Laser powder bed fusion (L-PBF) is an advanced additive manufacturing technique for producing stainless steel components having intricate geometries. Understanding the oxidation and electrochemical behaviour of L-PBF stainless steels is essential for their potential application in high temperature aqueous environments. This study investigates the influence of stress relieving (SR), solution annealing (SA), and hot isostatic pressing (HIP) on the corrosion behaviour of L-PBF 316L in an oxygenated simulated pressurized water reactor (PWR) environment. In situ electrochemical impedance spectroscopy (EIS) was combined with ex situ Raman spectroscopy, X-ray photoelectron spectroscopy, and analytical electron microscopy to characterize the electrochemical response and oxide films. Results indicate that post-heat treatment substantially modifies the L-PBF-derived microstructure, including grain-boundary character, cellular dislocation structure, and precipitate morphology, thereby influencing local oxidation pathways and oxide-film characteristics. Cross-sectional observations revealed differences in oxide morphology and thickness among the heat-treatment conditions, whereas the overall electrochemical response remained relatively similar. Mixed-Conduction Model analysis further showed that the differences in the electrochemically detectable transport and interfacial reaction parameters were relatively modest. Under the highly oxidizing test condition, chromium depletion from the inner oxide was promoted, consistent with preferential chromium dissolution and/or redistribution and the development of a Cr depleted Ni-Fe rich spinel oxide. Although heat treatment modifies local oxidation behaviour and oxide-film characteristics, these effects do not translate into proportionally large changes in the integrated electrochemical response. The findings provide mechanistic insight into the relationship between heat-treatment-induced microstructural evolution and oxide development of L-PBF 316L under the investigated highly oxygenated high temperature aqueous conditions.
