Revealing the influences of strain amplitudes on hybrid stress–strain controlled creep-fatigue interaction responses for 9 %Cr steel

•The hybrid-controlled creep-fatigue interaction (HCFI) tests at different strain amplitude were performed.•The influences of strain amplitude on HCFI tests, including macroscopic response and microscopic damage, were systematically investigated.•A dwell indicator (DI) based on HCFI macroscopic behaviors and the low cycle fatigue data was proposed. The hybrid stress–strain controlled creep-fatigue interaction (HCFI) tests were performed on 9 %Cr steel at strain amplitudes ranging from ± 0.25% to ± 0.6%. The strain amplitude increase brings more possibilities of cracking but fewer crack deflections, along with some differences in LABs and grain size. But for HCFI tests with high creep damage, strain amplitude plays a minor role since considerable creep strain during stress holding is converted into fatigue strain even at low strain amplitudes. Additionally, a dwell indicator (DI) benchmarked against macroscopic LCF responses is proposed to evaluate strain amplitude-induced microscopic HCFI damage. When DI is approximately equal to (or greater than) 0.9, the differences in strain amplitudes can bring significant changes in internal degradation and fracture behaviors. When DI is close to (or lower than) 0.5, HCFI damage exhibits low sensitivity to strain amplitude.