Optimization of Mold Flux for the Continuous Casting of Cr-Contained Steels
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Optimization of Mold Flux for the Continuous Casting of Cr-Contained Steels WANLIN WANG, JIE YU, LEJUN ZHOU, ZHAOYANG WU, and HUAN LI To compensate the negative effect caused by the absorption of chromium oxide inclusions during the casting process of Cr-contained steels, a new mold flux system has been designed and investigated. The melting temperature range of the newly designed mold flux system is from [1124 K to 1395 K (851 °C to 1122 °C)]. The viscosity at 1573 K (1300 °C) and the break temperature increase with the addition of MnO and Cr2O3 but decrease with the addition of B2O3. The crystalline fraction of mold flux decreases from 81 to 42.1 pct with the addition of MnO and Cr2O3, and then further decreases to 25.3 pct with the addition of B2O3; however, it improves from 54.4 to 81.5 pct when the basicity increases. Besides, the heat-transfer ability of mold flux is inverse to the crystallization ratio of the slag. The comprehensive study of the properties for the four designed mold fluxes suggests that the mold flux with 1.15 basicity-3.01 pct B2O3-1.10 pct MnO-2.10 pct Cr2O3 shows the best properties for the continuous casting of Cr-contained steels. https://doi.org/10.1007/s11663-018-1279-7 Ó The Minerals, Metals & Materials Society and ASM International 2018
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INTRODUCTION
MOLD flux has been widely used in the continuous casting process, which can absorb inclusions and insulate molten steel from oxidation when it floats on the top of the molten steel. It also tends to lubricate the strand and moderate the horizontal heat transfer in the mold when it infiltrates into the gap between the mold wall and solidified shell. During the metallurgical process of Cr-contained steels, such as Cr12MoV, the alloy element Cr in molten steel is easy to be oxidized during the smelting, refining, and continuous casting processes, as it has a closer affinity with oxygen than Fe.[1–3] Those Cr oxide inclusions would float up into the liquid mold flux under the overall forces exerted by buoyancy, fluid flow, bubbles, etc.[4–6] Then, the performance of the mold flux will be deteriorated with the pickup of chromium oxides in the liquid slag, which, in turn, leads to the defects occurring on both the surface and interior of the final strand. Khater and Idris[7] investigated the effect of Cr2O3 on the melting temperature and crystallization of aluminosilicate glass and found that Cr2O3 tends to
WANLIN WANG, JIE YU, LEJUN ZHOU, and HUAN LI are with the School of Metallurgy and Environment, Central South University, Changsha 410083, P.R. China. Contact email: [email protected] ZHAOYANG WU is with the Key Laboratory of Metallurgical Emission Reduction & Resources Recycling, Anhui University of Technology, Ma’anshan 243002, P.R. China. Manuscript submitted July 28, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
increase the melting temperature and enhance the crystallization of the glass. Marghussian and Arjomandnia[8] studied the crystallization behavior of glassy ceramics in the presence of Cr2O3 nucleates and suggested that the crystalliz
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