The Influence of Thermal Exposure and Hydrogen Charging on the Notch Tensile Properties and Fracture Behaviour of Dissimilar T91/TP316H Weldments

Abstract

The effects of ageing and hydrogen charging on the notch tensile properties and fracture behaviour of individual heat-affected zones (HAZ) and Ni-based weld metal (Ni WM) of T91/TP316H weldments were investigated. After the post-weld heat treatment at 750 °C for 1 h the weldments were annealed at 600 °C for 1000 h and 5000 h, respectively. All heat-treated states were studied in condition without as well as with hydrogen charging. Thermal expositions led to additional precipitation and microstructure coarsening but their influence on tensile strength was insignificant. In contrast, remarkable plasticity decrease and the fracture mode transition from ductile dimple tearing to transgranular cleavage were observed. The combined effects of thermal exposure and hydrogen charging were more complex. Whereas the regions of Ni WM and TP316H HAZ did not show any significant change in strength, the hydrogen effect caused the strength increase in T91 HAZ. Although the hydrogen embrittling effects were clearly manifested by decreasing plasticity, their significance was getting smaller with increasing annealing duration. The fracture behaviour of thermally exposed and hydrogen charged regions exhibited mixed fracture modes including transgranular cleavage, intergranular dimple fracture and intergranular decohesion.

Hydrogen pre-charging effects on the notch tensile properties and fracture behaviour of heat-affected zones of thermally aged welds between T24 and T92 creep-resistant steels

“…The additional influence of long-term ageing prior to hydrogen charging of dissimilar ferritic/austenitic weldments on their mechanical and fracture characteristics was studied in [36]. The present work investigates correlations between microstructure, mechanical properties and fracture behaviour of individual HAZ regions of T24/T92 transition weldment in conditions after PWHT and long-term ageing without or with subsequent hydrogen charging.…”

The Effects of Electrochemical Hydrogen Charging on Room-Temperature Tensile Properties of T92/TP316H Dissimilar Weldments in Quenched-and-Tempered and Thermally-Aged Conditions

“…This observation indicated that the influence of hydrogen charging on the plasticity was decreasing with increasing duration of thermal exposure and the dominance of thermal embrittlement was increasing. In addition, it has been concluded that the observed fracture characteristics of individual HAZ regions of T91/TP316H weldment after hydrogen charging corresponded well with their local microstructures and notch tensile properties [26].…”

“…The influence of hydrogen charging on the plasticity of thermally exposed weld regions has varied in dependence of their individual microstructural characteristics and thermal exposure duration. Although the HE effects were clearly manifested by gradual decrease of plastic properties, their differences between the hydrogen-free and hydrogen-charged material states were gradually decreasing with increasing thermal exposure [26,28]. This observation indicated that the influence of hydrogen charging on the plasticity was decreasing with increasing duration of thermal exposure and the dominance of thermal embrittlement was increasing.…”

“…It has been revealed that higher density of fine carbide precipitates in T92 steel microstructure resulted in its higher resistance against HE, compared to T24 steel microstructure containing lower density of coarser precipitates [27,28]. The manifestation of combined effects of thermal exposure and hydrogen charging on tensile properties and fracture behavior of T91/TP316H weldment was more complex than in the case of the effect of pure thermal ageing [26]. The influence of hydrogen charging on the plasticity of thermally exposed weld regions has varied in dependence of their individual microstructural characteristics and thermal exposure duration.…”

“…In our previous studies [25][26][27][28], the effects of electrochemical hydrogen charging on the notch tensile properties and fracture characteristics of individual HAZ regions were investigated for several types of conventionally post-weld heat treated dissimilar weldments between different grades of creep-resistant steels. It has been revealed that higher density of fine carbide precipitates in T92 steel microstructure resulted in its higher resistance against HE, compared to T24 steel microstructure containing lower density of coarser precipitates [27,28].…”