Under-deposit chloride-induced stress corrosion cracking in austenitic stainless steels: Aspects associated with deposit type, size and composition

摘要

The occurrence of Atmospheric chloride-Induced Stress Corrosion Cracking (AISCC) in austenitic stainless steels beneath 'wetted' deposits of either artificial sea-salt, organically-enriched artificial sea-salt or MgCl 2.6H2O has been investigated under controlled climatic conditions (40°C and 33% relative humidity). The presence of organic exudate in relatively large artificial sea-salt deposits (~3 mm diameter) appears to markedly decrease the induction time associated with AISCC; cracking occurred within a week in one U-bend specimen, well inside the ~12 week period usually observed under 'wetted' deposits of artificial sea-salt alone. Cracks appear to initiate from crevices formed under NaCl crystals. It is tentatively proposed that the organic species promotes greater coverage by the MgCl2 electrolyte in the vicinity of these crystals. This increases the probability of crevice initiation, and allows more rapid production of localized corrosion sites (pits or crevices) propagating under conditions that allow the transition to AISCC (pit/crevice dissolution rate crack velocity). © 2014 The Electrochemical Society.