Abstract: Creep fatigue interaction(CFI) is the primary factor which restricts the safe operation of high-temperature components in many fields. Two modes, conventional strain-controlled creep fatigue interaction(CCFI) and hybrid stress-strain controlled creep fatigue interaction(HCFI) are adopted to study the creep-fatigue properties of G115 martensitic heat resistant steel. In addition, the accumulation of creep damage and microstructural evolutions under these two modes are compared. The effects of total strain range, load holding time, and load holding stress on creep-fatigue properties of G115 steel are emphatically analyzed. The results show that the rupture lives of CCFI and HCFI are reduced as the total strain range increased. Moreover, the rupture life of HCFI is reduced with the increasing hold stress and hold time. The accumulated creep strain in one cycle increased when the hold stress or the hold time increased in HCFI. This indicated that HCFI test is more suitable for characterizing creep-dominated CFI. For creep-fatigue life prediction under two modes, the predictive accuracy of time-fraction(TF) method, ductility-exhaustion(DE) method and modified strain energy density exhaustion(MSEDE) method are discussed. The results show that the MSEDE method can better describe creep damage in creep-fatigue considering the effect of average stress on creep fatigue. For HCFI, the average creep rate is used to modify DE and MSEDE models, which reduces the mean relative error of prediction by half.

Key words: creep-fatigue, hybrid stress-strain controlled, life prediction, damage evolution