Metals Codes -4:Stainless Steel Codes
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The UNS designation system for stainless steel follows the AISI standard . By prefacing it with an S and adding two more digits to the end it becomes a UNS number. For example AISI/SAE 304 stainless steel is converted to S30400 UNS

Key to the AISI/SAE stainless steel numbering system

Austenitic Stainless Steels

  • The first digit is "3" as in 3xx
  • The second and third digits do not correlate to any particular chemical combination or process. However, in general, chromium content increases with the last two-digit number.

Martensitic and Ferritic Stainless Steels

  • The first digit is always "4" as in 4xx
  • The second and third digits do not correlate to any particular chemical combination or process. However, in general, chromium content increases with the last two-digit number.

Precipitation Hardening Stainless Steel

  • The first digit is "6" as in 6xx

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label: standards, UNS, AISI,ASTM, ASE, coding, steel, stainless steel, tool steel, aluminum, copper, austenetic, martensitic, ferritic, precipitatin hardening