Conditions for stress corrosion cracking to occur from crevice corrosion sites and related electrochemical features

摘要

The occurrence of stress corrosion cracking (SCC) from crevice corrosion sites was studied using a kind of occluded U-bend specimen of Type 316L (UNS S31603) stainless steel. It was done in 0.5 M NaCl solution at room temperature and 50℃. The galvano-static and potentiostatic polarization methods were adopted. It was found that a tight crevice and high polarization current were the necessary conditions for SCC to occur relative rapidly from crevice corrosion sites. Meanwhile, if there was obvious SCC developing from a crevice corrosion site, the IR drop (or solution resistance) in the crevice path would increase. The increase of IR was attributed to the corrosion product deposition and/or hydrogen bubbles evolved from the cracks. On the other hand, the usually high aspect ratio of stress corrosion cracks, i.e. the inhibited dissolution on the crack walls, might be explained as due to the existence of high IR drops in them.