Deep insights on the creep behavior and mechanism of a novel G115 steel: Micromechanical modeling and experimental validation

Ultra-supercritical (USC) power plants with enhanced thermal efficiency have gained significant attention for reducing carbon dioxide (CO₂) emissions. A new tempered martensitic heat-resistant steel, so-called the G115 steel, shows great potential as the candidate for next-generation USC power plant components. However, so far, the intrinsic relationship between microstructure and creep response of this steel still remains ambiguous. In this study, we examined the microstructure-creep behavior relationship of the G115 steel by utilizing a combined experimental and micromechanical modeling approach. More specifically, the modified Orowan's equation was applied to evaluate the creep strain since dislocation motion was a basis of creep deformation. Three kinds of dislocation configurations were incorporated to model the evolution of the substructures, and meanwhile, the kinetic equations were also employed here to describe the damage evolution. The creep curves of G115 steel simulated by this model are reasonably good for up to thousands of hours compared with our experimental data. Moreover, the model outputs, i.e., dislocation densities and width of tempered laths, also agree well with the microstructural parameters achieved from the interrupted creep tests at 923 K and 140 MPa. Regarding the microstructural evolution during the creep process, internal dislocation density (mobile + dipole dislocation densities) first decreases rapidly along the steep slope, and then the rate of decline becomes slower with increasing creep time. In contrast, boundary dislocation density first increases whereas subsequently decreases due to the dominance of tempered lath growth in the later stage of creep. Our results suggest that the micromechanical creep model can fairly elucidate the relationship of microstructural parameters and creep response for G115 steel, which greatly enhances the fundamental understanding of its microstructural features for governing the creep responses.