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.
Technological and industrial history of the United States
Although steel is an alloy of iron and a small amount of carbon, historically steel and iron-making were intended for different products given the high costs of steel over wrought iron. The main difficulty with making steel is that its higher melting point than pig or cast iron was not easily achievable in large-scale production until methods that introduced air or oxygen to oxidize the carbon in the molten pig iron were developed, allowing the direct conversion of molten pig iron to molten steel.