Some aspects of mechanisms and modelling of creep behaviour of 2.25Cr-1Mo steel

The present work attempts to establish experimentally the dominant mechanism based model for describing the shape of creep curve at any arbitrary stress and temperature. Creep data were collected from literature and some were generated experimentally under different microstructural conditions of 2.25Cr-1Mo steel. Influence of thermal aging and pre-strain on the shape of creep curve have also been studied. The analysis of creep data clearly revealed that irrespective of initial microstructures, thermal aging significantly increases the tendency to soften whereas pre-strain results in marginal strengthening. Softening due to carbide coarsening was thus established as the dominant mechanism of creep in 2.25Cr-1Mo steel. A numerical procedure was developed to extract the parameters of the model, describing the kinetics of carbide coarsening directly from creep curves. A fairly accurate prediction of creep strain up to 5% was obtained using this approach. The kinetics of carbide coarsening was found to depend on the applied stress.