Influence of Forced Flow on the Dendritic Growth of Fe-C Alloy: 3D vs 2D Simulation
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G the continuous casting of steel, the forced flow induced by external forces such as the pouring of the molten steel and electromagnetic stirring (EMS) influences the solidification microstructure and the quality of the steel strands greatly.[1] The forced flow changes the solute distribution in front of the columnar dendritic tip, thus causing the upstream growth of columnar dendrites. For example, with the introduction of mold electromagnetic stirring (M-EMS), the columnar dendrites become inclined clockwise or anticlockwise in the transverse section of high-carbon steel billets and blooms.[2,3] Moreover, the forced flow can promote the fragmentation of columnar dendrites and, accordingly, increase the number of equiaxed dendrites in front
WEILING WANG, ZHAOHUI WANG, SEN LUO, CHENG JI, MIAOYONG ZHU are with the School of Metallurgy, Northeastern University, Shenyang, 110819, P.R. China. Contact e-mail: [email protected] Manuscript submitted May 6, 2017.
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of the columnar dendrites, making the columnar-to-equiaxed transition (CET) much easier.[4] Practically, M-EMS is employed to improve the ratio of equiaxed dendrites and reduce the central segregation of high-carbon steel strands. Therefore, the investigation of the forced flow caused by the interaction of pouring and M-EMS and its effects on the solidification behavior of steel strands at the macroscopic scale has drawn much interest from metallurgists.[5–7] However, based on obtained results, such as the superheat dissipation and the shell thickness, a direct quantitative relationship between the processing parameters and the solidification quality cannot be made because the dendritic structure, as the intermediate link, is omitted. As a result, metallurgists have increasingly focused on the effect of the external forces on the evolution of the dendritic structure.[2,8,9] An understanding of the dendritic growth of alloys with the forced flow is necessary to predict the quantitative relationship between the processing parameters and the dendritic structure of the steel strands further. Because steel is optically opaque, the dendritic structure after complete solidification is used to determine the dependence on the forced flow.[8,9] On the one hand, the
dendritic structure is inevitably affected by the cooling process from complete solidification to room temperature. On the other hand, some important phenomena such as dendrite fragmentation during dendrite evolution with forced flow cannot be observed. Fortunately, with the synchrotron X-radiation imaging technique, the in situ observation of the dendritic evolution of steel is possible.[10] The influence of forced flow on the dendritic evolution was first observed in a Ga-In alloy with a low melt temperature.[11] In addition to experimental studies, numerical approaches aimed at formularizing the functional relationship between the characteristic parameters of the dendritic tip and the flow intensity or visualizing the dendritic morphology with the flow also play an important role
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