Improving mechanical properties of additively manufactured H13 steel through residual stress modulation by laser shock peening

The high tensile residual stresses in the laser powder bed fusion (LPBF) manufactured H13 steel lead to severe cracks and low mechanical properties. To solve this problem, the laser shock peening (LSP) was applied to H13 steel manufactured by LPBF to eliminate tensile residual stress and improve mechanical property. The evolution mechanism of defects and residual stress during LPBF-LSP process were accounted for using the finite element method. The numerical results indicate that the compressive residual stress induced by LSP shock was beneficial for pores and cracks closure. A single shock cannot completely eliminated the tensile residual stress generated in LPBF process, and the mechanism of tensile residual stresses elimination by shock wave and rarefaction wave was proposed. The LSP process parameters of LPBF manufactured h13 steel were optimized by single point impact tests, and the effects of residual stress induced by LSP on defect, microstructure, and nano-hardness were experimentally studied. The experimental result shows that the defect closure zone depth increases with the number of laser impacts. The nano-hardness near the surface was increased by 31% than the LPBF sample after double LSP treatment. The strengthening mechanism of LSP-H13 was clarified as dislocation strengthening. This work verifies the feasibility of tensile residual stress elimination and mechanical properties improvement of the LPBF manufactured H13 steel by LSP treatment.