Cast iron
Cast iron is made from pig iron, which is the product of smelting iron ore in a blast furnace. Cast iron can be made directly from the molten pig iron or by re-melting pig iron, often along with substantial quantities of iron, steel, limestone, carbon (coke) and taking various steps to remove undesirable contaminants. Phosphorus and sulfur may be burnt out of the molten iron, but this also burns out the carbon, which must be replaced. Depending on the application, carbon and silicon content are adjusted to the desired levels, which may be anywhere from 2–3.5% and 1–3%, respectively. If desired, other elements are then added to the melt before the final form is produced by casting.
William Kelly (inventor)
Before the technique of injecting air into molten iron was re-discovered by Kelly and by Bessemer, iron was available as cast iron, a strong but brittle metal made in a blast furnace by treating iron ore with coke derived from coal, and wrought iron, a more malleable and flexible metal made by heating iron ore in a low oxygen environment in a bloomery heated by charcoal and producing "blooms", which were 100 to 200 pound lumps of very low carbon iron mixed with slag. The blooms then had to be worked repeatedly by hammering with a helve hammer or later a steam hammer and folding it to work out the slag. This could in turn be converted to steel by heating it for prolonged periods sealed in stone boxes with charcoal, to add back carbon. The resulting steel could then be formed into larger shapes by heating it to welding temperature and hammering it together into a mass. Other laborious and expensive methods made small amounts of steel from special ores.