Microstructure And Properties Of Hybrid Modified Layer Of 42MnCr52 Steel By Ultrasonic Surface Rolling And Plasma Sulfonitrocarburizing

42MnCr52 steel is often widely used in the manufacture of engine cylinder liners due to its good comprehensive performance and low price.In view of the fact that the engine cylinder liner is a frictional moving part,it is prone to scratches and wear failures during use.In addition,because some engine cylinder liners require water cooling,they are also prone to corrosion failure.Therefore,it is necessary to take into account not only the friction and wear performance but also its corrosion performance.In this paper,by comprehensively analyzing the metallographic structure,phase composition,microhardness,chemical elements and microstructure,the effect mechanism of Ultrasonic Surface Rolling Processing(USRP)on the process of Plasma Sulfonitrocarburizing(PSNC)is studied.According to the service conditions of the materials,the friction and wear test and corrosion test were performed on PSNC specimens and USRP+PSNC specimens to study their friction and wear properties and corrosion properties.The results show that the surface of material pre-treated by ultrasonic surface rolling formed a gradient nano-layer with a thickness of about 80 ?m.During ultrasonic surface rolling processing,the grain refinement occurred in different degrees along the direction perpendicular to the surface and a large number of non-equilibrium defects occurred under the action of cyclic alternating load.High-density non-equilibrium defects can increase the surface activity energy and enhance the surface's adsorption of active atoms,and the large number of grain boundaries can also serve as fast atomic diffusion channels.These characteristics have obviously promoted plasma sulfonitrocarburizing.Compared with PSNC specimen,the sulfide layer of USRP+PSNC specimen is more dense and uniform and contains more FeS phases;the average thickness of nitrocarburized layer of USRP+PSNC specimen was increased by 30%,and the uniformity of its thickness has also been improved to some extent.The friction and wear test results show that the friction coefficient of USRP+PSNC specimen was mostly lower than that of the PSNC specimen;from the perspective of wear volume,the wear volume of USRP+PSNC specimen has always been lower than that of PSNC specimen,that is,the friction and wear performance of USRP+PSNC specimen is better than that of the PSNC specimen.In the process of dry friction and oil-lubricated friction and wear,the main difference between the two different specimens wear mechanisms is that PSNC specimen is more prone to fatigue wear and abrasive wear than USRP+PSNC specimen.It was found from the polarization curves and electrochemical impedance spectroscopy measured by electrochemical experiments that the corrosion tendency and corrosion rate of USRP+PSNC specimens were lower than PSNC specimens.After immersion corrosion experiments,it was found that the corrosion mechanism of two specimens were significantly different.USRP+PSNC specimens were mainly uniformly corroded,while PSNC specimens had more local corrosion.Based on the above analysis results,USRP+PSNC specimens has better corrosion resistance.