Abstract
The corrosion behavior of metal is closely related with its polarization behavior in a corrosive solution. The polarization behavior is also useful for understanding pitting corrosion or stress corrosion cracking in particular. Stainless steel was adopted as the testing material in this experiment and the anodic polarization curves were measured under various constant loads applied on the specimen in 3% NaCl solution, and the pitting initiation potential, passivity, passivity maintaining current, the change in roughness of specimen surface and the difference in pitting corrosion depth were also measured. The results obtained are as follows.
(1) The pitting initiation of SUS 430 was less noble than SUS 316 and the pitting initiation potential shifted towards the less-noble side with increasing applied stress. Under no stress condition, the pitting initiation potential of SUS 316 was about +0.20V(vs. S.C.E.), and SUS 430 about 0.00V(vs. S.C.E.), but they began to shift remarkably towards the less-noble side from the yield point of the specimen. In the plastic deformation region, the pitting initiation potential of SUS 316 and SUS 430 became -0.0058V and -0.30V, respectively. Therefore, a part of the safe potential region for corrosion under no stress was changed to the pitting initiation potential region by the increase in applied stress.
(2) The passivity maintaining current increased with increasing applied stress. The pits in SUS 430 grew to deep pits and concentrated on the specified area of specimen surface. On the other hand the pits depth in SUS 316 was shallow and were dispersed over the specimen surface.
