Corrosion of additively manufactured stainless steel 304L in relation to grain texture and process-induced defects: A localized analysis

Abstract

This study investigates the relationship between microstructure and corrosion resistance of stainless steel 304L (SS304L) fabricated using the laser powder bed fusion (L-PBF) additive manufacturing (AM) method. The properties of the AM material are characterized through Electron Backscatter Diffraction (EBSD) and Scanning Electrochemical Microscopy (SECM) for microstructural analysis, along with cyclic polarization (CP) and electrochemical impedance spectroscopy (EIS) for assessing corrosion behavior. Results for the AM material are compared with its wrought counterpart. The findings reveal significant effects of grain attributes on corrosion properties. The finest-grained wrought material exhibits superior corrosion resistance, while the AM specimen shows minor variations. The top plane, oriented perpendicular to the build direction, of the AM specimen demonstrates unique characteristics due to its finer grain size. Grain size heterogeneities, particularly in this plane, lead to increased pitting initiation and the formation of smaller pits. Conversely, larger grains with greater surface area promote pit formation within the grains. This work further contributes to the study of localized characterization of pitting by using SECM to measure spatial and temporal currents near process-induced defects. SECM results demonstrate higher tip currents within these defects compared to surrounding surface, indicating that initial corrosion preferentially occurs within these defects. However, as exposure time increases, defect activity evolves, leading to an increased surface activity in their vicinity.