Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition) . It is made by remelting pig iron, often along with substantial quantities of scrap iron and scrap steel, and taking various steps to remove undesirable contaminants such as phosphorus and sulfur. Carbon and silicon content are reduced to the desired levels, which may be anywhere from 2% to 3. 5% for carbon and 1% to 3% for silicon depending on the application. Other elements are then added to the melt before the final form is produced by casting.
Iron is most commonly melted in a small blast furnace known as a cupola (see blast furnace for more details) . After melting is complete, the molten iron is removed or ladled from the forehearth of the blast furnace. This process is thought to have been devised by the late 18th century ironmaster john wilkinson, whose innovative ideas revolutionized the field of metallurgy. Previously, iron was melted in an air furnace, which is a type of reverberatory furnace.