COUPLED DIFFUSIONAL DISPLACIVE TRANSFORMATIONS - EFFECT OF CARBON CONCENTRATION

The nonequilibrium growth of partially supersaturated ferrite plates in Fe-C alloys is examined as a function of the carbon concentration, using a published theory for ''coupled diffusional/displacive transformations''. It is found that the theory correctly predicts the variation in the martensite-start temperature with carbon concentration, but fails to estimate the corresponding variations in the bainite-start temperatures of the same steels. This is attributed to the fact that the model does not include any variations in stored energy as a function of transformation temperature. The nature of the required variation in stored energy has been calculated by fitting against available data.