Steel is an alloy of iron and carbon and other elements. Because of its high tensile strength and low cost, it is a major component used in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons.

Iron is the base metal of steel. Iron is able to take on two crystalline forms (allotropic forms), body-centered cubic (BCC) and face-centered cubic (FCC), depending on its temperature. In the body-centered cubic arrangement, there is an iron atom in the center of each cube, and in the face-centered cubic, there is one at the center of each of the six faces of the cube.