A Steel mill or steelworks is an industrial plant where steel is manufactured. Steel is an alloy of carbon and iron. Usually steel is produced in two stages: First, iron ore is reduced (or smelted) with coke and limestone. This is done in a blast furnace, and the result is pig iron. The part that is not used for pig iron is carried on as "molten iron". Impurities are removed, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required. Steel mills then turn molten steel into blooms, ingots, slabs and sheet through casting, hot rolling and cold rolling.