Transgranular stress-corrosion mechanisms

Defect oxide formation means poor repassivation behaviour and supports the film rupture mechanism for transgranular stress corrosion cracking which has been observed on solution annealed steels in high purity water, particularly at low oxygen contents. 

N Winzer, A Atrens, W Dietzel, G Song, KU Kainer, Evaluation of the delayed hydride cracki ng mechanism for transgranular stress corrosion cracking of magnesium alloys. Materials Science and Engineering A, 2007, 466, 18-31. 

Stress corrosion cracking (SCC) is a special corrosion form, which is seen as fine-branched transgranular cracks in the material. SCC is caused by a combination of mechanical stress, the presence of chlorides and elevated temperature. At high temperature and high mechanical stress. SCC of 316-type stainless steel can occur at chloride levels even below 1000 ppm. The answer to this is to use a more corrosion-resistant stainless steel or a duplex stainless steel. Duplex stainless steels normally do not show SCC at temperatures below 100°C. 

Even with alloying additions such as molybdenum to improve localized corrosion resistance to halogens, the workhorse 304 and 316 alloys are susceptible to chloride stress corrosion cracking (SCC). This cracking mechanism manifests itself as branched, generally transgranular cracks that are so fine as to be virtually imdetectable until it has progressed to catastrophic proportions. This mode of failure can occur when the austenitic alloy is under... 

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