Study On Plasma Rare Earth Nitro- Carburizing Of 30CrMnSiA Steel

This paper deals with pulse plasma RE nitrocarburizing of 30CrMnSiA steel. The microstructure, phase structure and element profiles in nitrocarburized layer were investigated using OM,XRD and EDS analysis. Microhardness test and friction wear test had been adopted to characterize the microhardness profile and wear resistance of the nitrocarburized layer. Experimental results indicate that the surface hardness of this steel has been increased significantly, the microhardness profile of gradient distribution in nitrocarburized layer has been obtained and the wear resistance has been improved by RE nitrocarburizing.Results form OM observation show that the nitrocarburized layer of 30CrMnSiA steel was composed of compound layer and diffusion layer. The increase of the layer depth and the weight gain per unit surface with nitrocarburized time conform to the parabolic law. The layer depth increases with enhancing nitrocarburizing temperature, while decreases with incremental pressure in the chamber.XRD analysis results reveal that phase structures of surface layer of 30CrMnSiA steel were constituted mainly of phasesγ'-Fe4N,ε-Fe3N,α'-Fe and a little of Fe3O4. The quantity ofγ'-Fe4N in surface layer is firstly increased and then decreased with prolonging treatment time.EDS analysis indicate that the carbon concentration in the nitrocarburized layer reaches 10~12at.% and the nitrogen concentration is about 23at.% when the nitrocarburizing is conducted at 500°C for 4h in a mixed gas of N2:H2:RE reagent =0.1:0.3:0.05.The nitrogen concentration drops sharply at the distance 10μm from surface, which is corresponding to the compound layer. When exceeding this layer, nitrogen concentration changes gradually and presents the diffusion layer.By pulse plasma RE nitrocarburizing, the surface hardness of 30CrMnSiA steel can be increased remarkably and the hardness profile presents a gradual variety in the nitrocarburized layer. The surface hardness of 500°C nitrocarburized layer enhances with increasing treatment time and the hardness of surface layer is about 985 HV0.1 for 16h nitrocarburizing. The surface hardness is firstly increased and then decreased with increasing the treatment temperature.The wear resistance of 30CrMnSiA steel can be improved remarkably by pulse plasma nitrocarburizing. at 500°C with RE addition and the wear rate is lowest for the RE reagent flux 0.1L/min. The wear resistance of the nitrocarburized layer decreases slightly with increasing nitrocarburizing temperature.