Crystallization Characteristics of CaO-Al 2 O 3 -Based Mold Flux and Their Effects on In-Mold Performance during High-Al
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icity (TRIP) steels exhibit great applications in automobile industry due to their excellent combination of high strength and superior formability.[1,2] Considering the additional advantages (i.e., improving galvanizability,[2,3] effectively suppressing the surface oxide layer formation induced by high silicon content in the steel,[4,5] and optimizing the TRIP effect during straining[6]) contributed by partial substitution of silicon by aluminum in conventional TRIP steels, high-aluminum TRIP steels have been receiving great attention. However, the change in the chemistry of conventional lime-silicabased mold fluxes resulting from the reduction of SiO2 in mold flux by aluminum in molten steel has always CHENG-BIN SHI, Postdoctoral Fellow, MYUNG-DUK SEO, Ph.D. Candidate, and SEON-HYO KIM, Professor, are with the Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Republic of Korea. JUNG-WOOK CHO, Research Associate Professor, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted December 9, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
been one of the extremely serious issues in continuous casting of high-aluminum TRIP steels.[7–10] This variation generally causes the instability of viscosity and other thermophysical properties of mold flux, which has been reported as the principal reasons for various problems during casting of high-Al steels such as breakout, nonuniform heat transfer across mold flux, inadequate lubrication, and poor as-cast slab surface quality, etc.[8–10] In view of the above aspects, it is in urgent need to develop optimal mold fluxes to meet the requirements of high-aluminum steels casting. In recent years, several efforts have been made to explore substitutes for conventional lime-silica-based mold fluxes.[9,11,12] With the main focus on minimization of the interaction between mold flux and molten steel, Blazek et al.[9] developed lime-alumina-based mold flux for casting high-aluminum TRIP steel, and the production trials showed that the interaction was markedly reduced and the as-cast slab quality was improved compared with lime-silica-based mold flux, while the mold flux consumption and lubrication remained to be improved. In a more recent study, Cho et al.[11] carried out casting trials of TRIP steel containing 1.45 mass pct Al by using the newly developed lime-alumina-based mold fluxes, and the results showed that the lubrication and mold heat
transfer in casting process and surface quality of slab were improved, compared with that of lime-silica-based mold fluxes. Wu et al.[12] reported, based on laboratory experimental results, that the crystalline phases of the developed lime-alumina-based mold fluxes were mainly 12CaOÆ7Al2O3 and 11CaOÆ7Al2O3ÆCaF2, and suggested that 12CaOÆ7Al2O3 exhibited great potential as a substitute for cuspidine (3CaOÆ2SiO2ÆCaF2). However, only a few studies reg
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