Build direction–mediated microstructural regulation of passive film stability in selective laser melted 316L stainless steel

This study systematically investigates the influence of build directions (BDs) (0°, 45°, 90°) on the passive film stability of selective laser melted (SLM) 316L stainless steel in a simulated marine environment (3.5 wt.% NaCl solution). Through a combination of microstructural characterization, residual stress measurement, and electrochemical testing, the intrinsic mechanisms by which BD governs corrosion resistance via the modulation of grain orientation, texture, residual stress and dislocation density were elucidated. The results indicate that the 0° BD specimen, characterized by a high fraction of <111>-oriented grains, moderate grain size, the highest proportion of low-angle grain boundaries, and the highest geometrically necessary dislocation density, formed the most compact and stable passive film. In contrast, the 45° built specimen exhibited the poorest corrosion resistance due to coarse grains and unfavorable texture, while the 90° BD specimen showed intermediate performance. Analysis of passive film kinetics and pitting morphology further corroborated this performance hierarchy. This work provides critical insights for tailoring the microstructure through SLM processing to enhance the service reliability of additively manufactured stainless steel components in aggressive environments.