A physically-based constitutive model for high temperature microstructural degradation under cyclic deformation

This paper presents a dislocation-mechanics cyclic viscoplasticity model which incorporates the key physical micro-mechanisms of strengthening and softening for high temperature deformation of 9Cr steels. In particular, these include precipitate and grain boundary strengthening, low-angle boundary dislocation annihilation and martensitic lath width evolution, using dislocation density as a key variable. The new model is applied to P91 steel across a range of strain-rates and strain-ranges in the 400-600 °C temperature range, for power plant header applications, to demonstrate the effect of key microstructural parameters on high temperature low cycle fatigue performance.