Stainless steel is an alloy containing at least 11.5 percent chromium and at least 50 percent iron. Additional components are nickel, carbon, manganese, silicon and nitrogen. The amount of each component is varied according to the desired use.
Over 150 grades of stainless steel exist and are classed according to the percentage of chromium they contain. Austenitic steels contain at least 16 percent chromium and are highly resistant to corrosion. Ferritic steels contain 10.5 to 27 percent chromium and cannot be work-hardened. Martensitic steels contain 12 to 14 percent chromium and are magnetic. Duplex steels are a mixture of austenite and ferrite and can be double the strength of austenitic stainless steel.