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

Abstract

The effects of thermal exposure at 600• C and subsequent electrolytic hydrogen charging at ambient temperature were studied in terms of their influence on notch-tensile properties and fracture behaviour of individual heat-affected zones (HAZ) of Ni-based transition weldments between T24 and T92 creep-resistant steels. The experimental welded joints were prepared by gas tungsten arc welding using "Inconel-type" filler metal Nirod 600. Post-weld heat treatment (PWHT) was carried out at 720• C for 2 h, followed by passive cooling within tempering furnace. Subsequent long-term ageing of two series of prepared T24/T92 dissimilar welds at 600• C for 1000 and 5000 h, respectively, led to gradual changes in both T24 and T92 HAZ microstructures, which were mainly related to their additional tempering accompanied by the coarsening of original precipitates as well as newly-formed secondary phases. The observed thermally-induced microstructural changes together with subsequently applied hydrogen charging effects resulted in complex variations in tensile properties and fracture behaviour of individual HAZ regions related to the pre-existing differences in their initial tempering grade due to the used PWHT procedure. K e y w o r d s : creep-resistant steels, dissimilar welding, isothermal ageing, hydrogen embrittlement, mechanical properties, fracture mechanisms

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

“…The value of embrittlement index is higher in the former case than in the latter. These findings are consistent with the previous findings by Falat et al [26][27][28]. In the initial state, the hydrogen embrittlement plays the dominant role.…”

“…Due to additional precipitation of carbides and/or their coarsening during thermal exposure, the number of irreversible hydrogen traps is increased and by this way the volume of free mobile hydrogen is decreased [17]. Because only diffusible hydrogen plays a role in the hydrogen embrittlement [52,53], the performed thermal aging has led to decreased measure of hydrogen embrittlement and the dominance of thermal embrittlement [26,27]. The details on the fracture behavior of the studied weldments will be discussed in the following section.…”

“…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]. 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 microstructure on hydrogen diffusion and embrittlement of fine-grained high strength dual-phase steels

“…However, in the case of combined thermal and hydrogen embrittlement effects, the situation is much more complicated. There are plenty of different microstructural sites in steels, such as grain boundaries, free dislocations, precipitates, and inclusions that may interact with absorbed hydrogen and affect the resulting ten- sile properties and fracture behaviour [26].…”

The Effects of Electrochemical Hydrogen Charging on Charpy Impact Toughness and Dry Sliding Tribological Behavior of AISI 316H Stainless Steel

“…In our previously published works [19][20][21][22][23][24], we investigated the effects of various conditions of heat treatment, including long-term isothermal expositions and the electrolytic hydrogen charging of welded joints of advanced creep-resistant steels on their mechanical and brittle-fracture properties. In these complex material systems, certain small improvements in HE resistance were observed after laboratory high-temperature aging experiments, which could be explained by internal stress relieving as well as by the additional precipitation of fine carbide particles leading to irreversible hydrogen trapping at carbide/matrix interfaces [19][20][21][22][23][24]. However, at the same time, the gradual development of thermal embrittlement was clearly observed due to the precipitate coarsening of several secondary phases (e.g., special alloy carbides and intermetallic phases) with the increasing duration of thermal exposure.…”