We document the evolution of dislocation densities in the tempered martensite ferritic steels during long-term aging and creep. Scanning transmission electron microscopy in combination with a high-angle annular dark-field detector is used to study dislocations in a 12% Cr steel.
During aging, the dislocation density quickly decreases by a factor 2 and then remains constant. Long-term creep results in an initial decrease by a factor 10, after this sharp drop, the dislocation density continue to decrease.