Initiation of stress corrosion cracking in pre-strained austenitic stainless steels exposed to primary water
Résumé
The present study aims at better understanding the role of pre-straining on crack initiation and at developing an engineering model for IGSCC initiation of 304L and 316L stainless steels in primary water. The effects of pre-straining (tensile versus cold rolling), cold-work level and strain path on the SCC mechanisms are investigated. Experimental results demonstrate the predominant effect of the strain path on SCC susceptibility for all pre-straining levels. Maps of SCC initiation susceptibility have been proposed. A critical crack depth between 10 and 20μm has been demonstrated to define transition between slow propagation and fast propagation rate for rolled materials. For tensile pre-straining, the critical crack depth is in the range 20 - 50μm. Experimental evidence supports the notion of a KISCC threshold, whose value depends on materials, pre-straining and applied load. The initiation time has been found to depend on the applied loading as a function of (smax/YS)11.5. In this study, material differences rely on strain path effect on the mechanical properties. As a result, a high stress exponent has been identified which includes all micro-scale mechanisms leading to strain localisation at initiation sites.