Stainless steel, stainless-steel equipment [Credit: © Mark Yuill/Shutterstock.com] any one of a family of alloy steels usually containing 10 to 30 percent chromium. In conjunction with low carbon contents, chromium imparts remarkable resistance to corrosion and heat. Other elements such as nickel, molybdenum, titanium, aluminum, niobium, copper, nitrogen, sulfur, phosphorus, and selenium may be added to increase corrosion resistance to specific environments, enhance oxidation resistance, and impart special characteristics.
Most stainless steels are first melted in electric-arc or basic oxygen furnaces and subsequently refined in another steelmaking vessel, mainly to lower the carbon content. In the argon-oxygen decarburization process, a mixture of oxygen and argon gas is injected into the liquid steel. By varying the ratio of oxygen and argon, it is possible to remove carbon to controlled levels by oxidizing it to carbon monoxide without also oxidizing and losing expensive chromium. Thus, cheaper raw materials, such as high-carbon ferrochromium, may be used in the initial melting operation.
There are three major groups in the family of stainless steels: austenitic, ferritic, and martensitic. Austenitic steels, which contain 16 to 26 percent chromium and up to 35 percent nickel, usually have the highest corrosion resistance.