Effects of QPQ Treatment on Microstructure and Properties of 20CrMn5 Gear

20CrMn5 gear was strengthened by QPQ process, and its microstructure, hardness, friction performance and fatigue performance were tested.The experimental results show that QPQ treatment can generate a carbon/nitrogen composite strengthening layer with a thickness of about 20 μm, and the average surface hardness is 702 HV0.3, which is 52.3% higher than that of the untreated gear surface.The core hardness is reduced to 250 HV0.3, and it has more excellent toughness.At the same time, the wear resistance and wear reduction of the treated gear are greatly improved, and it has excellent contact fatigue and bending fatigue performance.