Corrosion Behavior of a Duplex Stainless Steel in a Simulated Crevice Solution

The repassivation potential of corroding crevices of a duplex stainless steel was measured in a deaerated 3.5mass% NaCl solution according to JIS G 0592.  The change of current density with time and preferential dissolution phase during anodic polarization in -370mV to +150mV (vs. SCE) potential region in a simulated crevice solution (25mass% NaCl, pH=0) were investigated.  The repassivation potential of crevice corrosion depended on the holding potential and time for ensuring the propagation of crevice corrosion, and in the all cases, the preferential dissolution of ferrite phase was observed.  The current density was rather steady during the polarization in the active peak region (-370mV to -260mV).  While, it decreased with time in the active-passive transition region (-200mV to -150mV).  In the passive region (0mV to +150mV), it first decreased, and then increased gradually.  On the less-noble side of the active peak region, preferential dissolution occurred on the ferrite phase.  On the other hand, on the noble side of the active peak region and in the active-passive transition region, it occurred on the austenite phase.  In the passive region, the both phases dissolved evenly.  These results suggest that the potential in the crevice drops to the less-noble side of the active peak region by the IR drop mechanism.