Primary creep regeneration in 10%Cr martensitic steel: In-situ and ex-situ microstructure studies

Primary creep regeneration (PCR) is a phenomenon observed during stress-varying/cyclic creep loading conditions where a load reversal might clear the previous strain hardening memory and cause the regeneration of the primary creep regime (i.e. a period of high creep strain rate) upon reloading. In this study, in-situ and ex situ microstructural examinations, including transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), neutron and synchrotron X-ray diffraction were conducted to better understand the responsible mechanisms of PCR for a 10%Cr martensitic steel at 600 ?C. Our experimental evidence indicated that the PCR phenomenon is related to the change of dislocation density due to activation of dislocation generation and recovery mechanisms, formation and relaxation of dislocation pile-ups, as well as bowing/unbowing of dislocation lines during stress-varying creep loading conditions. These mechanisms could explain the observed creep strain accumulation in the steel during the examined stress-varying creep loading conditions reported in the current and previous studies. The presented mechanistic description of the PCR phenomenon and the reported experimental observations for the microstructural and mechanical parameters can provide a basis for the formulation of physically-based models to describe the creep behaviour of the steel under high-temperature stress-varying creep loading conditions.