Advanced Assessment of Ductile Fracture Behaviour in Dissimilar Metal Welds Using X-Ray Tomography

Dissimilar metal welds represent a challenge for structural integrity assessments of nuclear plants due to the complex microstructure and variation in properties over short length scales. This paper presents the findings of a study aimed at investigating the fracture behaviour of a dissimilar metal weld of SA508-4N steel joined to 316LN stainless steel via a filler weld of Alloy 82. Fracture toughness observations have shown the crack growth direction extended from the SA508-4N heat affected zone into the Alloy 82 weld metal. Finite element modelling has been used to simulate the fracture toughness testing with the crack-tip positioned in different material regions. The results have shown that the location of the crack-tip in relation to the fusion boundary and material properties being sampled by the plastic zone has a significant effect on the fracture behaviour of the dissimilar metal weld. Finally X-ray tomography of tested material has provided significant insights into the level of initial porosity within the dissimilar metal weld and development of ductile damage in the materials surrounding the crack-tip. This has been used to infer parameters for a continuum ductile damage model that is used to simulate crack growth.