Creep-rupture performance of 0.07C–23Cr–45Ni–6W–Ti,Nb austenitic alloy (HR6W) tubes

A series of base metal and cross-weld creep-rupture tests were conducted on the advanced austenitic alloy, HR6W, to evaluate the material for use at advanced ultrasupercritical (A-USC) steam conditions. Creep deformation and rupture were evaluated by traditional methods and data were compared with other studies to evaluate the creep response of the material. Optical and scanning electron microscopy revealed changes in failure mode and precipitation behavior. Thermodynamic predictions of phase stability were conducted and the results were compared with the experimental data. This research confirmed the important role of W and the precipitation of laves phase in the alloy system, but a direct relationship between laves phase content and creep strength was not observed. Furthermore, Cr content was investigated as an additional factor which may be important in the microstructural stability of the alloy which had not been previously considered. Finally, when compared to commercially available stainless steels, this heat of HR6W showed no creep strength advantage for A-USC application.