Multiaxial fatigue behaviour and damage mechanisms of P92 steel under various strain amplitudes and strain ratios at high temperature

High temperature multiaxial fatigue tests at different strain amplitudes and strain ratios were performed at 600 °C. Dynamic strain ageing (DSA) analysis and microstructure characterization were used to analyze the cyclic deformation and damage mechanisms. Results reveal that the increases in strain amplitude and strain ratio accelerate the cyclic softening. Moreover, the DSA behaviour shows a distinct dependence on the strain amplitude, strain ratio and loading direction. Furthermore, the increase in strain amplitude promotes subgrains growth and dislocation structure transformation. Particularly, the increase in strain ratio promotes the occurrence of planar slip of dislocation.