Effect of Microstructure and Mechanical Heterogeneity on Mechanical Fields at Stationary and Growing Crack Tips in Dissimilar Metal Welded Joints

Environmentally assisted cracking (EAC) is a slow crack growth phenomenon in dissimilar metal‐welded joints within the primary circuit of pressurized water reactors. Accurately analyzing the mechanical state at the EAC tip is crucial for ensuring the long‐term safety of nuclear power equipment. In this study, microstructure analysis of the SA508‐52M‐316L welded joint was conducted to determine the distribution of mechanical properties in its local regions through hardness testing. A user‐defined field subroutine (USDFLD) is developed to accurately characterize the mechanical heterogeneity of these regions. The effect of mechanical heterogeneity on the mechanical fields at stationary and propagating crack tips in the interface region is investigated. The results show that mechanical heterogeneity primarily originates from the microstructure of the local regions of the welded joint. Significant changes in mechanical properties are often observed at material interfaces, making these regions particularly vulnerable to damage. Under the same loading conditions, mechanical heterogeneity significantly influences the initial mechanical fields. The mechanical field at the crack tip redistributes during crack growth, and significant residual deformation is observed along the crack growth path. To ensure a reliable integrity assessment of nonhomogeneous welded joints, it is recommended to use material properties specific to the crack location.