Study of the Mechanism of Liquid Slag Infiltration for Lubrication in Slab Continuous Casting
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ODUCTION
MOLD powder was first applied to the continuous casting (CC) of steel in 1963.[1] The powder added on the meniscus of molten steel is expected to perform the following tasks: protect the liquid steel from oxidation, absorb floating inclusions, provide thermal insulation, lubricate the strand and control heat transfer between the mold and the solidifying shell[2]; among these, the lubrication of the solidifying shell plays an important role, as the initial solidifying steel shell is too weak and sticky to be smoothly withdrawn from the mold.[3] The origin of the majority of surface defects is at or within 25 mm of the meniscus in the mold.[4,5] Thus, consistent and uniform lubrication, especially in the meniscus region during the CC process, is crucial for the smooth demolding and uniform growth of the solidifying shell and is also an essential premise for the production of defect-free casting. The lubrication is realized by the infiltration of liquid slag into the mold-strand channel, and many studies[6–16] have been conducted to gain an understanding of the mechanism responsible for slag infiltration, as summarized in Table I.
SHAODA ZHANG, QIANGQIANG WANG, SHENGPING HE, and QIAN WANG are with the College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China. Contact e-mail: [email protected] Manuscript submitted December, 4 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
For cold models using oil silicone,[11] the condition tends to be isothermal whereas the conditions in the mold are not isothermal. The freezing of water as a medium simulating the slag has also been reported.[17] However, water may be a reasonable substitute for the viscosity of steel but not for the surface and interfacial tension terms.[1] Though adequate operational conditions could be found in high-temperature laboratory experiments[7,18] in which the experimental apparatus contains molten steel and mold flux[6] or low-melting Sn-5 mass pct Pb alloy and stearic acid,[7] the inflow behavior of liquid flux into the channel could not be determined. For the description of the slag infiltration process by the approach of the mathematical model, different conclusions have been obtained even with respect to the occurrence time of slag infiltration into the mold-strand channel.[9,10,12,16] Someone determined that the liquid slag infiltrated into the channel during the tn period because of the increased pressure produced by a descending slag rim. While the channel became blocked because of the bending of the initial shell, others found that the flux inflow was difficult in the tn period and could take place only during the tp period. The above controversy may derive from the differences of the studied objects and slag properties used and the adoption of calculation assumptions (such as the neglect of top surface fluctuation, the predefined solid slag layer against the mold wall, without or with a constant shape of solid slag rim around meniscus). However, without a clear clarification of the mechanism of slag infiltration during t
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