Abstract
Experiments are carried out to examine the ferrite formation in four lean construction steels of low carbon and low alloy contents during continuous cooling. The variation of the heat capacity during the transformation is measured by means of differential thermal analysis, and the heat capacity is converted to the volume fraction ferrite as a function of temperature. The ferrite growth is modelled in two ways: (i) according to an interface mobility model, and (ii) according to a diffusion control model. Different assumptions are made to model the geometry of the microstructure. It is shown that the interface mobility model, applying the proper driving force and geometry, can account for the experimental ferrite growth at the early stage of transformation, but carbon diffusion has to be taken into account quantitatively when the carbon concentration profile becomes significant. The simulation according to the diffusion control model is performed using the Dictra program based on the local equilibrium hypothesis. The resulting discrepancies with the experiments are partially due to the simple spherical geometry that is assumed.
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