A36 is a low carbon steel. Low carbon steels are classified by having less than 0.3% carbon by weight. This allows A36 steel to be easily machined, welded, and formed, making it extremely useful as a general-purpose steel. The low carbon also prevents heat treatment from having much of an effect on A36 steel. A36 steel usually has small amounts of other alloying elements as well, including manganese, sulfur, phosphorus, and silicon. These alloying elements are added to give A36 steel its desired chemical and mechanical properties. Since A36 does not contain large amounts of nickel or chromium, it does not have excellent corrosion resistance.
Unlike most AISI grades such as 1018, 1141, or 4140, American Society for Testing and Materials (ASTM) A36 steel is not designated by chemical composition. Instead, A36 is designated by mechanical properties. This means that while most grades must have added alloys that fit between certain percentages, A36 must meet specific mechanical standards. For example, steel bars and plates must have a minimum yield strength of 36,000 pounds per square inch. While there are some chemical composition requirements that A36 steel must adhere to, the most important characteristic is the yield strength requirement.
