Research On The Simulation And Experiment Of The Scanning Electron Beam Surface Modification For The 40CrNiMoA Steel

40CrNiMoA alloy quenched and tempered steel has good overall performance and is widely used in the manufacture of high-load parts such as shafts.It is often necessary to perform surface treatment in work to improve its surface wear and insufficient hardness.Scanning electron beam surface treatment has gradually become an emerging force in the surface modification industry due to the advantages of high energy conversion rate,easy control of process parameters,and clean processing.In this paper,40 CrNiMoA steel is used as the research object,and the finite element software COMSOL Multiphysics is used to establish the mathematical model of the temperature field of the scanning electron beam surface modification.The distribution law of the temperature field at different times during the scanning process is explored.The temperature parameters of different scanning electron beam process parameters are discussed.Investigate the influence of the distribution law;perform tempering pretreatment on 40 CrNiMoA steel,use a scanning electron beam welding machine to conduct surface modification experiments on the pretreated sample,use laser confocal microscope,scanning electron microscope,X-ray diffractometer,Microhardness tester and material surface performance comprehensive tester study the changing law of the modified layer size,microstructure distribution and surface mechanical properties;finally explore the beam current and electron gun moving speed respectively on the material microstructure and surface mechanical properties Law of influence.The research results show that: scanning electron beam can rapidly raise the surface of the 40 CrNiMoA steel sample to above the melting point,so that the surface material reaches the molten state,and the temperature will suddenly rise during the scanning electron beam closing stage;scanning electron beam process parameters(beam current,The movement speed of the electron gun,and the scanning radius)have a significant effect on the simulation results of the temperature field.The peak surface temperature presents a law of nonlinear increase with the increase of the beam current,and a nonlinear decrease with the increase of the movement speed of the electron gun and the scan radius.the trend of.The 40 CrNiMoA steel has a beam current of 9m A,an electron gun moving speed of 5mm / s,and a scanning radius of4 mm.After scanning electron beam surface modification treatment,the cross-sectional structure of the modified layer is divided into two parts,a melting zone and a heat-affected zone.Martensitic structure with higher hardness appears in the area.The structure in the melting zone is coarser sheet martensite with a hardness of 669.2HV1,while the structure in the heat affected zone is a finer martensite with a hardness of 701.5HV1.;Below the modified layer is the matrix,the matrix region is composed of tempered sorbite,the hardness is only 336.3HV1,less than half of the hardness of the heat affected zone;the changes in beam current and moving speed on the surface modification layer profile of 40 CrNiMoA steel are studied The influence of size,microstructure and mechanical properties,the study found that the thickness of the surface modification layer increases nonlinearly with the increase of the beam current,and decreases nonlinearly with the increase of the moving speed of the electron gun;martensite in the heat affected zone The size gradually increases with the increase of the beam current,and decreases with the increase of the moving speed of the electron gun.When the beam current is increased to more than 10 m A or the moving speed of the electron gun is reduced to 3mm/s,a certain number of volcanic craters will be generated on the surface,resulting in defects in surface quality;the surface roughness first decreases slowly and then increases rapidly with the increase of the beam current The law is the smallest at 9m A,which is 0.889?m.With the increase of the moving speed,it shows a trend of rapid decrease and then increase,and the lowest at 5mm / s,it is 0.708?m;the wear resistance decreases first and then increases with the beam current.The law of increase also shows a trend of decreasing first and then increasing as the moving speed increases.