New insight into high-temperature creep deformation and fracture of T92 steel involving precipitates, dislocations and nanovoids

T92 steel is one of the most important heat-resistant materials for power plant steam tubes. In the present study, precipitates are found to be strongly associated with creep deformation and crack initiation of T92 steel at high temperature. Using TEM imaging and in-situ tensile stress testing, we show that MX precipitates have excellent resistance to dislocation cutting during creep, while M23C6 and Laves phase precipitates are prone to cutting by dislocation glide, which provides a dislocation slipping path. Importantly, crack formation is observed to initiate in the cut M23C6 and Laves phase precipitates. At the crack tip, nanovoids tend to move toward plastic strain zones (PSZ's) during tensile stress testing, and crack propagation in matrix occurs as a coalescence of the PSZ with the nanovoid. Possible mechanisms to explain these observations are also discussed. (C) 2017 Elsevier Inc. All rights reserved.