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

摘要

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