The technological requirement is to finish quenching and tempering after completing the mold machining, so that the mould can achieve better comprehensive mechanical properties. One is 45, 55 and other high quality carbon steel, suitable for simple shape or low accuracy, long service life mold. SM45, SM55 and other plastic mould steels (YB/T094 - 1997, YB/T107 - 1997, YB/T129 - 1997) can be selected. This steel has good purity and stable mechanical properties. The other is alloy steel, which can be carbonitriding after quenching and tempering to further improve wear resistance and corrosion resistance. Among them: 40 CrMo has good low temperature toughness and low notch sensitivity, which is suitable for making medium die. 42 CrMo is a high strength steel with high fatigue limit and low temperature toughness. It is suitable for manufacturing large and medium-sized plastic moulds which require certain strength and toughness. 38 CrMoA1 is a typical carburizing steel. After quenching and nitriding, it has high surface hardness (greater than 850HV) and has a certain corrosion resistance. It is suitable for PVC, PC plastic mold. In addition, 5 CrNiMo, 5 CrMnMo and other hot work die steels are mainly used in plastic moulds, such as thermosetting plastic moulds, with high temperature and high wear resistance.