40Cr is a standard steel grade in China's GB specification, and 40Cr steel is one of the widely used steels in the machinery manufacturing industry. It exhibits excellent comprehensive mechanical properties after heat treatment, good low-temperature impact toughness, and low notch sensitivity. The steel has good hardenability, capable of being quenched through Φ28～60mm by water quenching and Φ15～40mm by oil quenching. Besides heat treatment, this steel is also suitable for cyaniding and high-frequency quenching processes. It has good machinability, with a relative machinability of 60% when the hardness is between 174～229HB. This steel is suitable for medium-sized plastic molds and shaft-type components.