A 3D meso-scale solidification model for metallic alloy using a volume average approach

A 3D discrete-element model has been developed to simulate the solidification of steel at the meso-scale. The domain consists of a set of equiaxed grains along with the liquid channels, where the fully solid grain shape is given by a modified Voronoi diagram. The primary solidification and peritectic transformation within each grain is modeled using a volume average approach. Thus, phase evolution within the semisolid domain with either dendritic or globular microstructure can be predicted depending on different cooling rates. The coalescence phenomenon between grains is considered at the end of solidification using Bulatov's approach for estimating interfacial energy. It is seen that only 0.9% of the grains are attractive based on their orientations, significantly depressing final-stage solidification. The results demonstrate the ability of this modelling approach to investigate morphology transitions during the solidification of alloys having a range of composition from non-peritectic to hyper-peritectic. The influences of grain size, carbon content and cooling rate on the solidification behavior are also investigated. Further, it is shown that the semi-solid morphology of hypo-peritectic steel alloys at high solid fraction contains very thin liquid channels, in comparison to other compositions, when the peritectic transformation occurs thus increasing the hot tearing susceptibility. This meso-scale model will be used in conjunction with semi-solid fluid flow and deformation simulations for multi-physics modelling of solidification.