A STATISTICAL STUDY OF THE ROLE OF MOLYBDENUM IN THE PITTING RESISTANCE OF STAINLESS-STEELS

The local breakdown of passive films grown on stainless steels in the presence of chloride ions generally leads to pitting. To study this ph enomenon, the pitting potential of several stainless steels in neutral chloride media has been determined, by a statistical technique. This parameter is obtained when the statistical pit generation rate corresp onds to a preset critical value. Two cases were considered: (a) stainl ess steels without alloyed Mo (AISI 430 or 304) in NaCl or NaCl + Na2M oO4, aerated or de-aerated, solutions, and (b) Mo alloyed stainless st eels (AISI 434 or 316) in NaCl aerated or de-aerated solutions. The ex perimental results are compared, and discussed in terms of the influen ce of alloyed or dissolved molybdenum. It appears that the role of thi s element is different in each case, and also that dissolved oxygen in the solution plays a significant role in the improvement of the passi vity due to molybdate ions action.