Abstract
Creviced SSRT tests were conducted on low carbon austenitic stainless steels and their weld metals in a simulated BWR environment. When the materials were non-sensitized, the most of SCC is recognized TGSCC. From the SEM observation at high magnification indicated the presence of micro-cracks whose length is less than 5μm in all cases. TEM observation of micro-cracks shows us the Cr-rich point at the non-propagating crack tip. Examination was made of the effects of the exposure time prior to loading, applied strain, cold work, DO level, chemical compositions of base materials and volume fraction of ferrite in weld metals obtained from creviced SSRT. At less than 20% of rolling reduction, no effects of cold work could be seen, but at 30% of rolling reduction, high SCC susceptibility was apparent. A comparison of SCC susceptibility for type 304NG and 316NG indicated fewer cracks in the type 304NG. Thus possibly, Cr contents or the sub-structure may be related to SCC initiation. In weld metals, SCC occurs in the austenite phase or at the interface between austenite and ferrite. Weld metal with medium amount of ferrite has been shown to exhibit high SCC resistance since the ferrite network fuctions to be an obstacle for crack propagation.
