Effect of alloying nitrogen on crevice corrosion of austenitic stainless steels

The effect of alloying nitrogen was investigated on crevice corrosion of the 10%Mn-25%Ni-25%Cr-(0 similar to 0.36)%N austenitic steels. From the immersion test results for the multiple crevice specimens in natural seawater, the probability of the occurrence of the crevice corrosion was not dependent upon the nitrogen content, while the penetration depth was decreased with increased nitrogen content. The electrochemical measurements were carried out to clarify the effect of nitrogen on each stage: initiation, propagation and repassivation. The acidification of anolyte and the active dissolution were suppressed by the addition of nitrogen. Also, the transient current for passivation after polishing revealed that the nitrogen kinetically accelerated the passivation in acidic chloride environments. On the other hand, the nitrogen was found to have no effect on the depassivation pH (pH(D)) and the repassivation potential (E(R)). The concentration of ammonium ion in the anolyte was increased with increasing nitrogen content. The beneficial effect of nitrogen was considered to be in prolonging the incubation period and decreasing the penetration rate by the formation of ammonium ion from the alloyed nitrogen.