MECHANISM OF PASSIVATION IN STAINLESS STEELS CONTAINING HIGH CONCENTRATIONS OF NITROGEN.

An austenitic stainless steel containing 6% Mo and 0. 45% N has been studied in the solution annealed condition using electrochemical and surface analytical techniques. After passivation there is an enrichment of nitrogen at the metal-passive film interface. The N(ls) binding energy at this interface is typical of interstitial, atomic nitrogen. Nitrogen is nearly perfectly retained during passive dissolution in 0. 5 M H//2SO//4 or in 0. 5 M HCl plus 2 M NaCl. In chloride solutions, enrichment of both molybdenum and nitrogen is believed to occur at breakdown sites where a more aggressive environment develops. This process is simulated using a 4 M HCl solution.