The influence of PWHT regime on microstructure and creep rupture behaviour of dissimilar T92/TP316H ferritic/austenitic welded joints with Ni-based filler metal

Abstract

In this paper the dissimilar welded joints between the ferritic (tempered martensitic) steel T92 and the non-stabilised austenitic steel TP316H were investigated in terms of microstructure and creep rupture behaviour characterisation. The welded joints were prepared by the TIG method using the Ni-based filler metal Nirod 600 (Inconel-type). After the welding, the individual weldments were subjected to the two different regimes of post-weld heat treatment (PWHT), either the "classical" PWHT (i.e. subcritical tempering -below Ac1 temperature) or the so-called "full" PWHT including the re-normalisation. The use of "classical" PWHT preserved microstructural gradient in the ferritic steel heat-affected zone (HAZ), which led to a premature creep failure by the "type IV cracking" mode. In contrast, the application of "full" PWHT eliminated the critical HAZ region of T92 steel and changed the creep failure mode to the "interfacial cracking" between the ferritic steel and the Ni-based weld metal. Consequently, this suppression of the "type IV cracking" failure led to a significant creep life increase of the studied ferritic/austenitic welded joints. K e y w o r d s : dissimilar weldment T92/TP316H, post-weld heat treatment (PWHT), microstructure, creep, type IV cracking, interfacial cracking

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

“…2b and 4). Detailed microstructural analysis of Nirod 600 weld metal was performed in our previous studies on T92/TP316H weldments [39,40].…”

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

“…In general, the HAZ region with its strongly heterogeneous microstructure, so-called "HAZ microstructural gradient", is considered to be the critical region of welded joints because of its high propensity for several types of cracking and final failure occurrence [9,10]. The findings of our several former studies about dissimilar T92/TP316H weldments [11][12][13][14] have clearly indicated that the HAZ microstructural heterogeneity can be efficiently suppressed by the application of unconventional "quenching-and-tempering" post-welding heat treatment (QT PWHT). In contrast to microstructural characteristics obtained after conventional "tempering" PWHT (T PWHT), the microstructures of welded base materials after performing QT PWHT became coarser and homogenized with respect to the grain size and state of secondary phase precipitation.…”

Microstructure and properties degradation of P/T 91, 92 steels weldments in creep conditions

“…The same precipitates were indicated in Thermanit Nicro 82 weld metal. Moreover, these precipitates were extracted in carbon replicas and analysed in TEM by SAED technique [15]. It has been confirmed that these precipitates exhibit face-centered cubic crystal structure.…”