SAE steel grades

The Society of Automotive Engineers (SAE) designates SAE steel grades. These are four digit numbers which represent chemical composition standards for steel specifications. The American Iron and Steel Institute (AISI) originally started a very similar system. Over time they used the same numbers to refer to the same alloy, but the AISI system used a letter prefix to denote the steelmaking process. The prefix "C" denoted open-hearth furnace, electric arc furnace or basic oxygen furnace, while "E" denotes electric arc furnace steel.

Prior to 1995 the AISI was also involved, and the standard was designated the AISI/SAE steel grades. The AISI stopped being involved because it never wrote any of the specifications.

Carbon and alloy steel

Carbon steels and alloy steels are designated by a four digit number, where the first digit indicates the main alloying element(s), the second digit indicates the secondary alloying element(s), and the last two digits indicate the amount of carbon, in hundredths of a percent by weight. For example, a 1060 steel is a plain-carbon steel containing 0.60 wt% C.

An "H" suffix can be added to any designation to denote hardenability is a major requirement. The chemical requirements are loosened but hardness values defined for various distances on a Jominy test.