| 30CrMo steel is commonly used in the manufacture of mechanical shafts,gears and valve workpieces due to its high strength and toughness.The workpieces are subjected to high speed impact and intense friction in the actual working condition,which easily lead to scratches and wear loss on the surface of the workpieces,so it is necessary to reinforce the surface performance of the workpieces.Electron beam surface polishing can reduce the surface roughness and enhance the surface properties,which is an effective method to realize the reinforcement of the surface properties of metal workpieces,and its process parameters have a dramatic influence on the surface properties of 30 CrMo steel workpieces.The temperature field model of scanning electron beam surface polishing treatment of30 CrMo steel was established in this paper,the temperature distribution law of sample surface and depth direction was investigated,and the impacts of beam current and electron gun moving speed on the temperature variation of surface and depth were studied.The ranges of process parameters were determined from the simulated temperature variations,the influences of beam current and electron gun moving speed on the microstructure and surface properties of the samples were evaluated,and the optimal process parameters are obtained.Eventually,the variations of microstructure and surface properties of single and double 30 CrMo steel after surface polishing were compared under the influence of optimal parameters,in expectation of further enhancement of 30 CrMo steel surface properties.The results showed that:(1)the maximum temperature of the sample surface gradually increased and reached the maximum at the closing end,and the temperature change curve showed two temperature peaks with height difference.The surface temperature grew with rising beam current,and the region of meeting the phase transition temperature in the depth direction increased.As the speed of electron gun movement increased,the heat transfer in the depth direction decreased and the temperature gradually dropped.(2)The ranges of process parameters were determined from the simulated temperature variations,the microstructure of the melted layer was needle and slate mixed martensite,the heat affected zone composed of complete quenching zone,partial phase transformation zone and transition zone.The martensite grains in the melted layer grew with the rise in beam current,and the grains were refined with increasing electron gun travel speed.Microstructure phase change impacts surface properties transformation.With the increase of beam current,the surface roughness of 30 CrMo steel reduced and then increased,the microhardness gradually increased,and surface wear resistance increased and then declined.When the electron gun movement speed increased,the surface roughness and wear resistance of the sample dropped and then rose,and the microhardness progressively decreased.When the beam current is9 m A and the electron gun moving speed is 4mm/s,the surface roughness was reduced to the lowest value of 0.951μm,which was 57.03% lower compared to the original sample.The surface martensite size was refined,the surface microhardness was increased by 1.44 times,the wear was decreased by 50%.(3)Under the application of optimal parameters,the microstructure of the remelted layer of 30 CrMo steel was slaty,needle and cryptocrystalline martensite after double polishing treatment.The surface roughness of 30 CrMo steel was not significantly changed.As the depth direction grew,the microhardness of the cross-section increased and then decreased,and the microhardness of the cross-section of the sample after double polishing was higher than that of the single polishing.Compared with the surface hardness and wear of the sample after single polishing,the surface microhardness was increased by 21.45% and the surface wear was significantly reduced by 33.33% after double polishing. |
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