Pit Formation in Stainless Steel under Applied Stress with or without Chamfering

Abstract

Pitting corrosion, which affects the fracture of stainless steel in corrosive environments, is an electrochemical phenomenon. There are still many unanswered questions with respect to the pitting corrosion and, furthermore, there is no well-established inhibition method for the pitting corrosion at present. Stainless steel was adopted as the testing material in this experiment, and the state of formed pits was examined on the rectangle section specimen and the chamfering specimen in deaerated 3%NaCl solution under various constant loads by changing the holding time of pitting potential which was determined from the anodic polarization curve. The results obtained are as follows.
(1) The formation of pits proceeded gradually and led to deep pits with increasing holding time of pitting potential, and it was expressible as a function of time. The process of deep pit formation differed from SUS 304 and SUS 430. The pitting formation was promoted and accelerated by the presence of stress. Deeper pits were formed under the applied stress above the yield point in particular and this phenomenon became more pronounced at high setting potentials.
(2) The number of pits changed with increasing holding time of pitting potential and applied stress. The appearance of pitting corrosion on SUS 304 was different from that on SUS 430. The pits on SUS 304 were distributed all over the specimen surface, and they were numerous and shallow. But the pits on SUS 430 were localized in a certain area of specimen surface, and they were small in number and deep.
(3) The chamfering specimen had a tendency to inhibit the pitting formation to a certain extent. In addition, the surface condition (roughness) seemed to be the major factor on the pitting formation.