Stainless steel is an alloy of iron and carbon, containing at least 10.5% chromium and usually nickel, and may also contain other elements such as carbon, silicon, manganese, phosphorus, sulfur, molybdenum, titanium, niobium, and nitrogen to obtain the desired properties. The exact composition of stainless steel is a wide-ranging topic, with small changes in constituent metals potentially making significant adjustments in properties. The ratio of the metals that makeup the alloy determines which family the stainless steel grade belongs to, and there are five different families of stainless steel: austenitic, ferritic, austenitic-ferritic (duplex), martensitic, and precipitation-hardened. The corrosion resistance and mechanical properties of stainless steel can be further enhanced by adding other elements, such as nickel, molybdenum, titanium, niobium, and manganese.

In summary, the composition of stainless steel includes iron, carbon, at least 10.5% chromium, and usually nickel, along with other elements that can be added to enhance its properties.