An Investigation on Fatigue Strengthening Mechanism of 316L Stainless Steel Welded Joint by Surface Mechanical Rolling Treatment

ABSTRACT Surface mechanical rolling treatment (SMRT) effectively enhances the fatigue strength and fatigue ductility of 316L stainless steel, demonstrating great potential for application in welded structures. In this work, static tensile experiments and fully reversed strain‐controlled fatigue experiments were performed on both as‐welded and SMRT‐processed 316L specimens. Results show that both fatigue strength and fatigue ductility increased after SMRT processing. The average surface grain size was refined to ~1.62 μm (vs. 22 μm in base metal and 102 μm in weld zone core regions), while ultimate tensile strength increased by 13.8% (from 632 to 719 MPa). The fatigue strength of SMRT‐processed specimens increased by approximately 26% (from 270 to 340 MPa) at 10 6 cycles compared to as‐welded specimens. A significant fatigue life enhancement of 640% was observed at 0.20% strain amplitude. Following SMRT processing, crack initiation occurred in the weld zone (WZ), transitioning from surface to subsurface locations at strain amplitudes below 0.6%. In contrast, crack initiation occurred at surface locations in the base metal (BM) of as‐welded specimens. Gradient nanostructures, compressive residual stresses, and martensitic phase transformation induced by SMRT collectively contribute to the enhanced fatigue strength and ductility of the 316L welded joint.