Microstructure of Heat-Affected Zone in a Weld Joint between Alloy 690 and Alloy 152

The distributions of residual strains, micro-hardness, intra-grain average misorientation（GAM）, grain boundary microstructure and metallurgical characteristics were investigated at the top, middle and root of the heat-affected zone of a weld joint between pressurized water reactor（PWR） control rod drive mechanism（CRDM） Nozzle Alloy 690 and Alloy 152 using electron backscatter diffraction（EBSD）, scanning electron microscopy（SEM） and micro-hardness tester. The results showed that the residual strain decreased from the last welding top of the weld to root, the maximum residual strain is 5.15% at the top of the last weld; the average fraction of coincident site lattice ∑3 special boundaries increased from the last welding top of the weld to root, the minimum fraction of ∑3 special boundaries is 46.6%, which is remarkably less than that 68% of the base 690 alloy. The HAZ at the top of the weld is considered to sustain the highest stress corrosion cracking（SCC） susceptibility.