Environmentally assisted cracking behavior of dissimilar metal weldments in simulated BWR coolant environments

The environmentally assisted cracking behavior of dissimilar metal (DM) welds, including Alloy 52-A 508 and Alloy 82-A508, under simulated BWR coolant conditions was studied. Effects of postweld heat treatment and sulfur content of the base metal on the corrosion fatigue and SCC growth rates of DM welds were evaluated. The crack growth rates for the DM weld heat-treated at 621°C for 24h were observed to be faster than those for the as-welded. But the DM weld heat-treated at 621°C for 8h+400°C for 200h showed better SCC resistance than the as-welded. The longer the heat treatment at 621°C, the higher the chromium carbides density along the grain boundary was observed. Sulfur could diffuse out of the base metal and segregate along the grain boundaries of the dilution zone, leading to weakening the grain boundary strength and the SCC resistance of the Alloy 52-A508 weld.