GALVANIC EFFECTS ON THE ACTIVE DISSOLUTION OF DUPLEX STAINLESS-STEELS

This investigation concerned the active dissolution of a duplex stainless steel in two different acidic solutions together with a comparison of the active dissolution of the corresponding α-and γ-phases in order to establish the type of interaction between the phases. In the two acid solutions investigated, galvanic action between the two phases took place, although leading to different types of dissolution. Some other features of the active dissolution of duplex steels, such as the time dependence of the anodic current, the influence of surface morphology, surface area ratio, etc. are also discussed. The procedure chosen is based on a comparison of the corrosion properties between a duplex steel, SAF 2205 (UNS S31803) and two special alloys having compositions similar to the α- and γ-phases of the duplex steel. Comparison is also made between the austenitic special alloy and 316L (UNS S31603) as well as between SAF 2205 and 3xRE68, which is also a duplex steel. The solutions used were 2 M H2SO4 + 0.1 M HCl and 2 M H2SO4 + 2 M HCl.