Effect Of Shot Peening And Ion Implantation On Microstructure And Properties Of 8Cr4Mo4V Steel

8Cr4Mo4V steel is widely used in aerospace engine bearings.In order to improve its performance,especially wear resistance and fatigue performance,the surface strengthening of 8Cr4Mo4 V steel is achieved by shot peening and ion implantation.In this paper,the shot peening strength curves of different shot peening pressure and shot peening time were measured by almen test piece.The effects of different shot peening strength on the microstructure,dislocation density,stress gradient and friction and wear performance of 8Cr4Mo4 V steel were studied.The effects of composite strengthening on microstructure,stress gradient,nanohardness and wear resistance of 8Cr4Mo4 V steel were also studied.XRD analysis showed that the phase structure of 8Cr4Mo4 V steel after shot peening did not change,but the diffraction peak shifted to the left,broadened,and the strength decreased.It indicated that three internal stresses were caused after 8Cr4Mo4 V steel shot peening.The dislocation density was calculated by the WH method.The dislocation density of 8Cr4Mo4 V steel after shot peening increases first and then decreases with the depth of the sample,and its trend is the same as that of the residual stress curve.With the increase of shot peening strength,the compressive stress value of each point and the total depth of compressive stress of 8Cr4Mo4 V steel increase.Since the shot peening causes work hardening,the microhardness increases as the shot peening strength increases.After the different shot peening strength of 8Cr4Mo4 V steel,the wear resistance is improved and The coefficient of friction is reduced from the original 0.8 to 0.6.The wear scar width is optimally reduced by 30.3% compared with the original sample.The composite strengthening of 8Cr4Mo4 V steel by shot peening and ion implantation increased with the increase of shot peening strength,and the nitrogen concentration and depth of the injection layer increased after ion implantation of 8Cr4Mo4 V steel.According to GXRD analysis,after the composite strengthening treatment of 8Cr4Mo4 V steel,carbides and nitrides are precipitated and nitrogen ions are implanted into the matrix and diffused into the carbide.After 8Cr4Mo4 V steel composite strengthening,the nano hardness increased to 16.6GPa.Compared with the original sample,the nano hardness increased by 55.1%.Compared with the direct ion implantation of 8Cr4Mo4 V steel,the nano hardness increased by 18.6%.The wear resistance of the composite treatment is further improved.The contact coefficient is 1.20 GPa,and the friction coefficient can be reduced to 0.5.Compared with the original sample,the wear scar width is optimally reduced by 62.6%.As the contact stress increases,the wear resistance of the 8Cr4Mo4 V steel decreases.In the ion implantation process,the residual stress gradient is determined by the increase of compressive stress caused by nitrogen ion implantation lattice distortion and the stress release caused by high temperature.