Low cycle fatigue and creep-fatigue interaction behavior of 2.25CrMoV steel at high temperature

This paper presents a comprehensive investigation into the low cycle fatigue (LCF) and creep-fatigue interaction (CFI) behavior of 2.25CrMoV steel at an elevated temperature of 455 °C. The LCF tests are conducted using a triangular waveform with varying strain amplitudes ranging from 0.4 % to 0.7 %. Furthermore, the CFI tests are conducted using a trapezoidal waveform with different hold times and hold directions. To gain further insights, the microstructure and fracture behavior of the steel are characterized using optical, scanning, and transmission electron microscopy techniques. The results reveal that the softening behavior and fatigue life degradation of the steel are dependent on the applied strain amplitude, hold time, and hold direction. Higher strain amplitudes in the LCF tests lead to an increased number of crack initiation sources. During the CFI tests, fatigue fracture is identified as the primary failure mechanism under tensile hold conditions, and an increase in hold time promotes crack propagation. The interaction between fatigue and creep is found to be more significant in compressive hold and tensile compressive combination hold conditions. Microstructure analysis demonstrates that the lath structure recovers during cyclic loading, resulting in cyclic softening. Finally, a modified energy-based model is proposed to distinguish the different roles of tensile energy and compressive energy in the fatigue process. The proposed model accurately predicts the fatigue life of the 2.25CrMoV steel, as demonstrated by the good agreement between the experimental and predicted results.