Effect of Tantalum Addition on Crevice Corrosion of Super Duplex Stainless Steels

Abstract

The inclusion control is essential for the development of duplex stainless steels with high local corrosion resistance. In this study, the effect of the inclusion control by Ta addition on the crevice corrosion resistance of the super duplex stainless steels was investigated. The Ta-bearing super duplex stainless steels exhibited the higher crevice corrosion resistance compared to the super duplex stainless steels without Ta. In the super duplex stainless steels without Ta, the dissolution of MnS was observed after the crevice corrosion test, indicating that MnS acts as the initiation of the crevice corrosion. In the Ta-bearing super duplex stainless steels, part of MnS was modified to the (Ta, Mn)-oxysulfide which did not dissolve after the same crevice corrosion test as was conducted for the base alloy without Ta. This demonstrates that (Ta, Mn)-oxysulfide is electrochemically-stable. Thus, Ta addition to the super duplex stainless steel improved the crevice corrosion resistance because of a decrease of MnS which was modified to the electrochemically-stable Ta-containing inclusions.