Surface hardening analysis in shot peening of AISI 9310 gear steel driven by grain and dislocation coupling effects

The complexity of the microstructure evolution, the difficulty of characterization of the microstructure and the uncertainty of the relationship between multiple process parameters and micro-hardness bring great challenges to the modeling and analysis of the surface hardening of shot peening. To overcome these bottlenecks, a hardening model driven by grain and dislocation is established and verified by experiments. The results of electron back scatter diffraction(EBSD) analysis after shot peening highlight the complex evolution behavior of grain and dislocation during shot peening, which is significantly dependent on microplastic deformation. On this basis, based on the dislocation density constitutive model and the Abaqus subroutine VUMATt, a theoretical model of AISI 9310 shot peening surface hardening was established considering the factors of microplastic deformation, grain and dislocation. The simulation results of the model agree well with the experimental results, and the average error is less than 10 %. The results show that the increase of coverage has a great influence on the micro-hardness of depth less than 50 μm. When the coverage exceeds 200 %, the increase of residual stress decreases significantly. The research results not only deepen the understanding of the microstructure evolution and hardening mechanism of high strength gear steel, but also provide theoretical guidance for optimizing the microstructure of high strength gear steel to obtain high wear resistant surface.