A steel mill or steelworks is an industrial plant for the manufacture of steel.Steel mill can refer to the steel works making rolled products from iron ore, but it also designs, more precisely the plant where steel semi-finished casting products (blooms, ingots, slabs, billets) are made, from molten pig iron or from scraps.Since the invention of the Bessemer process, steel mills have replaced ironworks, based on puddling or fining methods.