Cast iron generally refers to a multi-component iron carbon alloy with a C content of more than 2.0% (wt%, the same below). Generally, the C content of industrial cast iron is 2.5-3.5%. C mostly exists in the form of graphite in gray cast iron, and a small amount exists in the form of Fe3C. In addition to C, grey cast iron also contains 1-3% Si, Mn, P, s and other elements. C. Si, Mn, s and P are the five basic elements in cast iron. In addition, according to the service conditions and required properties of castings, cast iron also contains Ni, Cr, Mo, A1, Cu, Sb, V and other alloy elements.

The content of C in grey cast iron is high, and its matrix structure varies according to the cooling and solidification process. Generally, it can be divided into three categories: ferrite matrix grey cast iron, pearlite ferrite matrix grey cast iron and pearlite matrix grey cast iron.

According to the microstructure analysis of grey cast iron, the difference in classification is actually the content of different forms of C in cast iron. Its main types are compound carbon (Fe3C) and G (graphite). When Fe3C is 8%, it is pearlitic grey cast iron; When Fe3C is less than 0.8%, it belongs to pearlite ferrite grey cast iron; When C exists only in g state, it is a ferritic grey cast iron.