Cast iron is one of the oldest ferrous metals in commercial use. It is primarily composed of iron (Fe), carbon (C) and silicon (Si), but may also contain traces of sulfur (S), manganese (Mn) and phosphorus (P). It has a relatively high carbon content of 2% to 5%. It is typically brittle and nonmalleable (i.e. it cannot be bent, stretched or hammered into shape) and relatively weak in tension. Cast iron members tend to fracture with little prior deformation. Cast iron, however, has excellent compressive strength and is commonly used for structures that require this property. The composition of cast iron, the method of manufacture and heat treatments employed are critical in determining its final characteristics.
To achieve the best casting for a particular application consistent with the component’s requirements, it is necessary to have an understanding of the various types of cast iron. The general designation of cast iron is meaningless, except when distinguishing the part from a steel casting. Therefore, a more specific designation should be made. Cast irons can be divided into five groups, based on composition and metallurgical structure: