There is a certain corresponding relationship between hardness and tensile strength of gray cast iron. The empirical formula is: a, when O is 196N/m, the relative hardness of grey cast iron is mainly determined by raw material and melting process. The treatment process and the cooling rate of the casting are determined. Carbon, silicon and manganese are the elements that regulate the structure of cast iron, and sulfur is the element that should be restricted. At present, the chemical composition of cast iron is generally such as: WCU 2.7% ~ 3.6% WSI 1.0% ~ 2.3% WMnN 0.5% ~ 1.3% WS 0.15%.