High Temperature Creep and Fatigue Deformation and Mechanisms of Alloy 800H Weldments Using Different Filler Materials

Abstract

Alloy 800H is one of a few code-qualified materials for fabricating in-core and out-of-core components operating in High Temperature Gas-Cooled Reactors (HTGRs), e.g., reactivity control rods and intermediate heat exchangers. Welding processes will be required for assembly of the reactor components, and the high temperature deformation behaviours of the weldments must be understood because of the heterogeneity in material properties and microstructure between the weld and base metals. At temperatures higher than 400 °C, the high temperature creep rupture resistance of the Alloy 800H weldments significantly decreases when a commonly-used filler material, such as Inconel 82, is used. In this study, alternative filler materials including Haynes 230, Inconel 625, Inconel 617, Inconel 82, and SS 316L were selected to join Alloy 800H using the gas tungsten arc welding (GTAW) technique. High temperature tensile, creep and low cycle fatigue (LCF) tests of the weldments were performed and compared at different stress conditions and strain amplitudes at 760°C. The post-test microstructures were characterized, and the microstructure evolution was analysed. The mechanisms that control the creep and LCF deformation, creep rupture and fatigue life, and associated substructures were investigated.