2016 Volume 65 Issue 12 Pages 498-504
The electrochemical tests instead of the immersion tests for evaluating a crevice corrosion resistance of stainless steel are used. One of the electrochemical tests is the test method of JIS G 0592 that is the cyclic polarization test with the stepwise potential backscan. However, the propagation behavior of crevice corrosion during this test is unclear enough; e.g., the corrosion behavior in crevice at each step (step I-step IV) of the test procedure or under the potential of the critical potential, E'R,CREV, determined by JIS G 0592. When the corrosion depth of the specimen after the test is more than 40μm, E'R,CREV is renamed ER,CREV, the repassivation potential.
In this paper, in-situ observation of the crevice corrosion propagation behavior in the quartz-glass/metal crevice of SUS 304 and SUS316L was carried out at each step of the test procedure from step I to step IV. Main results were as follows;
(1) A crevice corrosion occurred at the step I, potentiodynamic stage, and the early stage of step II, galvanostatic stage. The crevice corrosion spread in the crevice and penetrated into the depth at the edge of crevice mouth until the end of step II.
(2) The crevice corrosion propagated as increasing in corroded area at step III, potentiodynamic backscan stage, and at step IV, stepwise potential backscan stage. Furthermore, the crevice corrosion area continuously increased even under the potential of E'R,CREV determined at stage IV. The propagation of crevice corrosion stopped under the potential at which there was no expansion in corroded area.