Abstract
The influence of isothermal aging at 620 °C in combination with subsequent electrochemical hydrogen charging at room-temperature was studied on quenched-and-tempered T92/TP316H martensitic/austenitic weldments in terms of their room-temperature tensile properties and fracture behavior. Hydrogen charging of the weldments did not significantly affect their strength properties; however, it resulted in considerable deterioration of their plastic properties along with significant impact on their fracture characteristics and failure localization. The hydrogen embrittlement plays a dominant role in degradation of the plastic properties of the weldments already in their initial material state, i.e., before thermal aging. After thermal aging and subsequent hydrogen charging, mutual superposition of thermal and hydrogen embrittlement phenomena had led to clearly observable effects on the welds deformation and fracture processes. The measure of hydrogen embrittlement was clearly lowered for thermally aged material state, since the contribution of thermal embrittlement to overall degradation of the weldments has dominated. The majority of failures of the weldments after hydrogen charging occurred in the vicinity of T92 BM/Ni weld metal (WM) fusion zone; mostly along the Type-II boundary in Ni-based weld metal. Thus, regardless of aging exposure, the most critical failure regions of the investigated weldments after hydrogen charging and tensile straining at room temperature are the T92 BM/Ni WM fusion boundary and Type-II boundary acting like preferential microstructural sites for hydrogen embrittling effects accumulation.
Highlights
In several last decades, demands for higher efficiency and lower environmental pollution in electricity generation, have led to the development of so-called “ultra-supercritical” (USC) power plant boiler technology using as a working medium supercritically heated and pressurized steam with temperature of 620 ◦ C and pressure of 25 MPa and above [1,2,3]
The individual microstructural regions of investigated T92/TP316H dissimilar weldment, namely same phase composition was base alsomaterial observed in base material (BM)), otherNi-based studies weld on similar types of Thermanit
Quenched-and-tempered T92/TP316H martensitic/austenitic dissimilar weldments with Ni-based weld metal (Thermanit Nicro 82) were isothermally aged at 620 ◦ C for 2500 h and electrochemically hydrogen charged in order to investigate the effects of hydrogen charging on room-temperature tensile properties
Summary
Demands for higher efficiency and lower environmental pollution in electricity generation, have led to the development of so-called “ultra-supercritical” (USC) power plant boiler technology using as a working medium supercritically heated and pressurized steam with temperature of 620 ◦ C and pressure of 25 MPa and above [1,2,3]. Apart from thermal and mechanical loading, inner parts of power plant boiler tubing and/or piping may operate in hydrogen containing environments since the used working medium can be a source of free atomic hydrogen It is well-known that mechanical properties of metallic materials can be significantly affected by absorbed hydrogen in their microstructures containing several specific microstructural constituents such as free dislocations, grain/subgrain boundaries, precipitates and inclusions which may act like either reversible or irreversible hydrogen traps [15,16,17,18]. 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. The observed hydrogen-induced changes in mechanical properties and fracture behavior of the investigated weldments are characterized and discussed
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