Study on the Macrosegregation Behavior for the Bloom Continuous Casting: Model Development and Validation
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CONTINUOUS casting (CC) of steel is a typical solidification process for various commercial multicomponent alloys. As solidification proceeds, macrosegregation will be produced in the strand due to the macroscopic transportation of the solute-rich liquid at the solidification front by the fluid flow within the mushy and liquid regions, which has been the bottleneck for the internal quality upgrading of the casting products, especially for heavy sectioned or high-carbon steel bloom. Such segregation cannot be eliminated by the subsequent hot working process, which will lead to poor or nonuniform mechanical properties of steel products. Therefore, a thorough understanding of the transport phenomena in the CC system is needed to improve the process control to the internal quality of the casting strands. For the efficiency limitation of industrial tests to the complex metallurgical behavior in the CC process, previous researchers have devoted significant efforts to develop the mathematical models for better understanding of the macrosegregation formation during solidification. As early as 1967, Flemings and colleagues[1,2] proposed a model for the description of macrosegregation based on the mass equilibrium principle of solute in HAIBO SUN, Ph.D. Candidate, and JIAQUAN ZHANG, Professor, are with the Department of Metallurgical Engineering and State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, 100083 Beijing, P.R. China. Contact e-mail: [email protected] Manuscript submitted July 1, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
the case of an ignorable effect of mushy zone dendritic structure on the melt flow. To precisely describe the flow status in the mushy zone, Mehrabian et al.[3] refined the Flemings’ model through treating the mushy region as a porous medias, where the interdendritic fluid flow was calculated by Darcy’s law. For the permeability in Darcy’s law, Felicelli et al.[4] and Poirier[5] pointed out that the permeability is anisotropic with the components of Kpar and Kver to represent the resistance of the flow parallel and vertical to the primary dendrite arms in the columnar-dendritic structures region, and it is isotropic in the equiaxial dendritic structures region, respectively. Moreover, to simultaneously achieve the detailed coupling between microscopic and macroscopic phenomena in the process of alloy solidification, Neilson and Incropera,[6] Bennon and Incropera,[7]and Diao and Tsai[8] employed the classic mixture theory[9] to establish the continuum models, while Beckermann and Viskanta,[10] Ni and Beckermann,[11] and Poirier et al.[12] developed the volumetric averaging models by adopting the volumeaveraging technique.[13] Based on the models above, a lot of studies on the characteristic and formation mechanism of the macrosegregation in the processes of ingot casting and directional solidification have been carried out.[14–16] Combeau et al.[17] developed a multiphase and multiscale mathematical model to investigate the influence of motion and morphology of the equiax
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