Stress corrosion cracking on cold-worked austenitic stainless steels in PWR environment

Over the few years, limited cases of IGSCC have been detected in cold-worked areas of non-sensitized austenitic stainless steel components of French PWRs. Our first study of this phenomenon determined the required conditions for SCC of 304L in the laboratory after brief exposures to the PWR primary water environment : cold-work to a hardness > 240 HV0,1 for true initiation and > 310 HV0,1 for propagation, and dynamic loading. A SCC propagation model is developed here by investigating the effect of periodic and partial unloading/reloading, material properties (304L vs 316L) and cold-work (rolling (RCW) vs tensile (TCW) cold-work). It is shown that RCW materials undergo TGSCC or IGSCC and TCW materials IGSCC. The loading ratio R modifies the mechanism of the cracking and seems to decrease the stress intensity factor threshold (KISCC). No obvious effect of the hold time is observed on the crack growth rate but the initiation time depends on the hold time. (author)