Effect of nitrogen on crevice corrosion and repassivation behavior of austenitic stainless steel

Austenitic stainless steels were produced based on a Fe-23mass%Cr-4mass%Ni alloy with varying nitrogen (0.7–1mass%) and molybdenum contents (0–1mass%), through electro-slag remelting (ESR) under high nitrogen gas pressure. The effects of nitrogen on crevice corrosion behavior in an acidic chloride solution were investigated, and the passive film of the crevice corrosion area after corrosion tests was analyzed using X-ray photoelectron spectroscopy (XPS). At the same time, the effects of nitrogen on the passivation behaviors after scratching were also investigated. During crevice corrosion at a noble potential of 0.7V (SCE), the nitrogen in solid solution in the steel dissolves into the solution as NO3 , and its concentration increases with the nitrogen content in the steel. It was also established that the number of corrosion spots, the corrosion loss, and the maximum depth of corrosion all decrease with the increase in the nitrogen content present in the steel and the applied potential. Such results can be attributed to the presence of NO3 dissolved into the aqueous solution. On the other hand, results from scratch tests show that the increase in the amount of added nitrogen decreases the peak value of passivation current as well as the amount of electricity during repassivation, suggesting that nitrogen stimulates the passivation process and suppresses the occurrence of crevice corrosion. XPS analysis shows the presence of nitrogen as nitrides and NH3 in the surface layer of crevice corrosion and the internal layer of passivation films. [doi:10.2320/matertrans.MRA2007273]