Study on low-cycle fatigue behavior and life prediction of Cr–Ni–Mo–V gun steel at room temperature and 600 ℃

An investigation was conducted on the fatigue under low cyclic loading of the Cr–Ni–Mo–V gun steel at both room temperature (RT) and 600 ℃. Fracture progression and deformation mechanisms were assessed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Considerable monotonic and cyclic softening were observed at RT and 600 ℃. The specimen exhibited a stable fatigue behavior until 80% and 70% of its fatigue life. This behavior coule be attributed to its microstructural characteristics obtained during the fatigue tests. Dislocation movement, contact, and annihilation contributed to the formation of dislocation networks (DNs), dislocation walls (DWs), dynamic recovery, and recrystallization. The SEM results indicated that fatigue cracks typically began near the surface. As the temperature increased, the failure mode gradually shifted from mixed transgranular and intergranular fractures to intergranular fractures possibly owing to the reduced grain boundary strength and easy oxidation of the grain boundary at high temperatures. In addition, a model was created to predict fatigue life by utilizing a quadratic function of the energy dissipation derived from the hysteresis curve. This model took into account the influence of temperature on the parameters, offering a practical method for enhancing the fatigue performance of the Cr–Ni–Mo–V gun steel under various temperature conditions.