2 July 2022

Steel Numbering System | AISI – SAE Classification System AISI XXXX | Steel Nomenclature | Steel Designation

Steel Numbering System

AISI – SAE Classification System AISI XXXX

American Iron and Steel Institute (AISI)

  • classifies alloys by chemistry
  • 4 digit number

                         AISI XXXX

–1st number is the major alloying element

–2nd number designates the subgroup alloying element OR the relative percent of primary alloying element.

–last two numbers approximate amount of carbon  (expresses in 0.01%)

 

AISI – SAE Classification System

  • letter prefix to designate the process used to produce the steel

 –E = electric furnace

–X = indicates permissible variations

  • If a letter is inserted between the 2nd and 3rd number

–B = boron has been added

 –L = lead has been added

  • Letter suffix

–H = when hardenability is a major requirement

  • Other designation organizations

–ASTM and MIL

AISI/SAE most common, also have Unified Numbering System (UNS) and ASTM

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