Effect Of Laser Shock Peening On The Microstructure And Mechanical Properties Of 8Cr4Mo4V Steel

8Cr4Mo4V steel is a high-temperature alloy steel with comprehensive properties of high hardness,high strength and high fatigue life,which is widely used in the manufacture of aero-engine spindle bearings.With the continuous progress of aerospace technology,aerospace bearings need to withstand greater loads in service,and the severe working conditions have put forward higher requirements for the comprehensive mechanical properties of aerospace bearing steel.In order to improve the service life of 8Cr4Mo4 V steel,surface strengthening methods can be used,of which laser shock peening(LSP)flexibility,accuracy,efficiency,etc.compared to the traditional surface strengthening technology is higher,and the strengthening process is pollution-free,in line with the requirements of green environmental protection.Laser impact peening is a new type of surface peening technology,which uses the plasma shock wave pressure generated by the laser beam on the metal surface to produce dynamic plastic deformation,inducing a high level of residual compressive stress,thereby significantly improving the microhardness,wear resistance,fatigue resistance and other properties of the metal surface.The optimal laser parameters for strengthening 8Cr4Mo4 V steel were selected by the experimental method of controlled variables in this study.The samples of 8Cr4Mo4 V steel without laser shock peening treatment were compared with those strengthened with different parameters to analyze the effects of laser impact strengthening on the surfac e condition,hardness,residual stress,and fatigue properties of the samples,so as to further improve the comprehensive mechanical properties of 8Cr4Mo4 V and provide experimental data and theoretical basis for promoting its engineering applications.The study showed that the best strengthening effect was achieved when aluminum foil was used as the absorbing protective layer,the laser output energy was 8 J,the pulse width was 15 Ns,and the number of laser impacts was not greater than three.As the laser output energy gradually increases,the surface damage of the sample becomes more and more obvious,and the shape of the damage gradually changes from a crater to a long gully.8Cr4Mo4 V steel specimens surface hardness and hardness affected layer depth increases with the increase of laser output energy and laser impact times,and decreases with the increase of laser energy pulse width.When the laser impact strengthening output energy was 8 J,pulse width was 15 Ns,and the number of laser impacts was 3,the surface hardness of the specimens increased by 9.5% compared with the specimen without LSP treatment,and the strengthening depth was up to 700 μm.After laser impact strengthening,the residual compressive stress on the surface of 8Cr4Mo4 V steel was-866 MPa,and the fatigue limit was increased from 740 MPa to 1090 MPa,which was 47.3%.The improvement was 47.3%,the wear amount decreased by 93.1%,and the depth of wear marks was reduced by 84.18%.