A precipitate evolution-based continuum damage mechanics model of creep behaviour in welded 9Cr steel at high temperature

A multiaxial, physically based, continuum damage mechanics methodology for creep of welded 9Cr steels is presented, incorporating a multiple precipitate-type state variable, which simulates the effects of strain- and temperature-induced coarsening kinematics. Precipitate volume fraction and initial diameter for carbide and carbo-nitride precipitate types are key microstructural variables controlling time to failure in the model. The heat-affected zone material is simulated explicitly utilising measured microstructural data, allowing detailed investigation of failure mechanisms. Failure is shown to be controlled by a combination of microstructural degradation and Kachanov-type damage for the formation and growth of creep cavities. Comparisons with experimental data demonstrate the accuracy of this model for P91 material.This publication has emanated from research conducted with the financial support of (i) the Irish Research Council under Project Number GOIPG/2015/3944 and (ii) Science Foundation Ireland as part of the MECHANNICS joint project between NUI Galway and University of Limerick under Grant Number SFI/14/IA/2604