Evolution of Temperature and Solid Slag Film During Solidification of Mold Fluxes
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D flux plays an important role in continuous casting.[1] The liquid slag on the top of the mold infiltrates into the gap between the strand and the mold, then a thin liquid slag film on the shell side could lubricate the strand. Meanwhile, the solid slag film on the mold side could control the horizontal heat transfer for the steel grade being cast.[1,2] In routine practice, the rate of heat removal from the shell is important for the slab surface quality. On the one hand, the thermal resistance between the mold and shell can be increased by increasing the thickness of the solid slag film.[3,4] On the other hand, the formation of a thicker solid slag film may reduce the consumption of mold flux during continuous casting. Solid slag film with a high crystalline fraction can control the heat transfer from the shell to the mold. However, the precipitation of crystals with large size may deteriorate the lubrication effect of mold fluxes.[5] Therefore, the structure of the solid slag film is an important factor that could affect the performance of mold flux during continuous casting. Generally, the structure of solid slag film can be discussed according to the crystallization behavior of mold fluxes.[6] However, the temperature profile used in tests may be different from the thermal history of the slag film in the mold. It is reported that the cooling rate between the steel shell and the mold changes with distance and time,[7] whereas the temperature is always decreased linearly during experiments such as
CHANGLIN YANG, GUANGHUA WEN, QIHAO SUN, and PING TANG are with the State Key Laboratory of Mechanical Transmission, College of Materials Science and Engineering, Chongqing University, Chongqing, 400044 P.R. China Contact e-mails: [email protected], [email protected] Manuscript submitted October 11, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
Differential Scanning Calorimetry (DSC) measurement and hot thermocouple technique measurement.[8,9] Therefore, it is difficult for these techniques to analyze the structure evolution of slag film during solidification, although the behavior of crystals under a given temperature profile can be well understood. Considering the necessity of studying the structure of the solid slag film, mathematical model and experimental methods were used to describe the performance of mold flux in continuous casting. Meng and Thomas developed a mathematical model to simulate the microstructure and the behavior of interfacial mold slag layers.[10,11] This model is capable of interpreting the crystallization behavior of slag layers between the shell and the mold. In order to observe the formation process of the slag film, the double hot thermocouple technology (DHTT) is used to simulate the temperature gradient between the shell and the mold.[12–15] However, because the methods used to prepare samples are different for different tests, the DHTT test is difficult to be coupled with the experimental methods used to study the structure of the solid slag film, such as X-ray diffraction (XRD) and scanning electron microscope (SEM). Th
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