Effect of “475 °C embrittlement” on duplex stainless steels localized corrosion resistance

The influence of the 475 °C ageing treatment on the localized corrosion resistance of austenitic-ferritic (duplex) stainless steels has been investigated by means of double loop electrochemical potentiodynamic reactivation (DL-EPR) and potentiostatic tests. The effect of different ferrite/austenite (α/γ) volume fractions has been also considered. For this purpose, two different 22 Cr 5 Ni duplex stainless steels, with different α/γ ratios (respectively equal to 1 and 1.5) have been investigated. The ageing treatment at 475 °C was conducted up to 1000 h. The resulting microstructural modifications were analyzed with transmission electron microscopy observation. The microstructure resulting from solid state transformations, like spinodal decomposition and G-phase precipitation, were characterized and the relevant mechanisms identified. An evident influence of the ferrite and austenite volume fraction on the G-phase formation and spinodal decomposition kinetics were found. The effects on the localized and selective corrosion attack susceptibility were also investigated.