Three-dimensional imagination and composition analysis of welding defects in dissimilar metal weld joint of third generation domestic nuclear power plant by high resolution transmission X-ray tomography

The microscopic welding defects in dissimilar metal weld joint of third generation domestic nuclear power plant were studied by high resolution transmission X-ray tomography and OM and SEM, and the distribution and size and morphology and micro-area composition of welding defects were characterized within this study. The conclusions indicate that the main defects are hot welding cracks, and they are located in dendrite grain boundaries of nickel-base alloy 690 weld, and these dendrite grain boundaries are adjacent to alloy 690 weld buttering. The cracks are mostly large-size irregular flake-like voids which distributed in parallel groups along facets of dendrite grains. The thickness of these cracks is about 20-50 μm, and the maximum crack length is up to l mm. The precipitates concentrated with Nb and Ti were discovered on the inner surface and around the crack. The toughness tear fracture and eutectic melting were observed within the inner surface of welding crack. (authors)