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 natu ral seawater, the probability of the occurrence of the crevice corrosi on was not dependent upon the nitrogen content, while the penetration depth was decreased with increased nitrogen content. The electrochemic al measurements were carried out to clarify the effect of nitrogen on each stage: initiation, propagation and repassivation. The acidificati on of anolyte and the active dissolution were suppressed by the additi on of nitrogen. Also, the transient current for passivation after poli shing revealed that the nitrogen kinetically accelerated the passivati on in acidic chloride environments. On the other hand, the nitrogen wa s found to have no effect on the depassivation pH (pH(D)) and the repa ssivation potential (E(R)). The concentration of ammonium ion in the a nolyte was increased with increasing nitrogen content. The beneficial effect of nitrogen was considered to be in prolonging the incubation p eriod and decreasing the penetration rate by the formation of ammonium ion from the alloyed nitrogen.