Numerical Simulation And Experimental Study On Electron Beam Surface Hardening Of 35CrMo Steel

35CrMo steel has high strength,good hardenability and toughness.It is often used to manufacture various parts of large mechanical equipment and widely used in manufacturing industry.However,the hardness and wear resistance of 35CrMo steel are relatively low,which can not fully meet the requirements of special working conditions and service life.Compared with conventional heat treatment,electron beam surface quenching technology developed rapidly in recent years has the advantages of high energy utilization rate and high machining accuracy,which can significantly improve the properties of material surface.In this paper,35CrMo steel as the research object,based on the theory of heat transfer and finite element method,the mathematical physical model of 35CrMo steel electron beam surface quenching was established by ANSYS finite element analysis software,and the distribution law of temperature field and its changes under different parameters were studied.Combined with the solution results of temperature field,the stress field is simulated by coupling method,and the distribution law of residual stress and the main factors affecting the residual stress are explored.According to the simulation results,electron beam surface quenching experiment was carried out,and the surface morphology,microstructure and surface properties of the specimen were observed,and compared with the simulation results.The simulation and experimental results show that the electron beam surface quenching is a process of fast cooling and fast heating,and the temperature variation trend of each point in the scanning area is basically consistent.When the beam current,scanning speed and beam spot diameter are 23m A,1000mm/min and 6mm respectively,the simulation results are ideal.When the experimental parameters are used for simulation,the heating temperature is stable at about 1305℃,and the maximum surface cooling rate can reach 0.9×10⁴℃/s.Surface peak temperature and temperature gradient are positively correlated with electron beam current,but negatively correlated with scanning speed and beam spot diameter.After cooling,the residual tensile stress and compressive stress both satisfyσ_SX>σ_SZ>σ_SY,and the Von Mises equivalent residual stress increases with the position closer to the center of electron beam spot,and the maximum value is 572Mpa,which accords with the fourth strength theory.Cooling rate is an important factor affecting the distribution and value of residual stress.After surface quenching by electron beam,the cross-section of 35CrMo steel sample can be divided into three regions:hardened layer,transition layer and matrix.The grains of hardened layer and transition layer have been refined to varying degrees,and the average microhardness of 35CrMo steel sample is730.5HV and 522.9HV,respectively,which are obviously higher than that of matrix.The frictional and wear weight loss of the specimens before and after electron beam surface quenching is 1.1mg and 0.3mg,severally,indicating that the wear resistance of the specimens after electron beam surface quenching has been greatly improved.The influence of electron beam process parameters on the hardening layer is consistent with that on the temperature field,which verifies the correctness and rationality of the numerical simulation.