Long-Term Behavior of Welded Connections of Martensitic/Bainitic Steels and Nickel-Based Alloys Under Near-to-Service Loading

Abstract The paper aims to experimentally investigate the long-term behavior of welded connections between nickel-based alloys and martensitic/bainitic steels. It specifically examines the creep and thermo-mechanical fatigue performance at a maximum temperature of 625 °C using membrane test panels. Numerical simulations are employed to estimate testing parameters that induce significant damage during the experiments. Metallographic analysis of the circumferential welds between T24/A617B and HR6W, as well as T92/A617B and HR6W, revealed no damage related to the tests. However, small cracks behind the heat-affected zone in the fin welds of the T24 panel led to its failure after reaching 3% local creep strain, with the damage mechanism identified as typical creep damage. Overall, the long-term creep strain was reasonably well predicted by finite element (FE) analysis. However, further optimization of the material parameters for the creep model is needed to improve the accuracy of the creep strain prediction.