Microstructures of creep-fatigued 9–12% Cr ferritic heat-resisting steels

FE-SEM and TEM observations revealed a multiscale structure consisting of prior austenite grains, packets, blocks and subgrains for 9–12 mass% Cr ferritic heat-resisting steels. During a creep-fatigue test the microstructure showed significant changes in subgrains within the block and the particle size and the precipitation density on the prior austenite grain boundaries. The block size showed little changes. The creep-fatigue life depends on the occupancy of the precipitates on the prior austenite grain boundaries as well as the local recovery processes near prior γ grain boundaries.