Effect of applied stress on the initiation and propagation behavior of SCC for sensitized 304 stainless steel under MgC12 solution droplet

摘要

Austenitic stainless steels have been widely used in various engineering fields due to their excellent weldability, superior anticorrosion properties, and so on. However, austenitic stainless steels can suffer from localized corrosion in chloride-containing environments. Especially in atmospheric environments, thin water-layer film containing high concentration of chloride ions can be formed and initiation and propagation of localized corrosion can be accelerated. In addition, local corrosion sites such as pits can become initiation sites for stress corrosion cracking (SCC) when the steels are subjected to tensile stress. Therefore, SCC in austenitic stainless steels can take place readily especially in atmospheric corrosion environments. In this study, initiation and propagation behavior of SCC for sensitized 304 stainless steel under a MgC12 solution droplet was investigated by 4-point bending tests. We focused on the effect of applied stress on SCC behavior for the steels. It was found that pit initiation was not enhanced regardless of the magnitude of applied stress. On the other hand, morphology of pitting corrosion clearly showed dependency on the thickness of a solution layer. Under a thin solution layer, cracks were initiated by applying plastic deformation. By contrast, in case of a thick solution layer, the propagation of cracks was not accelerated very much, even by applying plastic deformation. In the presentation, SCC mechanism in the steels will be discussed.