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.

Key words
dissimilar weldment T92/TP316H, post-weld heat treatment (PWHT), microstructure, creep, type IV cracking, interfacial cracking

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