Numerical Investigation of Shell Formation in Thin Slab Casting of Funnel-Type Mold
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THIN slab casting (TSC) is increasingly implemented, in competition with conventional slab casting, for producing flat/strip products due to its advantages of integrating the casting-rolling production chain, energy saving, high productivity, and near net shape.[1,2] However, problems such as the sensitivity to breakout and edge/surface cracks were frequently reported. These problems have encouraged metallurgists to consider a special mold design,[3–5] cooling system, and submerge entry nozzle (SEN)[6–8] to use a special mold flux[9] and even to apply electromagnetic braking in the mold region.[7,8,10] The modeling approach becomes a useful tool to assist the system design.[5–8,10–18] One striking feature of TSC, different from that of conventional slab casting, is the use of the funnel-type mold, which provides the necessary space for the SEN to conduct liquid melt into the thin slab mold. Another important feature is the shell thickness which solidifies in the mold A. VAKHRUSHEV, Senior Researcher, is with the ChristianDoppler Lab for Adv. Process Simulation of Solidification & Melting, Department of Metallurgy, University of Leoben, Franz-Josef-Str. 18, 8700 Leoben, Austria. M. WU, Associate Professor, is with the Christian-Doppler Lab for Adv. Process Simulation of Solidification & Melting, Department of Metallurgy, University of Leoben, and also Department of Metallurgy, University of Leoben. Contact e-mail: [email protected] A. LUDWIG, University Professor, is with the Department of Metallurgy, University of Leoben. Y. TANG and G. HACKL, Project Managers, are with the RHI AG, Technology Center, Magnesitstrasse 2, 8700 Leoben, Austria. G. NITZL, Product Manager, is with the RHI AG, Wienerbergstrasse 9, 1100 Vienna, Austria. Manuscript submitted July 3, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
region: 40 to 50 pct of the slab thickness for TSC.[3] In comparison, there is only 20 to 30 pct of slab thickness which solidifies in the mold region for the conventional slab.[19,20] Therefore, the evolution of solid shell under the influence of turbulent flow and subject to the continuous shell deformation in TSC becomes a critical issue for the modeling approach. Different models were used to calculate solidification of TSC. One of these is the so-called ‘equivalent heat capacity model’, as proposed by Hsiao.[21] This model was originally proposed for the solidification without solid motion, as the transport of latent heat in the mushy zone due to the motion of the solid phase is not considered. According to recent investigations,[22,23] the transport of latent heat in the moving (deforming) mushy zone plays a very important part in continuously cast and solidified objects, e.g., continuous casting. The treatment of the motion of the solid phase has a significant influence on the advection of the latent heat, and hence on the evolution of the mushy zone. In order to consider the advection of latent heat under the condition of deforming and moving mushy zone, an enthalpy-based mixture solidification model is favored.[
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