Stress Corrosion Cracking of Austenitic Stainless Steels under Potentiostatic Polarization

Stress corrosion test under potentiostatic polarization was conducted for the types SUS27 and SUS33 austenitic stainless steels in the Japanese Industrial Standard in 35% MgCl_2 aqueous solution at 100℃. The relationship on the fixed potential between time to failure and applied tensile stress is investigated and obtained results are as follows. 1. Stress corrosion cracking is closely related to the general electro-chemical corrosion property and namely occurs only in the narrow potential range where incomplete passivation can exist. It was found that the potential range for stress corrosion cracking of SUS27 and SUS33 to occur was respectively E=-0.35?-0.41V (3.3N KCI calomel electrode) and E-0.30?-0.36V in the case of constant applied stress, σ=25kg/mm^2 and in the range of more base potential than that, corresponding to passive domain, time to failure increased remarkably. 2. According to the significant decrease of anode current density with time and the behavior of continuous elongation, it may be considered that crack propagates by anodic dissolution at localized active sites. 3. Concerning initiation of cracks, surface of the specimen applied higher stress is corroded widely along slip steps. On the other hand pitting corrosion is often observed under lower stress and the induction period is associated with the time required for effective pit to grow. Therefore, existance of a critical point on stress vs time to failure curves is owing to the difference of mechanisms to initiate origins of cracking.

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