Austenitic stainless steel is a specific type of stainless steel alloy. These stainless steels possess austenite (gamma-phase iron) as their primary crystalline structure. There are two subgroups of austenitic stainless steel. 300 series stainless steels achieve their austenitic structure primarily by a nickel addition while 200 series stainless steels substitute manganese and nitrogen for nickel, though there is still a small nickel content.