Effect of the initial microstructure on the residual stress in the 20Cr₂Ni₄ gear steel subjected to laser shock peening and shot peening

ObjectiveThe influence of the initial surface topography on the residual compressive stress distribution along the depth direction of targets under laser shock peening (LSP) and shot peening (SP) processes was investigated.MethodsA finite element model for the composite strengthening of 20Cr₂Ni₄ gear steel was established using the finite element software. Simulation analyses were conducted on the surface of this model for laser shock peening, shot peening, and composite strengthening respectively under different initial topographical conditions.ResultsThe results indicate that, with the increase of initial surface roughness, the peak residual compressive stress and stress layer depth along the depth direction of the target decrease under SP. In contrast, no significant variation in the stress layer depth under LSP is found. Under combined the strengthening, the residual compressive stress distribution shows distinctive segmented combination characteristics along the depth direction. Notably, the depth of the compressive stress layer is reached to three times that of SP, and the peak residual compressive stress is doubled compared to LSP. Compared to LSP alone, the internal stress layer depth is decreased from 0.42 mm to 0.36 mm (a 14.3% reduction) after the combined strengthening. Additionally, higher peak residual compressive stress is achieved and the adverse effects of initial surface roughness on stress distribution are mitigated by the combined strengthening.