Mechanisms of synergistically enhanced strength and plasticity in 316L stainless steel fabricated by laser powder bed fusion via cold rolling and annealing treatments

The effect of the cross-scale interfaces on the strengthening mechanism of laser powder bed fusion processed (L-PBFed) 316L stainless steel was investigated by nanoindentation, rolling-annealed and tensile test. The cellular sub-grain with high density dislocations and element segregation supressed dislocation nucleation and move, acting as grain boundary during deformation. The cellular sub-grain showed high stability despite of rolling and annealed. Rolling-annealing induced a bimodal grain size distribution in additively manufactured stainless steel. This strategy retained the grain boundary strengthening effect from cellular boundaries while introducing high-density dislocations to elevate yield strength. Concurrently, localized recrystallized grains modulated strain distribution, enabling more uniform deformation and promoting widespread deformation twin formation, thereby enhancing plasticity. These findings demonstrate that optimizing grain size while preserving cellular structure strengthening offers a viable pathway to improve the comprehensive mechanical properties of materials.