Steel designations defined by of the American Iron and Steel Institute. AISI carbon and alloy steels are essentially the same as those designated by the Society of Automotive Engineers (SAE). The AISI system is more comprehensive than the SAE in that letters precede the alloy number indicating the manufacturing method: A represents basic open-hearth alloy steel, B acid Bessemer carbon steel, C basic open-hearth carbon steel, CB either acid Bessemer or basic open-hearth carbon steel, E electric furnace alloy steel.