The material properties of a steel slab produced during continuous casting are significantly influenced by the kinetics of the austenite(gamma)-to-ferrite(alpha) phase transformation. Recent theoretical models either have used a semi-empirical approach (such as the Johnson-Mehl-Avrami equation) or simplified the coupled problem of the migrating interface and the diffusion of components by one of the following concepts: Local equilibrium is assumed at the interface implying an infinite interface mobility. Paraequilibrium is assumed at the interface. The coupled problem of interface migration and carbon diffusion is solved properly, however, substitutional components are assumed to be immobile and, thus, the system evolves to a final paraequilibrium state. Based on Onsager's principle of maximum dissipation rate the evolution equations for the diffusive fluxes and for the interface velocity are derived. This concept avoids any simplifying assumptions mentioned above. A computer program has been developed in order to apply this model for simulation of the gamma alpha diffusional phase transformation in Fe-alloys with low amounts of substitutional components such as Cr, Ni and Mn. The influence of the different solutes on the transformation kinetics has been studied. The routine is able to predict the transformation kinetics in Fe-alloys over the whole region ranging from diffusion controlled growth to interface mobility controlled growth (massive transformation).
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