Why are some elements added to alloys instead of used pure?

Pure metals are often too soft, too reactive, or not strong enough for practical applications. By adding elements such as carbon to iron to make steel, or chromium and nickel to make stainless steel, manufacturers can tailor mechanical and chemical properties. The added atoms disrupt the regular metallic lattice and can block deformation or improve resistance to corrosion. Alloy design is one of the most important ideas in materials chemistry and engineering.