Characteristics of Slag Infiltration in High-Mn Steel Castings
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gh-Mn steel has exhibited noticeable product performance, such as a high tensile strength and extraordinary ductility, which has led to considerable attention in the automotive and offshore industries. However, the addition of Mn into steel leads to poor casting performance due to the strong chemical reactions at the interface between the molten steel and mold flux.[1,2] During casting, the interfacial reaction is mainly governed by the Mn content in the molten steel, where SiO2 in the mold flux is significantly reduced by Mn and consequently increases MnO in the mold flux. This changes the physicochemical properties of the slag, inducing unstable heat transfer and lubrication in the interfacial gap between the mold and the solidifying shell.[3] Previous studies have attempted to develop a new generation of mold fluxes for the casting of high
JIE YANG and DENGFU CHEN are with the College of Materials Science and Engineering, Chongqing University, Chongqing, 400044, P.R. China. Contact e-mails: [email protected]; chendfu@ cqu.edu.cn ZHAOZHEN CAI and MIAOYONG ZHU are with the School of Metallurgy, Northeastern University, Shenyang, 110819, P.R. China. Manuscript submitted September 28, 2018.
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Mn-high Al steels, including a conventional CaO-SiO2type mold flux with low basicity and a nonreactive CaO-Al2O3-type mold flux. A series of fluxing agents, such as B2O3, Li2O, and BaO, were added to optimize the mold flux properties for the casting operation.[4–9] Although these investigations have effectively improved the casting performance of the mold flux, the layering behavior of the slag infiltration during mold oscillation has not yet been considered, which causes inhomogeneity of the chemical composition in the liquid pool and interfacial gap, resulting in inadequate lubrication and unstable heat transfer in plant practice. In the conventional continuous casting of steel, mold powder is added to the top surface of the steel and forms several layers, including a powder, sinter, mushy, and liquid layer. The liquid slag infiltrates into the gap between the shell and mold, forming two slag films. The solid film controls the horizontal heat transfer, whereas the liquid film is responsible for lubrication of the shell. Therefore, the surface quality of the steel depends greatly on the slag properties and casting parameters. For example, the viscosity of the mold flux is one of the most important properties because it determines the powder consumption and therefore the shell lubrication, and the break temperature determines the thicknesses of the solid and liquid layers in the gap.[10–12] On the other hand, casting speed is the most obvious parameter
affecting slag infiltration; for instance, slag consumption decreases with higher casting speed.[13,14] Mold oscillation controls the friction force between the solidified shell and the mold wall, accompanying with the slag consumption and oscillation mark formation.[15–17] These combined factors are difficult to predict and control during the continuous
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