The rapid melting and solidification cycles in Laser Powder Bed Fusion (LPBF) 316L stainless steel create microstructural defects and residual stresses that modify corrosion behavior. One way of countering these defects is through post-processing heat treatments. While current literature discusses how heat treatments dissolve defects, their influence on the surface film characteristics of corroded SS316L needs further understanding. The research question for this Research in Progress is: How do microstructural defects influence the formation and stability of passive films in heat treated LPBF SS316L? Four parameter sets (C1–C4) were printed using laser power and scan speed combinations selected from literature process maps. C1 (50 W, 500 mm/s) was tuned to promote large lack-of-fusion (LOF) pores, C2 (50 W, 1000 mm/s) produced keyhole-type porosity, while C3 (150 W, 500 mm/s) and C4 (150 W, 100 mm/s) produced dense, well-fused tracks with minimal porosity. As built potentiodynamic polarization tests in 3.5 wt.% NaCl show a link between defect regime and corrosion response. Overlaid curves indicate that C1 experiences the earliest passive-film breakdown and highest pitting susceptibility due to LOF regions acting as preferential sites for localized attack. C2 exhibits intermediate behavior with pits initiating near keyhole pores, while the high-density builds (C3 and C4) maintain extended passive regions, higher breakdown potentials, and reduced pit density, confirming that higher volumetric energy input and sound fusion improve passive film stability. The next stage of this project applies controlled post-build heat treatments to a subset of C1–C4 samples, including a subcritical stress-relief anneal (~800 °C) aimed at reducing residual stresses and partially homogenizing Mo/Cr segregation while preserving some cellular structure. A higher-temperature solution treatment (~1050-1100 °C, water-quenched) will also be used to homogenize the microstructure and eliminate segregation without causing sensitization or sigma phase. The time frame for the heat treatment steps will also be investigated as part of the study. Repeated electrochemical testing (potentiodynamic scans and electrochemical impedance spectroscopy), combined with surface-film and defect characterization, will compare as-built and heat-treated states in terms of corrosion potential, passive current density, passivation behaviour, and the role of LOF and keyhole defects after heat treatment. The anticipated outcome is a process-structure-corrosion map that links LPBF parameters (C1–C4) with heat-treatment schedules to identify conditions that minimize defect driven attack while maintaining or enhancing passive-film performance for additively manufactured SS316L in chloride environments.
