High energy synchrotron X-ray diffraction characterization of EUROFER97 steel under high temperature tensile and ratcheting testing

The thermo-mechanical response of reduced activation ferritic martensitic steel EUROFER97 is governed by dislocation-mediated deformation processes, which are critical for designing and predicting structural behavior under fusion-relevant loading conditions. In this study, the deformation behavior of batch-2 EUROFER97 is investigated using in-situ high energy synchrotron X-ray diffraction during monotonic tensile testing from room temperature to elevated temperature (nominal 500°C, corresponding to a measured value of 460°C) and asymmetric cyclic tensile loading at 460°C. Monotonic tensile tests are used to establish baseline temperature-dependent evolution of dislocation character and density. The primary focus is on asymmetric cyclic tensile loading, representative of ratcheting conditions, during which cycle-resolved analysis of dislocation recovery is realized. Diffraction line profile analysis is employed to quantify total dislocation density and the relative contributions of edge and screw components. The experimental data are interpreted using physically based recovery models, allowing extraction of activation energies and volumes associated with character-specific dislocation recovery. The results show that, while the overall deformation behavior is consistent with previously reported trends in EUROFER97 and related steels, the present work provides quantitative characterization of recovery parameters under non-fully reversed cyclic loading. These parameters offer physically meaningful input for dislocation-based constitutive models describing cyclic plasticity and ratcheting. The findings support the transferability of micromechanical deformation behavior across industrial batches, while emphasizing the importance of dislocation kinetics in designing and modelling fusion structural materials under thermo-mechanical loading.