In-phase thermomechanical fatigue studies on P92 steel with different hold time

Abstract The effect of hold time with 0, 20, and 40 s on in-phase thermomechanical fatigue (TMF) behavior and life of P92 steel is investigated in this study. TMF tests are carried out under mechanical strain control with strain amplitudes of 0.4 0.4 , 0.6 0.6 , and 0.8 % 0.8\text{\%} , and temperature range of 550–650°C which is closely relevant to the operating condition in power plant. TMF tests are performed in a mechanical strain ratio of R = − 1 R=-1 and cycle time of 120 s. The fatigue life variation follows the sequence of N f 0 s < N f 20 s < N f 40 s {N}_{\text{f}}^{0\hspace{.1em}\text{s}}\lt {N}_{\text{f}}^{20\hspace{.1em}\text{s}}\lt {N}_{\text{f}}^{40\hspace{.1em}\text{s}} for the same mechanical strain amplitude. In addition, the influence of hold time on fatigue life decreases with the increasing strain amplitude. A continuous softening can be observed from the cyclic stress response under all test conditions. Fractographic and microstructural tests indicate that the fracture surfaces are characterized by a multi-source cracking initiation and an oxidation phenomenon. Furthermore, a modified Ostergren model is used to predict the fatigue life and achieves a good predicted result.