Effect of Crack Location on the Mechanical State at the Tip of Stress Corrosion Cracks in Dissimilar Metal Welded Joints

Abstract

Dissimilar metal weld joints (DMWJs) between low-alloy steel SA508 and austenitic stainless steel 316L, fabricated using nickel-based alloy 52M as filler metal, are critically important in the primary circuit of pressurized water reactors (PWRs). The structural integrity of such DMWJs is strongly influenced by the mechanical heterogeneity, especially near the fusion line (FL). In this study, the local mechanical properties of an SA508-52M-316L DMWJ were determined via an indentation test, while metallographic analysis was employed to characterize the heterogeneous microstructure adjacent to the FL. A finite element (FE) model incorporating continuously graded mechanical properties was developed using a predefined temperature field approach to represent the material heterogeneity more accurately than conventional sandwich models. Based on this continuous transition model, elastoplastic FE analyses were conducted to evaluate the Mises stress and plastic strain distributions at the tip of cracks located at different positions relative to the FL. The results reveal that the inhomogeneous mechanical property distribution significantly alters the crack-driving force, particularly when the crack approaches the FL region, underscoring the necessity of accounting for local heterogeneity in the structural integrity assessment of DMWJs.