Effect of Mechanical Heterogeneity on Creep and Stress Corrosion Cracking Propagation in Nuclear Safe-End Dissimilar Metal Welded Joints

The dissimilar metal welded joints at the safe ends of nuclear primary circuits are highly susceptible to stress corrosion cracking (SCC) initiation in high-temperature, high-pressure water environments. Existing predictive models are predominantly based on homogeneous material assumptions, making it challenging to accurately evaluate the actual failure behavior of welds caused by mechanical property heterogeneity. Consequently, based on the mechanical gradient obtained from hardness tests, this study constructs a finite element model with continuously varying mechanical properties to quantitatively investigate SCC behavior under different crack characteristics. The analysis demonstrates that mechanical heterogeneity significantly influences the crack tip mechanical fields: When the crack is located proximal to the sub-interface (d = 1 mm), the severe mechanical mismatch induces a sharp increase in creep strain, resulting in a peak SCC propagation rate approximately 14.6% higher than those at d = 3 mm. Furthermore, extending the crack length at the weld center (a/W from 0.45 to 0.60) expands the plastic strain zone along the propagation direction, driving an approximately 43.6% increase in the crack growth rate. The heterogeneous model, accounting for the local mechanical gradient, can more accurately reveal the influence laws of crack position and length on SCC propagation behavior, providing theoretical support for improving life prediction accuracy and in-service inspections.