Research On Surface Compound Reinforcement Technology Design And Performance Of Gear Steel 18Cr2Ni4WA

Carburized heat treatment is widely used to enhance the surface hardness,wear resistance,and meanwhile maintain good toughness in the central location.However,the traditional carburized is limited by higher carburized temperature and longer carburized cycle.The rare earth ion implantation technology can improve material properties by changing the physical and chemical properties of the surface and interface.Surface nanocrystallization technology can obtain nanocrystalline microstructure on the surface of various metal materials,and this technology can enhance carburized kinetics,and effectively achieve low temperature carburized.In this paper,surface nanocrystallization or ion implantation is used as a pretreatment method for vacuum carburizing of gear steel 18Cr2Ni4 W to promote vacuum carburizing process,finally,shot peening of carburized layer.The purpose is to improve the contact fatigue performance,bending fatigue performance and friction and wear properties of gear steel materials.The results show that:A layer of nanocrystalline modified layer is prepared on the surface of the substrate by supersonic particle bombardment technology.Nanocrystallization treatment is the best process.As the nanocrystallization time increases,the hardness of the surface of the substrate increases and the maximum is 48.3HRC,the thickness of the nano-layer increases,surface roughness increases first,then decreases and then stabilizes;the grain size of the nano-crystal modified layer decreases,and the microscopic strain and residual compressive stress increase,which does not change the phase structure of the original structure.The effective depth of ion implantation La is about 60 nm,and it exists in the substrate in the form of lanthanum oxide,which will not change the original tissue phase structure of the substrate.The average nano-hardness of the substrate surface will be improved and the friction coefficient will be reduced.The best results of the carburized layer at 920 °C without pretreatment.The surface structure after vacuum carburizing is martensite,carbide and retained austenite;the increase of carburizing temperature will lead to the martensite structure coarsening,the amount of retained austenite increases,the hardness decreases,and the friction and wear performance decreases,but the thickness increase.The microstructure of the two layers of pre-treatment auxiliary vacuum carburizing is martensite,carbide and retained austenite;pretreatment can improve the quality of the carburized layer,refine the grain,and the phase structure does not change.;surface rockwell hardness is significantly increased compared with the untreated,the retained austenite amount is significantly reduced;Significant increase,the calculated infiltration rate is 7.7%,9.6%;All of normal and 100°C temperature friction and wear performance,artificial seawater environment friction and wear performance compared with the untreated have been improved,nano-240 s and ion-implanted La are not much different in terms of the rate of infiltration or the improvement of the performance of the original carburized layer.Nano-240 s was used as pretreatment,920 °C vacuum carburization and shot peening were the final composite strengthening methods.To evaluate the contact fatigue,bending fatigue and friction wear performance of carburized layer.The contact fatigue failure form of the carburized layer is pitting or shallow spalling.The fatigue cracks can be seen in the section of the failure part,showing dendritic propagation.The macroscopic fracture morphology of flexural fatigue fracture has obvious beach pattern stripes,and the microcosmic morphology shows obvious dimples in the fatigue source area with carbide in the center,and there are obvious fatigue streaks in the crack growth zone.The coefficient of friction under oil lubrication conditions does not exceed 0.1;the calculated average wear rate is ?v = 0.24 ?m/h.Under assessment index stipulated in this article,on the surface of nanometer 240 ? after 240 s vacuum carburizing and shot peening specimens under specified standard of reliability for more than 95%..