In this work, the passivation and localized corrosion of selective laser melted (SLM) stainless steel 316 L when exposed to high pressures of CO₂ with the presence of H₂S and Cl⁻ at 25 °C and 125 °C were studied. Depletion of Cr/Mo was observed at the cell interiors and melt-pool boundaries (MPBs) compared to the cell boundaries. Volta potential differences obtained from scanning Kelvin probe force microscopy (SKPFM) showed that the MPBs were 8–20 mV lower than the matrix, while the cell interiors were 20–50 mV lower than the cell boundaries. Electrochemical impedance spectroscopy (EIS) and Mott–Schottky tests indicated a more defective passive film at 125 °C, and X-ray photoelectron spectroscopy (XPS) confirmed the formation of a less protective film with an increased S/O ratio at 125 °C than 25 °C. Initiation of localized corrosion was observed at the MPBs and pits formed after a week of immersion were wider by an order of magnitude at 125 °C than 25 °C, with evidence of cell-interior dissolution. While passivity was observed even at elevated temperatures, local chemical heterogeneities compromised the stability of the film and contributed to localized corrosion in SLM SS316L.

The effect of temperature on the localized corrosion resistance and passive film characteristics of laser powder-bed fusion (LPBF) 316L (UNS S31603) was studied in a buffered 3.5 wt% NaCl solution at 25, 50, and 75 °C. DC techniques such as cyclic potentiodynamic polarization showed lower passive current densities, high breakdown potentials, and a higher resistance to initial breakdown compared with wrought 316L samples at all temperatures. However, LPBF 316L was more susceptible to metastable pitting at potentials before film breakdown and higher damage accumulation post film breakdown. AC techniques, such as Mott–Schottky analysis and electrochemical impedance spectroscopy, showed that the formed passive film was more robust on the LPBF 316L samples at all temperatures, accounting for the higher initial resistance to pitting. However, with increasing temperatures, the film formed had an increasing concentration of defect density. Passive compositions at the various test temperatures studied using X-ray photoelectron spectroscopy (XPS) showed that the LPBF samples showed higher amounts of Cr and Fe oxides and hydroxides compared with the wrought samples, which made the passive films on the LPBF samples more compact and protective. Investigation of the pits formed on the LPBF showed the preferential regions of attack were the melt-pool boundaries and cell interiors due to their being depleted of Cr and Mo when compared with the boundaries and matrix.

Steel rebars are widely applied in reinforced concrete structures due to their contribution to significant improvements in mechanical properties. However, exposure to corrosive environments, such as solution-containing chloride, may induce an accelerated corrosion and jeopardize the sustainability and durability of reinforced concrete. The current work evaluated the chloride thresholds (in both wt% and [Cl−]/[OH−]) of steel rebar with different chromium contents (0 wt%, 4 wt%, and 23 wt%) in synthetic concrete pore solution based on AC and DC electrochemical measurements, and chemical and structural characterizations. The study found that the chloride threshold (CT) values varied slightly based on the different measurement methods and the values were compared with values obtained from the literature. The values are 0.01 wt% to 0.1 wt% (3.76), 0.1 wt% to 1 wt% (>23.8), and 2.9 wt% to 3.5 wt% (>23.8) for 615, 4% Cr, and SS23, respectively, where the values in parentheses are [Cl−]/[OH−]. Therefore, it is demonstrated that multiple measurements are necessary to determine a reliable CT value. Corrosion mechanisms giving rise to CT are included to illustrate the processes involved in establishing CT.