Scanning Electron Beam Surface Strengthening Effect And Its Mechanism On Column-faced 45 Steel

45 steel has good plasticity and toughness,easy to cut and other advantages and widely used,45 steel materials in practice,the work surface not only has a flat surface,there are different shapes of the surface such as columnar surface,conical surface,spherical surface,etc.The surface is often affected by the shape of the surface and the working environment,and defects such as wear,rust and cracks occur on the surface.The electron beam surface strengthening technology has a low deformation and high energy utilization rate for the workpiece.Scanning electron beam is used to achieve surface strengthening of columnar 45steel and improve its comprehensive surface properties.In this study,the mathematical and theoretical model of the temperature field of the scanning electron beam surface strengthening process of column-faced 45 steel was established based on the heat transfer theory,and the temperature field distribution law was obtained by using finite element simulation software.Further,the distribution of microstructure and mechanical properties of 45 steel with column surface was investigated by electron beam experiments.The effects of curvature of the column surface,electron beam current,electron gun travel speed and scanning ring outer diameter on the microstructure and surface mechanical properties were discussed.The strengthening effect and mechanism of electron beam were investigated.The results of the study are as follows.（1）the electron beam scanning ring can instantly heat up the surface of the specimen to reach the melting point and achieve secondary heating.As the scanning ring moves forward,the column surface temperature rises and cools rapidly,with the temperature peak exceeding the phase transition temperature.The temperature increases rapidly in the initial stage of electron beam strengthening;the temperature is more stable in the middle stage;and the temperature increases again in the closing stage.（2）After electron beam strengthening,the workpiece cross-section can be separated into three regions:the molten layer,the heat-affected zone and the substrate.The microhardness of curvature 1/20 tends to increase and then decrease in the depth direction,and the highest hardness is at the depth of about 50μm,with a value of 688.26 HV_0.1;the highest hardness in the circumferential direction is at the edge of the scanning ring,with a value of about 868 HV_0.1.（3）Curvature in the range of 1/25 to 1/10,with the increase of the curvature of the column surface,the martensite grain size of the melt solidification layer tends to decrease first and then increase;the modification depth increases nonlinearly,and the maximum modification depth is about 814μm at the curvature of 1/10.the wear amount tends to decrease and then increase with the increase of curvature,and the wear amount is the lowest at the curvature of 1/20,which is 0.5mg;the roughness increases non-linearly as curvature increases.（4）Within the beam current range of 11m A～13m A,as the beam current increases,the modification depth progressively increases,the martensite grains become more and more large,the microhardness first increases and then decreases.the roughness first increases and later decreases;the amount of wear first increases and later decreases.When the current is12 m A,the highest value of microhardness is 688.26 HV_0.1,about 3.13 times that of the matrix,and the amount of wear decreased from 2.7 mg to 0.5 mg.（5）In the range of electron gun moving speed 60 mm/min～120 mm/min,the depth of the modified layer is reduced gradually with the increase of the moving speed;the martensite grains became finer;the microhardness increases non-linearly as speed increases;the roughness decreases and then increases,and the roughness of the workpiece decreases from2.887μm to 1.047μm at the speed of 90mm/min;the wear amount decreased and then increased.（6）Within the scan diameter range of 8 mm to 10 mm,as the diameter increases,the depth of modification gradually decreases,and the deepest depth of modification is about1268μm at a diameter 8mm;the martensite grains of melt layer gradually become finer with the increase of scanning ring diameter;the microhardness of surface shows a non-linear decreasing trend;the roughness goes down;wear first decreases and then increases.