Residual strain measurement and grain boundary characterization in the heat-affected zone of a weld joint between Alloy 690TT and Alloy 52

The distributions of residual strains and grain boundary microstructures were investigated in the heat-affected zone (HAZ) of a weld joint between Alloy 690TT (thermally treated) and Alloy 52 using electron backscatter diffraction (EBSD) and transmission electron microscopy. The distributions of residual strains were examined at the top, middle, and root of the HAZ using EBSD to obtain the grain average misorientation. The weld residual strain increased from the top of the weld to the root while the peak of strain approached the fusion boundary (FB) in the HAZ. The maximum strains and their distances to the FB in the top, middle, and root was 15% and 800 μm, 17% and 600 μm, 20% and 200 μm, respectively. The fraction of Σ3 special boundaries was about 40% in the HAZ but with obvious deviations from the structure of ideal boundaries. The HAZ region is considered to sustain the highest susceptibility to SCC at the root of the weld.