Steel

Steel is an alloy primarily made of iron, with a carbon content between 0.02 % and 1.7 % by weight, depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are also used. Carbon and other elements act as a hardening agent, preventing dislocations in the iron atom crystal lattice from sliding past one another. Varying the amount of alloying elements and their distribution in the steel controls qualities such as the hardness, elasticity, ductility, and tensile strength of the resulting steel. Steel with increased carbon content can be made harder and stronger than iron, but is also more brittle. The maximum solubility of carbon in iron is 1.7 % by weight, occurring at 1130 °C; higher concentrations of carbon or lower temperatures will produce cementite which will reduce the material's strength. Alloys with higher carbon content than this are known as cast iron because of their lower melting point. Steel is also to be distinguished from wrought iron with little or no carbon, usually less than 0.035 %. It is common today to talk about 'the iron and steel industry' as if it were a single thing; it is today, but historically they were separate products.