo .20-.25% |
| 44XX | Mo .40-.52% | |
| Chromium-molybdenum steels | 41XX | Cr .50-.95%, Mo .12-.30% |
| Nickel-chromium-molybdenum steels | 43XX | Ni 1.82%, Cr .50-.80%, Mo .25% |
| 47XX | Ni 1.05%, Cr .45%, Mo .20-.35% | |
| Nickel-molybdenum steels | 46XX | Ni .85-1.82%, Mo .20-.25% |
| 48XX | Ni 3.50%, Mo .25% | |
| Chromium steels | 50XX | Cr .27-.65% |
| 51XX | Cr .80-1.05% | |
| 50XXX | Cr .50%, C 1.00% min | |
| 51XXX | Cr 1.02%, C 1.00% min | |
| 52XXX | Cr 1.45%, C 1.00% min | |
| Chromium-vanadium steels | 61XX | Cr .60-.95%, V .10-.15% |
| Tungsten-chromium steels | 72XX | W 1.75%, Cr .75% |
| Nickel-chromium-molybdenum steels | 81XX | Ni .30%, Cr .40%, Mo .12% |
| 86XX | Ni .55%, Cr .50%, Mo .20% | |
| 87XX | Ni .55%, Cr .50%, Mo .25% | |
| 88XX | Ni .55%, Cr .50%, Mo .35% | |
| Silicon-manganese steels | 92XX | Si 1.40-2.00%, Mn .65-.85%, Cr 0-.65% |
| Nickel-chromium-molybdenum steels | 93XX | Ni 3.25%, Cr 1.20%, Mo .12% |
| 94XX | Ni .45%, Cr .40%, Mo .12% | |
| 97XX | Ni .55%, Cr .20%, Mo .20% | |
| 98XX | Ni 1.00%, Cr .80%, Mo .25% |