Stainless steel, a metal primarily is used as a heat resisting or corrosion resisting material. Listed below are all 4 groups of stainless steels: austenitic, ferritic, martensitic, and precipitation hardened (PH). These include the 200 Series, 300 series, 400 series, 500 series, and PH Grades. " Listed below are all 4 groups of stainless steels: austenitic, ferritic, martensitic, and precipitation hardened (PH). These include the 200 Series, 300 series, 400 series, 500 series, and PH Grades.