Microstructural evolution of P92 steel in IN740H/P92 dissimilar weld joints during creep deformation

Abstract

In this study, we report the microstructural development of heat-affected zone in P92 heat-resistant steel during creep deformation in cross-weld specimens with dissimilar weld joints between IN740H/P92 materials. Different specimens were prepared via the interruption of creep testing at 50, 70, and 90% of the measured creep-rupture life and were carefully examined and compared. To explain the deformation behavior, finite element analysis was performed in conjunction with softening behavior measured by electron back-scattered diffraction and hardness mapping. The FGHAZ II region defined in this study could be related to the generally known intercritical heat-affected zone, which showed major changes in microstructure during creep deformation due to the accelerated softening by dynamic recrystallization as well as to the development of a triaxial stress state. As a result, cavity formation and growth was observed only in the FGHAZ II region, which ultimately led to fracture.