Effects of rare earths addition on the microstructure, wear and corrosion resistances of plasma nitrided 30CrMnSiA steel

30CrMnSiA steel was plasma nitrided in an atmosphere of 50% N ₂+50% H ₂ at 460°C for 4h with and without rare earths addition, and the effects of rare earth elements on the microstructure and properties were investigated. The specimens nitrided with and without rare earths addition were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, microhardness tests, pin-on-disc tribometer and the anodic polarization method in a 3.5% NaCl solution. The results show that both nitrided layer with and without rare earths consist of a compound layer and a diffusion zone. The introduction of rare earths into the atmosphere can enhance the proportion of ε-Fe _2-3N phase in the surface layer and increase the surface layer hardness by 100HV _0.1. Both the wear and corrosion resistances of 30CrMnSiA steel were improved by plasma nitriding, i.e. the friction coefficient and the wear rate can be dramatically decreased. Moreover, the involvement of rare earths further decreases the average friction coefficient and the wear rate of specimens, and improves the corrosion resistance.