Gradient microstructure evolution of high-strength alloy steel induced by shot peening

Shot peening can enhance the fatigue performance of materials, which is closely related to its improvement of material microstructure. However, research on the evolution of microstructures and mechanical properties during the shot peening process remains insufficient, hindering the understanding of strengthening mechanisms and process optimization, particularly for high-strength 9310 alloy. To address this, this study proposes an advanced numerical simulation method to characterize the influence of high-speed particle impacts on the microstructure and mechanical properties of 9310 high-strength alloy. The proposed model was validated through electron backscatter diffraction (EBSD) and X-ray diffraction experiments, demonstrating excellent agreement between simulations and experimental results. The results demonstrate significant microstructural refinement, with surface cell size decreasing from 8.5 μm to 2 μm post-shot peening. Increasing shot diameter from 0.3 mm to 0.9 mm reduces surface residual stress from −1000.30 MPa to −754.36 MPa while expanding the modified layer from 100 μm to 300 μm. Elevated shot velocity (45–105 m/s) enhances plastic deformation, reducing cell size from 1.31 μm to 0.98 μm and increasing dislocation density from 2.21 × 10⁹ mm⁻² to 2.81 × 10⁹ mm⁻², albeit with reduced surface compressive stress. This refined microstructure, formed under high-speed particle impacts, significantly improves mechanical properties (e.g., yield stress), surpassing results obtained from previous Hopkinson bar tests. Additionally, the magnitude of microstructural changes increases nearly proportionally with coverage up to 200 %. These findings provide deeper insights into the mechanisms of shot peening strengthening and contribute to the advancement of shot peening processes.