Numerical Simulation And Experimental Research On Surface Modification Of 40cr High-current Pulsed Electron Beam

In this paper,the process of specimens irradiated by intense pulsed electron beam is studied by finite element simulation combined with experiment.The finite element model of temperature field,stress field and crater eruption is established by using 40 Cr as research material.The model was solved by standard/CAE of ABAQUS.The surface and cross-section of the sample were observed by scanning electron microscopy(SEM)and metallographic microscope(OM).The phenomena of surface modification,melting pit and thermal stress were analyzed and explained by comparison of simulation and experiment.(1)Simulated analysis of temperature fieldThe heat transfer method is used to solve the model.The thermal conductivity,specific heat,temperature,thermal radiation and latent heat of phase change are taken into account.Then the temperature distribution of 40 Cr in quenched and tempered state and annealed state is simulated,and the temperature field distribution under different acceleration voltage and radiation times is obtained.Through the comparative analysis of the results,taking quenched and tempered 40 Cr as the research object,the depth of melting layer(0-4 um)increases linearly within the acceleration voltage(21 kV-30 kV)when the irradiation times(25 times)are quantified.When the acceleration voltage(27kV)is fixed,the depth of the melting layer increases obviously at the first irradiation.When the number of irradiation reaches a certain number(5-10 times),the depth of the melting layer is no longer affected by the number of irradiation.Taking annealed 40 Cr as the research object,the results reveal that the temperature distribution in pearlite region is more "convergent" and the melting layer is thicker than that in cementite.(2)Stress field simulation analysisTemp-Disp analysis step with direct thermo-mechanical coupling is used to solve the problem.The elastic modulus,Young's modulus and temperature-related parameters are set.The stress distribution shows that the thermal pressure of the subsurface layer is greater than that of the surface and the center during the heating process.The principal stress reveals that the expansion of the surface layer is constrained by compressive stress and the core receives tensile stress.By testing and simulating the residual stress,the tensile stress in the surface layer and the compressive stress in the subsurface layer are obtained.Stress-induced dislocation,lattice distortion and fine-grained structure will increase the surface hardness of the material.The hardness of the surface strengthened is higher than that of the matrix.However,the tensile stress of the surface layer will reduce the hardness,while the compressive stress of the sub-surface layer will increase the hardness,resulting in the hardness distribution along the depth direction descending first and then rising.(3)Molten pit simulation analysisA 40 Cr finite element model containing carbide particles was established.The experimental results show that the fine second phase particles produced by electron beam radiation can enhance the strength of the material,and the surface roughness of the material will increase due to the eruption of the molten pit.The simulation results show that the main reason for the formation of melting pits is that the difference of thermal physical parameters between carbide particles and matrix results in the uneven distribution of temperature inside the material.The thermal conductivity is less than that of the matrix,which leads to the accumulation of heat.In addition,the low melting point of itself causes the melting and eruption of carbide in the surface layer.Statistical analysis of molten pits with MATLAB shows that the relationship between process parameters and distribution of molten pits is as follows.With the increase of irradiation times and acceleration voltage,the number of molten pits per unit area decreases and the average size increases.