Study On Grain Refinement Of Bearing Ring Surface By Ultrasonic Rolling Extrusion

Bearing is widely used in all kinds of mechanical basic parts products,known as "industrial joints".It occupies an important position in modern industry and manufacturing technology.Its surface performance is inseparable from the service of bearings for a long time,and it is also the guarantee of the reliability of the whole set of mechanical equipment.The performance of bearing surface is closely related to the change of micro-structure,the former is the macro-reaction of the latter.Based on the traditional rolling extrusion technology,the ultrasonic rolling extrusion technology is developed.It has many advantages,such as small friction,grain refinement,high efficiency,and so on.At the same time,it forms compressive stress on the bearing surface In this paper,bearing material is taken as the research object,and the effect of ultrasonic roller extrusion process on grain refinement of workpiece surface is studied by ultrasonic roller extrusion process.Based on the principle of ultrasonic rolling extrusion,the grain refinement mechanism of 42 CrMo steel with BCC structure with high stacking fault energy was analyzed based on dislocation theory.After corrosion in 4% nitric acid alcohol solution,the change of microstructure was observed,and the original coarse microstructure became fine and compact.After corrosion with saturated picric acid,the surface grains became fine and uniform,and the grain size gradually increased from outside to inside,approaching the grain size of matrix,which laid a theoretical foundation for subsequent simulation and experiment.Based on the rule of metal plastic forming,the finite element simulation model of 42 CrMo bearing rings by ultrasonic rolling extrusion was established by Defrom-2D software.The grain changes of bearing rings under different processing parameters(frequency,spindle speed,static pressure and amplitude)were simulated,and the influence of different processing parameters on grain refinement of bearing rings was analyzed.Based on the experimental of ultrasonic rolling extrusion of 42 CrMo bearing material,the grain distributions at different locations were observed under electron microscopy after picric acid corrosion.The average grain size was calculated by Image Pro Plus image analysis software,and the influence of different parameters on grain size and depth of refined layer was analyzed.The results show that the grain size of workpiece surface increases with the increase of layer depth,decreases first and then increases gradually with the increase of rotational speed and amplitude,decreases with the increase of static pressure and increases with the increase of feed.This is basically consistent with the simulation results of different parameters on the impact of grain size.The surface properties of the workpiece were measured by microhardness tester,roughness tester and X-ray stress tester respectively.It was found that the surface roughness,microhardness and residual stress of the processed bearing rings changed significantly,which proved that the ultrasonic rolling extrusion process can effectively improve the performance of the bearing surface.