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.
Ferrous metallurgy
Steel (with a carbon content between pig iron and wrought iron) was first produced in antiquity as an alloy. Its process of production, Wootz steel, was exported before the 4th century BC from India to ancient China, Africa, the Middle East and Europe. Archaeological evidence of cast iron appears in 5th-century BC China. New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century. During the Industrial Revolution, new methods of producing bar iron by substituting coke for charcoal were devised and these were later applied to produce steel, creating a new era of greatly increased use of iron and steel that some contemporaries described as a new Iron Age. In the late 1850s, Henry Bessemer invented a new steelmaking process, that involved blowing air through molten pig iron to burn off carbon, and so to produce mild steel. This and other 19th-century and later steel making processes have displaced wrought iron. Today, wrought iron is no longer produced on a commercial scale, having been displaced by the functionally equivalent mild or low carbon steel.