The influence of temperature transients on the lifetime of modern high-chromium rotor steel under service-type loading

Nowadays, fossil power plants are increasingly required to start up and shut down frequently due to the flexibility of electrical power demand. Thermomechanical fatigue (TMF) induced by temperature transients with superimposed creep on the heated surfaces of components leads to a significant reduction of lifetime. In this paper, the influence of temperature transients on the crack initiation behavior of high-chromium rotor steel of the type X12CrMoWVNbN10-1-1 was studied by performing uniaxial and biaxial service-type TMF experiments. The experiments represent a range of steam turbine cycles with a maximum temperature of 600° C. A significant lifetime reduction was observed on TMF loading compared to isothermal loading under the same mechanical strain cycle. Metallographic examinations have been employed to characterize the associated thermal fatigue damage mechanisms for comparison of the damage evolution under isothermal loading. In particular, the evolution of damage was investigated by systematic metallographic examinations to study the temperature influence on the crack initiation behavior.