Metals Codes - 3: The AISI/SAE Steel Designation System
Library | Start Page | Previous Page| Next Page
WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.

As mentioned on the previous page the UNS system is derived from the older AISI/SAE system. However since the older system has been used for such a long period of time and since all machinists do not recognize the UNS coding, the AISI/SAE system is defined here as well. With one exception the first digit signifies the major alloy used in the steel. Carbon steels are not alloyed.

Key to the AISI/SAE steel numbering system

The first two numbers in this designation signify the primary alloy(s) of the steel. The next two numbers in the designation signify the amount of carbon present in the steel.

  • Carbon Steels:
    • The first digit is "1" as in 10xx, 11xx, and 12xx
    • The second digit describes processing: "1" is resulfurized and "2" is resulfurized and rephosphorized.
  • Manganese Steel:
    • The first digit is "1" as in 13xx and is, indeed, a carbon steel. However, since manganese is a normal by-product of carbon steel making the AISI/SAE has decided not to classify it as an alloy steel.
    • The second digit is always "3"
  • Nickel Steel:
    • The first digit is "2" as in 23xx and 25xx
    • The second digit designates the percentage of nickel in the steel.
  • Nickel-Chromium Steel:
    • The first digit is "3" as in 31xx, 32xx, and 33xx,
    • The second digit designates the percentage of nickel and chromium in the steel .
  • Molybdenum Steels:
    • The first digit is "4" as in 40xx and 44xx.
    • The second digit designates the percentage of molybdenum in the steel.
  • Chromium Steel:
    • The first digit is "5" as in 51xx and 52xx
    • The second digit designates the percentage of chromium in the steel.
  • Chromium-Vanadium Steel:
    • The first digit is "6" as in 61xx
    • The second digit designates the percentage of chromium and vanadium in the steel.
  • Tungsten-Chromium Steel:
    • The first digit is "7" as in 72xx
    • The second digit designates the percentage of tungsten and chromium
  • Silicon-Manganese Steel:
    • The first digit is "9" as in 92xx
    • The second digit designates the percentage of silicon and manganese in the steel.
  • Triple Alloy Steels:
    • These steels contain three alloys
    • The first digit can be "4", "8", or "9" depending on the predominate alloy
    • The second digit designates the percentage of the reaming two alloys.