Study On Surface Polishing And Modification Of 42CrMo Steel By Scanning Electron Beam

42CrMo steel is a medium carbon modulated type of alloy structural steel,belonging to the category of ultra-high strength steel.Due to its excellent mechanical properties and machinability,it is widely used in important fields such as key component manufacturing.42 CrMo steel often uses traditional heat treatment processes such as quenching in traditional production and processing processes.During the heat treatment process,cracks are prone to occur due to reasons such as coarse microstructure and stress concentration,thereby affecting processing quality and efficiency.As an emerging surface heat treatment technology,continuous electron beam surface polishing and modification technology can replace traditional heat treatment processes to polish and strengthen the surface of 42 CrMo steel,avoiding problems such as thermal deformation.It can also improve surface quality and reduce processing costs while reducing surface roughness.In this paper,a finite element model of temperature field for 42 CrMo steel continuous scanning electron beam surface polishing and modification is established by using the Gaussian surface heat source,and the temperature distribution and thermal cycle curve in the whole process are analyzed;Based on the simulation results,a reasonable range of scanning process parameters was determined for orthogonal experiments.The optimal process parameters for electron beam scanning of 42 CrMo steel were determined based on the orthogonal experimental results,and the influence of electron beam process parameters on the material structure,properties,and polishing effect was discussed;On the basis of the optimal process parameters,study the influence of the number of co directional repeated scans on the polishing effect,overall morphology,microstructure,and mechanical properties.The results show that during the heating process,the surface temperature of the sample changes in three stages.The first stage steadily increases,and then reaches the second stage to maintain stability.In the third stage,it continues to rise to its peak with time.During the cooling process,the cooling rate first increases and then slows down until the sample temperature drops to room temperature.The thermal cycling curve along the scanning direction and the thermal cycling curve along the depth direction both have two peaks,and the latter peak is higher than the previous peak.The modified layer of 42 CrMo steel after scanning electron beam treatment is divided into three parts: melting zone,Heat-affected zone and matrix.The melting zone is mainly composed of lath and acicular martensite,and the Heat-affected zone is mainly composed of acicular,Flat noodles martensite,cementite,ferrite and pearlite;The surface roughness first increases and then decreases with the increase of scanning ring diameter,then increases and then decreases with the increase of beam current,and nonlinearly increases with the increase of electron gun movement speed;After optimal processing parameters,the surface roughness is 0.6411 μm.Compared to before treatment,it decreased by 80.0%,and the microhardness first decreased,then increased,and then slowly decreased as the distance from the surface increased.The maximum microhardness value appeared at a depth of 40 μ At the Heat-affected zone of m,the peak value is 754.7HV,which is 2.35 times of the matrix.The friction coefficient of the sample is about 0.7101,which is 32.4% lower than that before treatment.The modified layer of 42 CrMo steel after one,two,three and four times of repeated scanning treatment in the same direction has the same zoning,which is divided into three parts: the melting zone,the Heat-affected zone and the matrix.The microstructure of the melting zone is acicular martensite and lath martensite,and the microstructure of the Heat-affected zone is martensite,cementite,ferrite and pearlite;The surface microhardness first increases and then decreases with the increase of scanning times.The highest hardness is 885.1HV at 3 scanning times,which is 2.76 times the hardness of the matrix.The surface roughness first decreases and then increases with the increase of scanning times.The lowest surface roughness is 0.5431 at 3 scanning times μm.Compared to before treatment,it decreased by 83.0%.With the increase of scanning times,the weight loss after friction and wear of the sample first decreased and then increased.At 3 scanning times,the weight loss after friction and wear was the lowest,0.09 mg,which was 92.5% lower than before treatment.The friction coefficient also decreased from 1.050 to 0.2774,a decrease of 73.6%,and the wear resistance was significantly improved.