Effect of microstructure of weld metal on SCC crack growth behavior near fusion line in low carbon stainless steel weld joints

SCC growth tests on the specimens machined out from a type 316NG pipe weld joint and type 316L hot rolled plate weld joints were conducted in simulated BWR coolant condition to clarify SCC growth behavior near weld fusion line and effects of microstructure of weld metals on SCC growth behavior. The results obtained are follows; (1) IGSCCs from pre-crack tips in base metal propagated toward the weld metal with branching of secondary cracks, and then, the cracks changed direction to avoid the weld metal and propagated along with the fusion line. (2) Results of crack length measurements for the cracks, which propagated into weld metal showed that more than 80% of cracks located within 50 μm from the fusion line. (3) Geometrical continuity between austenite grain boundary and dendrite boundary at the fusion line is dominant to SCC growth behaviors into the weld metal. All of the cracks which propagated into weld metal more than 50 μm were only observed in the dendrite boundary with high geometrical continuity between austenite grain boundary and dendrite boundary at the fusion line. (author)