Columnar and equiaxed dendrite growth in continuously cast products

A model able to predict solidification structures in continuously cast products has been proposed. This model provides a description of the solidification kinetics coupled with heat transfer. It deals with both macroscopic and microscopic aspects of solidification. In a first approach, the fluid flow description was simplified and roughly evaluated. The columnar‐equiaxed transition predicted by the model was found to agree with the observations made on square blooms cast in high‐C steel with moderate electromagnetic stirring. The modelling showed that heterogeneous nucleation alone cannot account for the known effect of electromagnetic stirring on the solidification structure which can only be explained by the multiplication of cristallites by erosion of the solidification front. The free cristallite formation is the only part of the model where the lack of fundamental data made necessary to adjust the theoretical parameters to the experimental results. The description of the constrained and unconstrained dendrite growth was made according to the relationships proposed by Kurz and Fisher and Lipton, Glicksman and Kurz, respectively. The description of the dendrite tip as a paraboloid of revolution rather than a half sphere, has a major effect on the system behaviour description. This investigation has underlined an important experimental fact: the average primary grain diameter in the bloom centre remains constant with reduced superheat or increased cooling or enforced stirring.