Experimental and Numerical Studies on the Influence of Hot Top Conditions on the Macrosegregation in an Industrial Steel Ingot
Résumé
Although a significant amount of work has been already devoted to the prediction of the macrosegration in steel ingots, the majority of studies considered the solid phase as fixed. It has been shown that with such an assumption it is not possible to predict the macrosegregation in the centre of heavy steel ingots. The motion of the equiaxed grains is generally suspected to be the cause of this macrosegregation. We developed a multiphase and multi-scale model, which is able to describe the evolution of the equiaxed crystals and to take into account their motion. Fragments of dendrites are assumed to be at the origin of the equiaxed grains. The flow of the interdendritic liquid when the grains pile up and are packed is also described. The model was numerically implemented using a 2D finite-volume formulation. We applied the model to study the development of the macrosegregation and the macrostructure in a 65 ton steel ingot that was experimentally analyzed. The ingot was cast with particular conditions. A metallographic study was performed and the macrosegregation pattern was characterized. The macrosegregation pattern predicted by the model is presented and compared to experimental results. It is shown that in the case of such a heavy ingot, the motion of the equiaxed grains is indeed the main cause of the negative macrosegregation in the centre of the product