By the 1920's the Society of Automotive Engineers had developed a system for identifying the most commonly used steel alloys by number. Generally the number had four digits, but five and even six were possible.
The first digit indicates the principal alloying element:
The second digit indicates the approximate percentage of the predominant alloying element. If the percentage is greater than 9%, this second digit becomes two digits. The figure given was nominal. For example, the digit in the specification number might be "2," but the actual percentage in the alloy 1.5%. Actual composition and tolerances were given on the society's specification sheets for each alloy.
The last two digits indicate the carbon content in hundreths of a percent. If the carbon content exceeds 1%, instead of two digits there will be three.
|2340||nickel steel, about 3% nickel, about 0.40% carbon|
|71360||tungsten steel, about 13% tungsten, about 0.60% carbon|
|3245||nickel-chromium steel, about 2% nickel, about 0.45% carbon|
|52100||chromium steel, about 2% chromium, about 1% carbon|
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Last revised: 4 September 2013.