Tailoring the microstructural and mechanical properties of 316L stainless steel manufactured by laser powder bed fusion

Abstract

The grains, cellular structures, dislocation densities, and oxides in L-PBF 316LSS were systematically characterized. The microstructure evolution and mechanical properties were closely associated with the scanning speed. The sizes of grains and oxides in L-PBF 316LSS significantly decreased with increasing scanning speed, while the dislocation density remained relatively stable for speeds from 500 to 900 mm s−1 and significantly increased when the scanning speed exceeded 900 mm s−1. The tensile samples exhibited obvious anisotropic mechanical properties, and the TD samples showed higher strength, attributed to the strong <110> crystallographic orientation, while <111>-oriented grains facilitated activation and generation of deformation twins. Importantly, the cellular substructures were traversed by deformation twins, leading to their subdivision and dissociation. The discontinuous dislocation tangles interacted with deformation twins and provided a continuous and stable work hardening capability, resulting in superior ductility of BD samples. Reasonable agreement between the yield strength experimental results and theoretical calculations was achieved, suggesting that the superior strength and ductility for L-PBF 316LSS can be attributed to the grain boundary strengthening, oxide dispersion strengthening, dislocation strengthening and work hardening behavior. Collectively, this study revealed the strengthening mechanism of L-PBF 316 L stainless steel, which can provide theoretical guidance in the development of new alloy materials.