Fatigue testing for an important turbine rotor material (X12CrMoWVNbN10-1-1 steel) was carried out over a wide range of strain and stress amplitudes at 873K. Particular attention was paid to the effect of control mode on the cyclic deformation behavior and life assessment at elevated temperature. Two main domains were observed depending both on the strain and stress amplitudes, where the effect of control mode was different. In the micro plastic deformation domain, the cyclic softening is slight and there is no clear difference in fatigue behavior between the stress and strain modes. In the plastic damage regime, stress cycling causes more significant softening or damage than strain cycling. The dependence of damage behavior on the evolution of dislocation substructure was focused. On the other hand, it is not possible to use strain based life model to predict fatigue life with the test results under a different control mode. A unified energy-based model is proposed based upon the deformation mechanism and the experimental results, which can assess the low cycle fatigue life with different control modes. The results obtained in this study could have significant implications in the design of structures.

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