Microstructure and mechanical properties of laser shock peened 38CrSi steel

Laser shock peening (LSP) induces severe plastic deformation and high compressive residual stress in the metal surface, which can effectively enhance mechanical properties. In this work, the effects of LSP on the microstructure, microhardness, residual stress, tensile and fatigue properties of 38CrSi steel were investigated. After LSP, high-density dislocations such as dislocation walls, dislocation cells, and deformed cementite lamellae structures were observed in the surface layer. The dislocation density was roughly calculated by TEM images. Surface microhardness strengthened by dislocations increased by 24%. The maximum value of compressive residual stress reached 404 MPa. The depth of residual stress affected layer was 750 mu m. The peening area had a great influence on the fatigue property. Compared with the base metal (BM), the fatigue life of specimens peened on Area I was improved by 76%, while the fatigue life of specimens peened on Area II was improved by 125%. Finite element analysis revealed that the compressive residual stress induced by LSP in the whole edge of specimen peened on Area II was the main factor for further improving fatigue property. The relationship between compressive residual stress field and crack path was investigated to clarify the strengthening mechanism in different peening areas.