Characterization of Passive Films Formed on Manganese Nickel-Free Stainless Steel Exposed to Simulated Concrete Pore Environment

摘要

Manganese is a key component in low-cost SS formulations when nickel is replaced by Mn. Passive layers grown on Cr18Mn12 free-nickel SS samples immersed in saturated Ca(OH)_2 and Portland cement extract, were studied. The corrosion behavior of the grown passive films was monitored at open circuit potential. In the presence of chloride ions the passivation process is perturbed and competes with the dissolution one. The surface becomes irregular, rough and Mn was found enriched in areas of non metallic inclusions in the passive layer, while the Fe/Mn and Fe/Cr ratios tend to decrease. The formed film is N-richer at the metal-oxide interface, as a consequence of its anodic segregation during dissolution-passivation process. Surface protuberances in the morphology of the SS could be explained in terms of unattacked oxide inclusions that still remain in the formed passive film or due to manganese insoluble compounds, which aid the corrosion resistance of the studied steel.