Aspects of the anodic behaviour of duplex stainless steels aged for long periods at low temperatures

Duplex stainless steel samples were aged at low temperatures (300 and 400 °C) for 1000 and 2000 h. Their anodic behaviour was studied in a 0.1 N concentration of sulphuric acid, which revealed that the polarisation curves were dependent on the aging temperature and time. Complex anodic current peaks occurred at low and high potentials due to the dual austenite and ferrite microstructure. The aging treatment promoted silicon enrichment of the passivated film, probably over the austenite phase, as indicated by X-ray photoelectron spectroscopy measurements. G phase precipitation and spinodal decomposition was identified by transmission electron microscopy.