40Cr steel, after quenching and tempering treatment, has good comprehensive mechanical properties, good low-temperature impact toughness, and low notch sensitivity. The hardenability of steel is good, it can be quenched to 28-60mm in water and 15-40mm in oil. This type of steel is suitable for cyanide and high-frequency quenching treatment in addition to quenching and tempering treatment. The cutting performance is good, with a relative machinability of 60% when the hardness is between 174-229HB. This steel is suitable for making medium-sized plastic molds.

42CrMo steel belongs to ultra-high strength steel, which has high strength and toughness, good hardenability, no obvious tempering brittleness, high fatigue limit and resistance to multiple impacts after quenching and tempering treatment, and good low-temperature impact toughness. 42CrMo steel is suitable for manufacturing large and medium-sized plastic molds that require certain strength and toughness.