Oscillation-Mark Formation and Liquid-Slag Consumption in Continuous Casting Mold
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ag powder fed onto the top of molten steel in a continuous casting mold prevents the metal from oxidizing and melts to form a liquid-slag pool covering the free surface of casting steel, as illustrated in Figure 1. The liquid slag infiltrates into the gap between the mold wall and the steel surface to be consumed incessantly and to play the important role of lubricant because the initial solidifying steel shell is too weak and sticking to be smoothly withdrawn from the mold.[1,2] In particular, the surface cracks of the steel slab and the breakout have a high potential to be induced by the friction force as a result of the mold oscillation. The liquid slag close to the water-cooled mold cools as a resolidified layer and that close to the high-temperature metal remains as a liquid-slag layer. The liquid- and solid-slag layers decide the gap contact between the mold wall and the casting metal, which is crucial to steel slab quality, by influencing the interdependent thermomechanical behaviors inside these layers. The solid-slag JIE YANG, XIANGNING MENG, NING WANG, and MIAOYONG ZHU are with School of Metallurgy, Northeastern University, Shenyang 110819, P.R. China. Contact e-mail: [email protected] Manuscript submitted March 23, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
layer presents the characteristics of crystalline and glassy and mainly shares responsibility for the task of controlling the heat transfer from the high-temperature steel shell to the mold wall via its thermal conductivity and the thermal contact resistance between the resolidified slag and the hot wall surface.[3–5] Nevertheless, the liquid layer not only contributes to the thermal process in mold, but it also provides a place for a complex multiphysics phenomenon coupled with mold oscillation, involving liquid-slag infiltration and lubrication, initial solidifying shell deformation, as well as dynamic pressure change. Generally, this place is defined as the flux channel from the free surface of casting steel to a position with zero dynamic pressure, i.e., no pressure caused by mold oscillation, and connected to the atmosphere. Many studies have been conducted to shed light on the multiphysics phenomena in the flux channel through a variety of approaches. Meng and Thomas[6–8] described a comprehensive model that includes a transient calculation of heat conduction within the solidifying steel shell coupled with a steady-state heat conduction within the mold wall. The model was applied to study the effect of casting speed and mold powder viscosity properties on the slag layer behavior between the oscillating mold wall and the solidifying steel shell. They indicated that the liquid slag lubrication produces
Fig. 1—Transient phenomena in continuous casting mold.
negligible stresses and the lower slag consumption rate leads to high solid friction and results in a solid-slag layer fracture. Furthermore, the crystallization behavior of slag layers in the interfacial gap between the mold and the steel shell was interpreted and a mechanism for the formati
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