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.
Equivalent carbon content
For cast iron the equivalent carbon content (CE) concept is used to understand how alloying elements will affect the heat treatment and casting behavior. It is used as a predictor of strength in cast irons because it gives an approximate balance of austenite and graphite in final structure. The following formulas are used to determine the CE in cast irons: