Research on High‐Temperature and High‐Cycle Fatigue Fracture Mechanism of Fe–25Mn–9Al–8Ni–1C–0.2Ti Alloy

In order to solve the problem that the cylinder head material of high power density diesel engine is prone to fatigue failure at high temperature, in this study, low density iron‐based alloy (Fe–25Mn–9Al–8Ni–1C–0.2Ti) is prepared by vacuum induction levitation melting method, and its high cycle rotating bending fatigue properties at room temperature and high temperature (600 °C) are studied. The results show that the fatigue strength at 600 °C (255 MPa) is 37.3% higher than that at room temperature (183 MPa). At 600 °C, the hardness of ferrite and austenite increases by 36.33% and 42.23%, respectively, compared with that at room temperature. The reasons are as follows: Firstly, at 600 °C, κ‐carbides are formed in the microstructure, the existence of TiC in the microstructure and the increase of ferrite volume fraction also play a role. In addition, at 600 °C, dense and stable oxide films (Fe 2 O 3 , Al 2 O 3 , and Mn 2 O 3 ) are continuously formed in the fatigue source region, which inhibits the crack initiation to some extent. Furthermore, the thermal conductivity at 600 °C is about twice as high as that at room temperature, and the higher thermal conductivity reduces the internal thermal stress of the alloy, thus improving the fatigue performance of the alloy.