EFFECT OF WELDING DILUTION AND DENDRITE ORIENTATION ON SCC BEHAVIOR OF ALLOY 52M WELDING METAL IN SIMULATED PWR PRIMARY WATER

摘要

Due to the complex solidification process after multipassgas tungsten arc welding (GTAW), the transitionregions such as dilution zone, dendritic structure andwelding residual strain/stress zone near fusion boundary(FB) of LAS-nickel base alloy dissimilar weld joint(DMWJ) appeared. SCC behavior in the transitionregions of welding metals shows different trends from thatin base metal. The PWSCC behavior is affected by welddilution and dendrite anisotropy in Alloys 82/182 weldmetals, but there are few data about Alloy 52M. Twodilution zones with concentration gradients are observedin Alloy 52M near the FB. The dendrites in the firstdilution zone show smaller size and higher density thanthose in the second dilution zone. Dendrites in the twodilution zones are perpendicular to the FB. The CTspecimens with notches fabricated parallel to the FB withdifferent distances are used to study the SCCsusceptibility of Alloy 52M dilution zones. The CTspecimens with notches fabricated perpendicular andparallel to the FB are used to study the effect of dendriteorientation on SCC behavior of Alloy 52M in the dilutionzones. PWSCC is found in both the first and the seconddilution zones after the tests in simulated PWR primarywater. Crack growth rate along the dendrite directionwas higher than that across the dendrites.