The Effect Of The Carburized Shot-peening Process On The Metamorphic Layer Generation And The Bending Fatigue Life Of Carburized Gear

As a key component of mechanical transmission equipment,gear is worked in the harsh alternating load environment,to which fatigue is the main failure mode.Shot peening is the main mean to improve the fatigue life,because the residual compressive stress and surface grain refinement can be introduced in the gear surface,forming a metamorphic layer which effectively inhibit the initiation and expansion of the crack.In this thesis,the relationship in shot peening parameters,metamorphic layer and fatigue life is studied based on extensive research about improving the fatigue life of materials.18CrNiMo7-6 gears were shot peened to characterize the changes of the parameters to study the effect on the formation of the metamorphic layer using different shot peening processes,and to find the relationship between the metamorphic layer and the bending fatigue life of the gears.The research content includes the following aspects:(1)In view of the complex random characteristics of the surface after shot peening,the multi-scale analysis of surface morphology is carried out.The optimal evaluation scale of surface morphology is given for different shot peening parameters(shot peening strength,shot peening diameter,shot peening coverage),which greatly facilitates the correlation analysis between process parameters and morphology.(2)The metamorphic layers are characterized by surface morphology,residual stress(depth distribution),microhardness(depth distribution)and microstructure.Through their characterization and analysis,the qualitative relationships in shot peening process,fatigue life and metamorphic layer are established.The results show that increasing the shot peening strength,the residual stress and surface hardness of the surface layer are increased,and the surface martensite structure is made more compact.Hence,the gear bending fatigue life is improved.By changing the shot diameter,the surface morphology and surface residual stress are effectively optimized,thus affect the fatigue life.Increasing the shot peening coverage can effectively improve the maximum residual compressive stress depth and surface morphology.(3)Through studing the effect on the formation of the metamorphic layer and bending fatigue life by changing shot peening process parameters,the optimal analysis of the shot peening process is carried out.The subject has certain guiding significance for the optimization of shot peening process.