Abstract
Electrochemical potentiokinetic reactivation (EPR) tests were carried out for the Fe-28Cr-5Ni ferritic stainless steel aged at 450°C for up to 5000h. The unaged steel showed a reactivation peak and this is attributed to the Cr-depleted zone in the vicinity of carbides. The ageing at 450°C promotes the diffusion of Cr into the Cr-depleted zone and the Cr-depletion recovers. However the ageing produces new reactivation peaks and severe pitting attacks in the grains were observed for the steel aged for longer than 1000h. This reactivation is considered as a result of spinodal decomposition of the steel into Cr-rich α′ and Cr-depleted Fe-rich α phases, which has been confirmed by atom-probe and Mössbauer effect. The reactivation peaks in the aged steels may be identified with Fe-rich α-phase with Cr concentration below 12 at%, and 14-20 at%.
