Dissolution Mechanism of Duplex Stainless Steels in the Active-to-Passive Transition Range and the Role of Microstructure

A new aspect of the special corrosion behavior of duplex stainless steels (DSS) in acid solutions was investigated. Combined examination of the current oscillations observed in the potential range of the active-to-passive transition, together with metallographic examination of the surface morphology of the exposed material, showed the oscillations arose from preferential dissolution of one of the phases and the subsequent formation of cavities. In this respect, acid corrosion of DSS resembles localized corrosion. When all other parameters are constant, the geometric characteristics of the microstructure determine the corrosion behavior of the duplex material.