1992 Volume 41 Issue 10 Pages 670-676
The intergranular corrosion of nonsensitized SUS 304 and SUS 316L steels was investigated in a 1Kmol·m-3 oxalic acid solution by means of Inductively Coupled Plasma Emission Spectrometry (ICP) and Scanning Electron Micrography (SEM). It was found that on the both steels, the ditch structure was observed in the transpassive potential below 1.3V (SCE), and the step structure was observed above 1.3V (SCE). The result in the compositions of dissolved metal ions was that the preferential dissolution of P and Si occurred in the transpassive potential below 1.3V (SCE). Furthermore, it was found that above 1.3V (SCE), the amount of oxygen evolution increased. Deduced from the obtained results, dissolution of P and Si which were segregated at intergranular was prior to all other elements, above the break-through potential (about 0.9V). As a result of that, intergranular corrosion occurred. Between 1.0V and 1.1V (SCE), oxygen evolution started, which mainly took place at segregated grain boundary. Amount of oxygen evolution was increased by anodic polarization. That caused susceptibility of intergranular corrosion gradually small. And above 1.3V (SCE), oxygen evolution took place in grain and grain boundary, so that nonsensitized austenitic stainless steels were not susceptible to intergranular corrosion.