In many engineering castings, forced flow is implemented to promote the equiaxed zone, and the primary
source of the equiaxed is considered to be dendrite fragmentation. It is known that the interdendritic flow
in the dendrite growth direction promotes dendrite remelting, creating favorable conditions for dendrite
fragmentation. Therefore, a flow-driven fragmentation model was primarily proposed, assuming that
fragmentation occurs when the following criterion, (u_l-u_c)⋅∇c_l<0, is fulfilled. Although the above model
has considered global transport phenomena and their impacts on the local thermodynamic condition for the
dendrite remelting, some other microscopic events influencing the fragmentation were ignored or
simplified. One such event is the timing effect of dendrite pinch-off. In this conference contribution, a
literature survey on the study of the dendrite pinch-off is made, and on this base, a modification to the
previous flow-driven fragmentation model is suggested. In addition to the above flow-driven remelting
criterion, a second condition, i.e., the necessary time for the remelting (t_r) of the dendrite roots to allow
the pinch-off (τ) to occur, is applied to the model. As an evaluation effort, this newly improved model was
used to simulate two engineering castings: one is the directionally solidified superalloy casting, and one is
an in-laboratory cast steel ingot. It is verified that a better simulation-experiment agreement is obtained
with the new model modification