Fig. 1 Optical microstructure of the as-received annealed specimen

Fig. 2 Microstructures of the specimen after creep deformation at 973 K and 50 MPa: a SEM image of the precipitates, and the insets show the typical precipitates and corresponding EDS results; b TEM image of the precipitates in the grain interior, and the insets indicate the SADP and EDS analyses of Cu- and Nb-rich Laves phase particles, respectively; c typical co-precipitation of Cu- and Nb-rich particles observed by TEM; d TEM image of the precipitates at the grain boundary

Fig. 3 Dislocation characteristics in the specimen after creep deformation at 973 K and 50 MPa: a in the grain interior; b near the grain boundary

Fig. 4 Microstructures of the specimen after creep deformation at 1023 K and 50 MPa: a SEM image of the precipitates; b TEM image of the precipitates in the grain interior; c partially enlarged view in image b, and the insets show the SADP and EDS results for Cu- and Nb-rich phase particles, respectively

Fig. 5 Dislocation characteristics in the specimen after creep deformation at 1023 K and 50 MPa: a dislocation walls; b sub-grain boundaries; c interaction between precipitates and dislocations

Fig. 6 Microstructures of the specimen after creep deformation at 1123 K and 25 MPa: a SEM image of the precipitates; b TEM image of the precipitates in the grain interior; c TEM image of the precipitates at the grain boundary; d interactions between dislocations and precipitates

Fig. 7 Fracture surfaces of the specimens after creep rupture at conditions of a 973 K and 50 MPa; b 1023 K and 50 MPa; c 1123 K and 25 MPa

Fig. 8 Necking area beneath the fracture surface for the specimen fractured under conditions of a 973 K and 90 MPa; b 1023 K and 50 MPa

Fig. 9 a, b Typical creep curves of the experimental steel under different deformation conditions. c, d Creep rate curves corresponding to the images of a, b, respectively

Fig. 10 a Applied stress dependence of the minimum creep rate at all given temperatures. b Temperature dependence of the minimum creep rate at all given stresses

Fig. 11 Determination of the threshold stresses at different temperatures with the assumed true stress exponent of a 3; b 5

Fig. 12 a Effective stress (σ-σth) dependence of the minimum creep rate at all given temperatures. b Temperature dependence of the minimum creep rate at all effective stresses

Fig. 13 Monkman-Grant curves of the studied steel under different creep conditions

Fig. 14 Correlation between Larson-Miller parameter and applied stress under different creep conditions