The American Iron and Steel Society uses three digits to mark a variety of standard levels of forged stainless steel.
which① austenitic stainless steel is digitally labeled with the 200 and 300 series.
② ferrite and martensitic stainless steel are represented by a 400 series of numbers.
For example, some of the more common austenitic stainless steels are marked with 201, 304, 316, and 310.
③ ferrite stainless steel is labeled with 430 and 446, martensite stainless steel is marked with 410, 420 and 440C, Duplex (Austenite-ferrite).
④ stainless steel, precipitated hardened stainless steel and high alloys with a iron content of less than 50% are usually named after a patent name or trademark.