Effect Of Ultrasonic Rolling On The Surface Integrity And Corrosion Properties Of GCr15 Before And After Quenching

As one of the most commonly used bearing steels,GCr15 bearing steel has good comprehensive mechanical properties and is widely used in the fields of precision machine tool spindles,internal combustion engines and mining machinery.Due to the special working environment of GCr15 bearing steel,the parts will work under harsh conditions such as alternating load,high speed and corrosion for a long time,which is a very serious test for the life,reliability and corrosion resistance of the parts.Therefore,higher requirements are put forward for the performance of GCr15 bearing steel.The traditionally strengthened GCr15 has been unable to meet the current stringent performance requirements,and the ultrasonic surface strengthening technology,as an emerging surface strengthening technology,has the incomparable advantages of the traditional surface strengthening treatment,and has broad application prospects.This topic takes the combination of ultrasonic strengthening treatment and heat treatment as the breakthrough point,takes the ultrasonic simulation as the auxiliary,and combines the changes of ultrasonic processing parameters to study the influence law and influence mechanism of ultrasonic rolling on the surface integrity of GCr15 bearing steel.Scanning electron microscope,material surface three-dimensional texture and topography acquisition system,and metallographic microscope were used to explore the influence mechanism of microstructure and the three-dimensional topography of GCr15 after ultrasonic rolling.The results show that due to the staggered distribution of martensite,the existence of microcracks in martensite,and the irregular distribution of bainite and polygonal austenite grains the quenched specimen more prone to dislocation and slip,and the grain refinement effect is better than unquenched specimens.The unquenched specimen has a thicker refinement layer,which has an obvious rheological structure due to the large plastic deformation.Vickers microhardness tester,small surface roughness measuring instrument were used to analyze the effect of different ultrasonic rolling processing parameters and heat treatment on the surface hardness and surface roughness of GCr15.When the static load and rolling times are small,ultrasonic rolling has better peak-shaving and valley-filling effect on the surface of the quenched specimen,resulting in the roughness of the quenched specimen being smaller than that of the unquenched specimen.When the static load and rolling times are large,the roughness of the quenched specimen is larger than that of the unquenched specimen.Due to the high hardness and poor plasticity of the quenched specimen,the plastic deformation caused by the subsequent impact cannot fill the cavities generated by the previous impact,thus forming bulges and grooves,increasing the surface roughness.The residual stress distribution in the surface and depth directions of GCr15 under different ultrasonic machining parameters and heat treatment conditions was analyzed by ABAQUS simulation software,residual stress tester and X-ray diffractometer.The detection results of the residual stress on the surface of the blind hole method were compared with the simulation results and the stress analysis results by XRD to ensure and verify the accuracy of the simulation results and the scientificity of the inference analysis of the results.The results show that under small static load or few rolling times,the initial residual compressive stress of the quenched specimen is larger than that of the unquenched specimen due to the large plastic deformation.With the increase of static load and rolling times,the residual compressive stress of the unquenched specimen caused by large plastic deformation is larger and deeper than that of the quenched specimen caused by heat treatment and plastic deformation.The hardness of the unquenched specimen is much lower than that of the quenched specimen which is due to the better grain refinement effect of the quenched specimen.The three-electrode electrochemical workstation was used to analyze the influence of different ultrasonic rolling parameters and heat treatment on the corrosion resistance of GCr15.Studies have shown that ultrasonic rolling can improve the surface integrity and corrosion resistance of GCr15.The corrosion resistance of the quenched specimen is better than that of the unquenched specimen.The optimal process is ultrasonic rolling of quenched GCr15 steel with small static load and fewer rolling times,1000 N and 3 times,respectively.