STRESS CORROSION CRACKING ON COLD-WORKED AUSTENITIC STAINLESS STEELS IN PWR ENVIRONMENT

Types 304L and 316L austenitic Stainless Steels (SS) are widely used in PWR environment. These past few years, a limited number of cases of intergranular stress corrosion cracking (IGSCC) have been detected in cold worked areas of non sensitized austenitic stainless steel components. A first study has been initiated at EDF to assess the conditions of the cracking. The main results include cold work thresholds of 240 HV0,1 for initiation cracking, and of 310 HV0,1 for crack propagation, and propose that a dynamic loading is necessary for SCC. The aim of the present paper is to provide a basis of a crack propagation model by investigating the effect of loading, material and cold-work. In order to try to approach a static loading, a trapezoidal cyclic loading is applied on high cold-worked (by rolling or by tensile loading) materials. It is shown that, for the most severe loading, the rolling cold-worked (RCW) materials undergo TGSCC whereas IGSCC is observed after tensile cold-working (TCW). The ratio of loading R has such a strong impact on the crack growth rate (CGR) that it modifies the mechanism of cracking. Moreover, we notice that CGR increases with the applied Kmax but this evolution depends on the R value. Therefore, ∆K is chosen to represent the mechanical loading effects on CGRs. Finally, the CGR after a hold time of 1 hour is quite the same than for 3 hours. Additionally, to address the critical issue of the effect of the crack tip strain rate on crack growth rate, Slow Strain Rate Tests (SSTR) are carried out on RCW specimens and provide a first relation which is not consistent to a pure anodic process. This study is going on TCW specimen