Modeling of equiaxed growth in multicomponent alloys accounting for convection and for the globular/dendritic morphological transition

A lagrangian model has been developed to predict the evolution of a single equiaxed crystal moving into an infinite medium, and intended to be coupled with a macroscopic code devoted to the solidification of large cast products. A particular attention is paid to the transition from globular to dendritic crystals because both morphologies can be observed in cast products. First, the model has been compared with experiments of settling NH4Cl crystals in NH4Cl-H2O melts. Good agreements have been achieved provided that a suitable value is chosen for the stability constant of the dendrite tip growth model. The model is then applied to a multicomponent steel so as to outline the link between the morphology and the sign of the chemical segregation. Finally, the trends drawn from the model concerning the change in morphology are discussed so as to explain the concomitancy of the structural and chemical patterns observed in the equiaxed zone of heavy steel ingots.