THE INFLUENCE OF NITROGEN ON THE PASSIVATION OF STAINLESS-STEELS

Two austenitic stainless steels, Fe-20Cr-20Ni-6Moo-0.011N and Fe-20Cr- 20Ni-6Mo-0.2N were polarized in 0.1 M HCl + 0.4 M NaCl at 22 and 65 de grees C. Fitting is initiated on both steels. The high N-containing st eel is repassivated while the pits are growing on the low N-containing steel at 65 degrees C. The composition and the thickness of the passi ve films (determined by ESCA) formed during polarization to the potent ials -75, +500 and +800 mV (SCE) are independent of the N content of t he steels. Nitrogen segregates anodically to the metal-oxide interface during passivation. A model for a synergistic effect between Mo and N is suggested. Copyright (C) 1996 Elsevier Science Ltd.