Creep behaviour and failure modelling of modified 9Cr1Mo steel

A finite element modelling (FEM) software is used to model the creep behaviour and damage mechanisms of modified 9Cr1Mo steel, CAsT3M 2008®, between 450 °C and 650 °C. Experimental creep results, collected from a large literature review, are used to identify parameters for a strain rate viscoplastic model that includes the effect of damage. Numerical calculations show good agreement with experimental data over the whole range of temperature considered. In particular, the drop off in time to rupture in the creep rupture curves is well predicted, and the change of failure mechanism from viscoplasticity-assisted ductile rupture to diffusion-assisted creep cavitation damage is highlighted. The identification of temperature-dependent hardening coefficients means the modelled strain results are also in a good agreement with experiments whatever the applied stress. The model is seen to have some limitations, but improvements are proposed to account for strain localizations and their geometrical effects.