Creep-Fatigue Interaction and Fracture Mechanism of X12CrMoWVNbN10-1-1 Steel

The creep-fatigue tests with load holding at maximum stress controlled by load with different stress ratios (0.2-0.4) and holding times (0.3-1.5 h) of X12CrMoWVNbN10-1-1 steel at 620℃ were carried out, and the creep-fatigue interaction and fracture mechanism of the steel were analyzed. The results show that the creep-fatigue life of the test steel had exponent relation with the holding time. The longer the loading time, the less the influence of stress ratio on creep-fatigue life. The creep fatigue interaction factor defined from the view of strain could well reflect the interaction between the true stress-true strain hysteretic curve and the creep fatigue life in the stable stage. The creep-fatigue fracture mode of the test steel was ductile fracture. When the holding time was short of 0.3, 0.5 h, the fatigue damage suppressed creep damage, and the damage was mainly controlled by cyclic fatigue load; the dimples on the fracture were caused by crystal boundary slide controlled by fatigue. When the holding time was long enough of 1.0, 1.5 h, the fatigue damage promoted creep damage, and the damage was mainly controlled by time-related creep load; the dimples on the fracture were caused by detachment of inclusions or second phase particles.