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 0.40.4, 0.60.6, 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=−1R=-1 and cycle time of 120 s. The fatigue life variation follows the sequence of Nf0s<Nf20s<Nf40s{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.

Keywords

• p92 steel
• in-phase thermomechanical fatigue
• hold time
• fatigue life
• modified ostergren model