Interactions between solidification and fluid flow. Effects on cast structures and segregations

Abstract

Natural or forced fluid flow of the bulk melt can induce several changes in the solidification history of a casting : it may change the heat transfer conditions, the as-cast grain distribution, and the segregations. On the other hand, solidification can result in intense fluid flow due to natural solutal convection and in severe local segregations. The two following practical cases illustrate the variety and complexity of interactions between the fluid flow and the solidification of alloys : the effects of the stirring of the bulk liquid on the formation of the equiaxed zone during the continuous casting of steels, the formation of freckles and related segregations during the directional solidification of nickel-base alloys. Informations are given about, either new experimental observations, or updated physical and numerical models related to each case chosen here as examples. In the case of the influence of stirring on the formation of the equiaxed zone, emphasis is put on the importance of the interaction of the fluid flow with the dendrites in the coIumnar zone and in the stirred region itself. In the case of the freckles, evidence is brought forward that the dendritic nature and structure of the mushy zone are not the only causes of the dependence of the freckling on the heat transfer conditions during directional solidification.

Influence of forced convection on solidification and remelting in the developing mushy zone

“…The industry practice of continuous casting shows that the mushy zone and solid shell formed during solidification are mostly uneven, and this unevenness of shell growth might lead to surface defects or breakout in the worst case. Reasons for this are diverse: (1) the non-uniform heat flux from the casting to the mould [1][2]; (2) fragmentation of dendrites in the partially solidified shell [3][4]; (3) the dynamic flow-solidification interaction which leads to suppression of solidification or remelting locally [5][6][7]. The topic of non-uniform heat flux has drawn the significant attention of researchers [8][9][10].…”

Predictive Capabilities of Multiphysics and Multiscale Models in Modeling Solidification of Steel Ingots and DC Casting of Aluminum

“…There is therefore no nucleation barrier; equiaxed grains can grow freely on the fragments as soon as the temperature is below the local liquidus temperature. The complexity of this modeling lies in the quantification of a flux of fragments from the columnar zone [3,[17][18][19]. In DC casting of aluminum alloys, nucleation on TiB 2 or TiC inoculant particles is considered.…”

Thermo-fluid Mathematical Modeling of Steel Slab Caster: Progress in 21st Century

“…Shell thickness evolution as shown in Fig. 6 along the strand length is coupled with fluid flow in mold cavity 5,17) interaction with other phases present like inclusion and gas along with varying thermal properties of the solidified shell itself. Microscopically, solidification progress is dendritic in nature 61) but become a large problem to simulate the caster.…”

“…Interaction of fluid flow and solidification leads to washing effect, 4) hook formation, turbulence near mushy region and its growth. These interactions affect the as-cast structure mainly in equiaxed zone, 5) segregation, and natural solutal convection. These interactions take place in at various geometrical scales like dendritic scale where microsegregation is prevalent; here local solutal convection and steel-grade wise dendritic solidification growth characteristics governs the phenomena.…”