Determination for the Entrapment Criterion of Non-metallic Inclusions by the Solidification Front During Steel Centrifug
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L continuous casting (CCC) is a method to produce round billet. During the casting, the mold, the support rolls, and the round billet rotate at a certain rotation speed. The molten steel passes through an inert gas protective atmosphere and flows down into the mold through a non-vertical nozzle. When the flow jet impacts the liquid steel meniscus, it creates gas bubbles that are carried by fluid flow and may be captured by the solidification front. The solidified shell grows and is continuously withdrawn from the bottom of the mold. As the molten steel is forced against the mold wall under a relatively high pressure due to the centrifugal force, it is reported that a uniform metallurgical structure of the billet can be achieved. So far, besides several patents declaring to produce steel pipes using CCC technology and some commercial advertisements, there have been very few reported studies on the transport phenomena during steel CCC process, including turbulent flow, heat transfer, multiphase flow, and solidification process. Because of high temperature and the opaque nature of the melt and the mold, it is hard to directly observe and QIANGQIANG WANG, Ph.D. student, and LIFENG ZHANG, Professor, are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing (USTB), Beijing 100083, China. Contact e-mail: [email protected] Manuscript submitted December 2, 2015. Article published online March 28, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
measure the fluid flow and other multiphase phenomena during steel continuous casting process. With the development of computer technology, numerical modeling of solidification during continuous casting process has widely applied as an effective tool for a better understanding the solidifying features. In the late 1960s and 1970s, Mizikar and Lait et al.[1] pioneered the first finite-difference model of shell thickness by solving a transient heat-conduction model. In 1990, the work of Voller and Brent proposed a fixed grid method and has been widely applied to solidification problem.[2,3] The essential feature of the fixed grid method is that during the solidification process, the latent heat evolves in the mushy zone, referring the region in the liquid–solid zone, and is accounted for in the governing energy equation by defining either a total enthalpy, an effective specific heat coefficient or a heat source term. Consequently, the numerical solution can be carried out on a space grid that remains fixed through the calculation. The fixed grid method can be categorized into models of equivalent heat capacity and enthalpy. The equivalent heat capacity model, which treats the latent heat effect into the specific capacity of the mushy zone, was proposed by Hsiao[4] and has been applied to analyze the fluid flow and solidification phenomena in funnel-type molds and to predict the areas be susceptible to cracking as a result of thermal stress.[5,6] The enthalpy model treats the enthalpy as a dependent variable in the energy conservation equation. In 1988, Brent et
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