Research On Strengthening Mechanisms Of Shot Peening Combined With Ultrasonic Surface Rolling For Novel Gear Steel In High Power Density Gearbox

As the requirements for power density and service life of vehicles increase,the high-load operation of transmission gears makes it extremely prone to wear and fatigue damage,which seriously reduces the reliability and stability of vehicle operation.The SEM,TEM and EBSD are used to analyze the microscopic characteristics of the 17Cr2Ni2MoVNb steel,which is a novel transmission gear material for high power density gearboxes.The effect of shot peening and surface ultrasonic rolling process parameters on the microhardness,surface morphology and roughness are studied,and the surface strengthening process parameters are optimized.Moreover,a novel surface treatment method of combining shot peening and ultrasonic surface rolling is proposed,the wear principles and the strengthening mechanism of contact fatigue after different surface treated methods are revealed.The main contents are listed as follows:Aiming at the problem of gear failure of high power density gearbox,the main failure forms of gearbox gears,the components and related mechanical properties of gear steels currently used at home and abroad are described,and the main surface strengthening technologies applied on the gear surfaces are elaborated.The objective and main research contents of this work are further discussed.The effects of different parameters of shot peening and surface ultrasonic rolling on the microstructure,microhardness,surface morphology and roughness of 17Cr2Ni2MoVNb steel are studied by experiments.The surface treatment method of combining shot peening and ultrasonic surface rolling is proposed,and the influence on microstructure,microhardness,surface morphology and roughness also evaluated.Moreover,the internal strengthening mechanism of the samples after different surface strengthening treatments are clarified.After the combined surface treated,the samples not only have higher microhardness and residual compressive stress,but also have good surface quality.At the same time,they have the advantages of shot peening and surface ultrasonic rolling,and makes up for the shortcomings of the two strengthening methods.The optimized composite strengthening samples can have finer grain size,higher microhardness and better surface quality.Based on the theoretical analysis of surface shot peening and ultrasonic rolling contact theory,the Johnson-Cook constitutive equation is used to construct a numerical simulation model of surface shot peening,ultrasonic rolling and their composite strengthening.Analyze the law of material deformation in the contact area during the strengthening process through the contact theory model,determine the main parameters affecting the deformation of surface shot peening and ultrasonic rolling,and provide theoretical basis for the numerical simulation of surface shot peening and ultrasonic rolling.The numerical simulation model is used to study the influence of different strengthening parameters on impact force,deformation and residual stress.The residual stress test values and simulation values at different positions of surface and subsurface are compared and analyzed.It is verified that the models of the multi-shot peening,surface ultrasonic rolling and their combined model have high simulation accuracy for residual stress prediction.And obtain the influence law of different strengthening parameters on residual stress,which lays a theoretical foundation for strengthening mechanism analysis.The effect of different surface strengthening treatments on the friction and wear properties of 17Cr2Ni2MoVNb steel are studied.The wear morphology and wear mechanism after different surface strengthening treatments are clarified,the strengthening mechanism of different surface treatment methods under friction and wear environment are revealed.The influence of different surface treatments on contact fatigue properties of 17Cr2Ni2MoVNb steel are studied.The contact fatigue life of the samples after different surface treatments are analyzed by using Weibull distribution.The failure mechanisms of contact fatigue are determined by combining the damage morphology of the samples,and the strengthening mechanisms of different surface strengthening methods under the contact fatigue environment are revealed.