THE INFLUENCE OF NITROGEN AND MOLYBDENUM ON PASSIVE FILMS FORMED ON THE AUSTENOFERRITIC STAINLESS-STEEL-2205 STUDIED BY AES AND XPS

Passivation of the austeno-ferritic (duplex) stainless steel 2205, and the corresponding austenitic and ferritic single phase alloys, has be en studied with Auger electron spectroscopy (AES) and X-ray photoelect ron spectroscopy (XPS) with a focus on the lateral and depth distribut ions of nitrogen and molybdenum in and near the passive layer. The res ults can be explained by the bipolar model of the passive film; the fi lm is stabilised by the interaction of molybdates and ammonium ions on the surface. The synergism between nitrogen and molybdenum is of part icular importance for duplex stainless steels, since they owe part of their corrosion resistance to interaction between the nitrogen-rich au stenite and the molybdenum-rich ferrite.