The in-situ observation of preferential dissolution behaviour on crevice corrosion of a duplex stainless steel

The purpose in this study is to clarify preferential dissolution behaviour on crevice corrosion of a duplex stainless steel by means of an in-situ observation with an optical microscope and a transparent cell. The metal specimen (UNS S31260) / poly methyl methacrylate (PMMA) artificial crevice was prepared by using a transparent PMMA cell wall with Ti bolt, nut, and washer. Thus, micro dissolution behaviour of crevice corrosion on the specimen surface could be observed in-situ by means of an optical microscope. The crevice corrosion initiated just beneath the edge of PMMA washer, it grew toward the edge of the crevice with time. In the corrosion area, at first, austenitic phase dissolved preferentially, and then ferritic phase of this area started dissolving with corrosion area extending. Finally, ferritic phase dissolved preferentially at that area. Four types of dissolution regions could be observed in the corrosion area from the outside toward inside direction; they were passive region, the preferential dissolution region of austenitic phase, both phase dissolution region, and the preferential dissolution region of ferritic phase. Based on the our previous reports of the relationship between the polarization behaviour and the preferential dissolution phase of the DSS in simulated solution inside corroding crevice, change with time of the preferential dissolution behaviour in this study was described.