The American Iron and Steel Institute uses three-digit numbers to identify various standard grades of malleable stainless steel. Thereinto:
(1) Austenitic stainless steels are numbered with 200 and 300 series.
(2) Ferritic and martensitic stainless steels are represented by numbers in the 400 series. For example, some of the more common austenitic stainless steels are marked 201, 304, 316 and 310.
(3) Ferritic stainless steel is marked with 430 and 446, martensitic stainless steel is marked with 410, 420 and 440C, duplex (austenitic-ferritic).
(4) Stainless steel, precipitation hardening stainless steel and high alloys with less than 50% iron content are usually named by patent or trademark.
