The American Iron and Steel Association uses three numbers to represent various standard grades of malleable stainless steel. These include:
(1) Austenitic stainless steel is marked with 200 and 300 series numbers. For example, some common austenitic stainless steels are marked with 20 1, 304, 3 16, 3 10.
(2) Ferritic and martensitic stainless steels are represented by 400 series numbers.
(3) ferritic stainless steel is marked with 430 and 446, and martensitic stainless steel is marked with 4 10, 420 and 440C.
(4) Duplex (austenite-ferrite), stainless steel, precipitation hardening stainless steel and high alloy with iron content less than 50% are usually named by patent names or trademarks.