Iron Castings: Essentially an alloy of iron, carbon (2-4%) and silicon in which the carbon is present in excess of the amount which can be retained in solid solution in austenite at the eutectic temperature. When cast iron contains a specially added element or elements in amounts sufficient to produce a measurable modification of the physical properties of the section under consideration, it is called alloy cast iron. Silicon, manganese, sulfur, and phosphorus, as normally obtained from raw materials, are not considered alloy addition.