Synergistic effect of Ni and N on improvement of pitting corrosion resistance of high nitrogen stainless steels

The pitting corrosion resistance of Fe18Cr10Mn(0.33-0.69) N, Fe18Cr10Mn1Ni(0.33-0.84) N, and Fe18Cr10Mn0.35N(0-3) Ni alloys were investigated. The pitting potential increased as the N content increased in both Fe18Cr10Mn(0.33-0.69) N and Fe18Cr10Mn1Ni(0.33-0.84) N alloys. The rise in the pitting potential was more pronounced in Fe18Cr10Mn1Ni(0.33-0.84) N alloys than in Fe18Cr10Mn(0.33-0.69) N alloys. However, it was found that Ni alone had no effect on the pitting corrosion resistance of Fe18Cr10Mn0.35N based alloys. Thus, it was concluded that the alloyed N worked synergistically with Ni to promote the pitting corrosion resistance in Fe18Cr10Mn based alloys. Analyses of passive films of Fe18Cr10Mn(0.33-0.69) N and Fe18Cr10Mn1Ni(0.33-0.84) N alloys revealed that N was incorporated into the passive film, with N enriched at the film/metal interface. However, the alloyed N increased the Cr cation fraction in passive films of Fe18Cr10Mn1Ni(0.33-0.84) N alloys, whereas N decreased in that of Fe18Cr10 Mn(0.33-0.69) N alloys. This difference was considered as the reason for the synergistic effect between N and Ni in Fe18Cr10Mn based alloys.