The influence of hydrogen charging on the notch tensile properties and fracture behaviour of dissimilar weld joints of advanced Cr–Mo–V and Cr–Ni–Mo creep-resistant steels

The influence of hydrogen charging on the room-temperature tensile properties and fracture behaviour of two dissimilar weld joints has been investigated. The weld joints were either ferritic/ferritic (T91/STN15128) or ferritic/austenitic (T91/TP316H). The tensile tests were carried out using the samples with a circumferential notch. The position of notch was individually located in different weld joint regions, either in the heat-affected zones (HAZ) or weld metal (WM). The application of hydrogen charging had detrimental effect on strength and plasticity of the weld joint T91/STN15128. The most significant deterioration of the notch tensile properties was measured for the STN15128 HAZ. The hydrogen charging had only small influence on the strength of the weld joint T91/TP316H but remarkable detrimental effects on the plasticity. In the PWHT state (without hydrogen charging) all regions of the studied weld joints fractured by ductile dimple tearing. The failure initiated on the secondary phase particles and/or inclusions as well. In contrast, the failure after hydrogen charging initiated in the vicinity of sizeable particles and showed a transition from the ductile dimple tearing to the transgranular cleavage and/or quasi-cleavage fracture mode.