Research On Surface Rolling Strengthening For Shaft Parts Made Of Cr12

With the development of society and the progress of science and technology,the requirements for the performance,reliability and service life of mechanical equipment are becoming higher and higher.Therefore,how to improve the mechanical properties of parts in mechanical equipment,and then improve the performance of the whole machine,has become an important topic in the field of mechanical engineering.Surface rolling strengthening is a kind of processing technology which can realize surface strengthening of parts by means of mechanical processing.It can produce residual compressive stress on the surface of parts,reduce surface roughness,improve surface hardness,improve wear resistance and corrosion resistance,and effectively prolong the service life of parts.In this paper,a surface rolling strengthening device for axle parts based on C616 lathe is developed independently,which is installed on the large bracket of lathe,including hydraulic system and mechanical part.In the working process,the hydraulic system provides rolling pressure,and the lathe provides the mutual movement between the roller and the specimen.The device is symmetrical structure,the radial resultant force of two symmetrical rollers acting on the specimen is zero,which avoids the influence of rolling pressure on the spindle of the machine tool.The effect of rolling parameters on surface residual stress,microhardness,surface roughness and wear resistance of Cr12 specimens was studied by surface rolling strengthening test.After rolling,the surface residual stress of Cr12 specimens changes from the residual tensile stress of 52 MPa to the residual compressive stress of-47 MPa to-216 MPa.With the increase of contact stress and rolling passes,the residual compressive stress first increases and then keeps stable.With the increase of depth,the residual compressive stress first increases and then decreases,and the residual compressive stress layer is more than 0.2 mm.After rolling,the surface microhardness of the specimens is obviously improved,the maximum surface microhardness reaches 360 HV_0.2,and the maximum increase is more than 30%.With the increase of contact stress,the microhardness increases first and then keeps stable.Surface rolling strengthening can effectively change the surface morphology of specimens,and the surface roughness can be reduced by 25%-67%.In the rolling parameters mentioned in this paper,with the increase of contact stress and rolling passes,the surface roughness shows a decreasing trend.Friction and wear tests show that with the increase of contact stress and rolling passes,the wear rate decreases gradually,that is,the wear resistance improves continuously.The micro-structure of the surface of the specimens after rolling was analyzed and studied.The intrinsic relationship between rolling parameters and residual stress,surface roughness,surface hardness and wear resistance was revealed.The phenomenon of grain elongation and carbide crushing appeared on the surface of the specimens after rolling,which indicated that under the action of roller,the morphology and grain size of the surface microstructures of Cr12specimens changed and grain refinement occurred,which resulted in the changes of residual stress,microhardness and wear resistance of the specimens and the decrease of surface roughness..The rolling strengthening model of Cr12 is established by Abaqus/Explicit to predict the distribution of residual stress after rolling,and the regression equation of residual stress about contact stress and rolling pass is established by simulation results,which can effectively predict residual stress.At the same time,the simulation results show that the residual compressive stress layer first increases and then decreases on the surface of the specimen after rolling.The maximum residual compressive stress occurs at about 0.1mm away from the surface,and the thickness of the residual compressive stress layer is about 0.3mm-0.5mm.