THE ROLE OF NITROGEN IN THE PASSIVITY OF AUSTENITIC STAINLESS-STEELS

Three austenitic stainless steels (a Fe-17Cr-13Ni-0.15N alloy, an ultr a pure Fe-18Cr-10Ni alloy and a type 304 stainless steel) were used in this study in order to investigate the effect of nitrogen on the elec trochemical behaviour and on the nature of the passive film formed on the steels in acidic solution (0.5 M H2SO4). The presence of nitrogen in the alloy does not apparently have a significant influence on the r esponse of the material to anodic polarization in the acid electrolyte . Surface analysis of the alloys by XPS after passivation shows that n itrogen is enriched at the surface by anodic segregation during dissol ution and passivation of the nitrogen-bearing alloys. After passivatio n of the alloys three chemical states of nitrogen are detected in the N 1s spectrum. The peak at low binding energy (397.7 +/- 0.1 eV) corre sponds to nitrogen bonded essentially to chromium under the form of a nitride which is incorporated in the passive film. The N 1s peaks obse rved at higher binding energies (400.2 +/- 0.1 and 402 +/- 0.1 eV) cor respond to nitrogen species located on the surface of the passivated a lloys, which are produced by reaction of the alloy surface with the so lution.