STRESS CORROSION CRACKING BEHAVIOR OF DISSIMILAR METAL WELDMENTS IN HIGH TEMPERATURE WATER ENVIRONMENTS

摘要

The stress corrosion cracking behavior of dissimilar metal (DM) welds, including Alloy 52-A 508 and Alloy 82-A 508, under simulated BWR coolant conditions was studied. Effects of postweld heat treatment and specimen size on the corrosion fatigue and SCC growth rates of DM welds were evaluated. The crack growth rates of the DM weld heat-treated at 621 °C for 24 h was observed to be faster than those for the as-welded. But the DM weld heat-treated at 621 °C for 8 h + 400 °C for 200 h 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. The SCC growth rates observed for the 1/2T CT specimens were faster than those for IT CT specimens. It could be accounted for by the shorter distance for oxygen and anions to diffuse to the crack tip in the thinner specimen.