Creep damage initiation in high-temperature steel: a comparative study of ferritic, martensitic and austenitic microstructures

Abstract Premature failure of critical energy infrastructure caused by creep damage, threatens productivity and safety, emphasizing the need for robust methods to monitor and predict material performance. Creep damage nucleation in metals is driven by nano- and micro-structural features, but linking these early evolutions to later failure is complex. This study presents a correlative methodology integrating SEM, FIB, EBSD, EDX, TEM, image recognition, data analysis and crystal plasticity simulations to investigate creep cavity formation in ferritic Grade 91, martensitic Grade 91 and austenitic 316H steels. Results show that grain boundaries and localized deformation strongly influence creep cavity initiation. MnS inclusions drive cavity nucleation in Grade 91 steel, while grain boundary ferrite and M 23 C 6 carbides dominate in 316H steel. Calibrating a crystal-plasticity framework with experimentally identified precursors reveals that deformation, inclusions and precipitates translate into damage-sensitive indicators such as slip rate hotspots and volumetric strain, enabling prediction of early creep cavity nucleation mechanisms.