INFLUENCE OF NITROGEN ON THE PASSIVITY OF 18-8 (0. 24% N) STAINLESS STEELS.

Increasing the N content of a commercial grade 18-8 Stainless steel from 0. 04% to 0. 24% N was found to raise the breakdown potential from 200 mV to 304 mV in deaerated 0. 1M HCl (pH 1. 2). In deaerated 0. 5M H//2SO//4 plus 0. 5M NaCl (pH 0. 4) the 0. 04% N alloy pitted at 448 mV. The 0. 24% N alloy exhibited breakdown at 448 mV, a pitting inhibition potential at 540 mV, and a final pitting potential at 640 mV. Variable angle XPS studies of the passive film formed on the 0. 24% N alloy at 0 mV after 10 seconds and 1 hour provided evidence of the role of N and SO//4** equals in the initial stages of repassivation. The N was found to exist in three forms, namely CrN (397. 1 eV) at the metal-film interface, a complex of NH//3 or NO (399. 6 eV) distributed throughout the passive film, and an ammonium salt (401. 5 eV) observed at the passive film-solution interface.