Mechanism of Intergranular Corrosion of Austenitic Stainless Steels—Literature Review

The literature on intergranular corrosion of austenitic stainless steels is reviewed, with particular reference to the theories of intergranular corrosion and the connexion between carbide morphology and the corrosion susceptibility. In the Strauss solution, intergranular corrosion is due to the formation of a chromium-depleted region adjacent to a continuous grain boundary carbide. In a strongly oxidising atmosphere, such as nitric acid contaminated with Cr6+ ions, the chromium-depleted layer appears to have little effect on the corrosion sensitivity and corrosion proceeds by transpassivity. The healing effect is associated with the formation of discontinuous carbides, a finding which is compatible with all the theories of intergranular corrosion. However, an investigation is to be carried out to examine more closely the relationship between the carbide morphology and intergranular corrosion susceptibility.