Carbon Steel Coding

The AISI and the SAE have designed a four digit code to assign to all carbon and alloy steels to show its standard wrought steel composition. In carbon steel grades the last two digits indicate the nominal carbon content. When the code 10 appears in the first two digits of the code (ex. 10xx) the steel is plain carbon steel. If the code is 11xx it is resulfurized, 12xx refers to resulfurized and rephosphorized while 15xx refers to nonresulfurized with a Mn content of over 1 percent.

The presence of the letter L between the second and third digits of the code indicates that it is a leaded steel. The letter B indicates a boron steel. Cast-carbon steels will usually be specified by grade, such as A, B, or C. The A grade (also LCA, WCA, AN, AQ, etc.) has a 0.25 percent carbon content and a maximum of 0.70 percent of Mn. B-grade steel has a 0.30 percent carbon content and a Mn content of 1.00 percent while C-grade steel has a 0.25 percent carbon content and 1.20 percent of Mn. The mixture of carbon and manganese in a steel is used to improve the steel’s strength, toughness, and weldability. Cast carbon steels are specified to ASTM A27, A216, A352, or A487.

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