Cyclic deformation and damage mechanisms of 9%Cr steel under hybrid stress-strain controlled creep fatigue interaction loadings

The hybrid stress–strain controlled creep-fatigue interaction (HCFI) loadings at various dwell conditions were conducted on 9%Cr steel at 625 °C to investigate the deformation and damage mechanisms. Results reveal that the HCFI tests with conservative dwell conditions show complicated cyclic responses and low creep strain. The failure specimens demonstrate strong creep-fatigue interaction damage (CFID) with many branched surface cracks. With the increase in dwell stress and time, the HCFI tests show continuous softening and remarkable creep deformation. The creep-dominant damage (CDD) featured by internal creep cavities and blunt surface cracks leads to the final failure.