Effects of Mn on the localized corrosion, repassivation kinetics, and stress corrosion cracking ͑SCC͒ of high Mn-N stainless steels ͑SSs͒ were examined in chloride solutions and compared with those of type 304 SS. The resistance to pitting corrosion of high Mn-N SSs decreased with an increase in Mn content at the expense of Ni. Repassivation kinetics of the high Mn-N SSs was analyzed by the relationship between the current density i͑t͒ and the charge density q͑t͒ that has flown from the scratch; passive film initially nucleated according to the place exchange model and then grew according to the high-field ion conduction model in which log i͑t͒ vs 1/q͑t͒ has a linear relationship with a slope ͑cBV͒. The repassivation rate of the alloys, analyzed by the ͑cBV͒ value, was decreased with an increase in the Mn content. The resistance to SCC of the alloys measured in 25% MgCl 2 was in good agreement with that predicted, based on their repassivation rate. The deleterious effects of Mn on the localized and stress corrosion of the alloys appear to be associated with an increase in number and size of nonmetallic inclusions such as ͑Mn, Cr͒ oxides with Mn content.

Effects of the alloying elements, Sn and Sb, on the corrosion resistance of modified AH 32 steel for the cargo oil tanks (COT) were examined using an electrochemical test and weight loss measurement. All experiments were carried out in acidic chloride solution (0.14 M HCl and 10 wt% NaCl, pH 0.85) at 30°C, simulating the inner bottom plate of COT. It was clearly found that the small amount addition of Sn and Sb improved the corrosion resistance of modified AH 32 steel, which is confirmed by the higher polarization resistance of AH 32 steel modified with Sn and Sb addition compared with that of the base steel. X-ray photoelectron spectroscopy analysis of the corroded surface after immersion of 72 h presented that the AH 32 steel modified with Sn and Sb addition created the protective corrosion products including SnO2 and Sb2O5. These oxides act as high corrosion inhibitor to anodic corrosion reaction, and hence leading to the improvement in the corrosion resistance of the modified AH 32 steels.