Effects of MnO on Crystallization, Melting, and Heat Transfer of CaO-Al 2 O 3 -Based Mold Flux Used for High Al-TRIP Ste
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IN past decades, high aluminum containing steels have been produced through continuous casting. It is well known that the high Al concentration in the steels inclines to react with SiO2 and other less stable oxides (MnO, FeOx, etc.) in the conventional lime-silica bases mold fluxes during casting,[1–4] which causes the poor inmold performance of mold fluxes, such as sticking of the mold flux to copper mold, increase of crack frequency due to lubrication issue, etc. Considerable efforts have been carried out to solve these problems by optimizing the ratio of CaO/SiO2[5,6] or Al2O3/SiO2[4,7] or the amount of fluidizers[8,9] for the lime-silica-based flux, but it is difficult to find an optimal composition for high Al grade steel due to the slag/steel interface reactions. Recently, a series of lime-alumina-based mold fluxes for high Al grade steels has been developed. Unlike the compositions of conventional lime-silica-based mold fluxes, SiO2 was partly replaced by Al2O3 in the newly developed mold fluxes for inhibiting the slag/steel interaction. Several casting trials[10] have been carried out for high Al grade steels using the lime-aluminabased mold fluxes; the results of these tests show that the slag/steel interaction was obviously inhibited and the ascast slab surface quality improved markedly, but the
HUAN ZHAO and BOXUN LU, Graduate Students, WANLIN WANG, Professor, and LEJUN ZHOU, Post Doctor, are with the School of Metallurgical Science and Engineering, Central South University, Changsha, Hunan, 410083, P.R. China. Contact e-mail: [email protected] YOUN-BAE KANG, Assistant Professor, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang, Gyeongbuk, 740-748, South Korea. Manuscript submitted December 18, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
slag film were prone to crystallize easily during casting, which made the mold lubrication deteriorate rapidly. To improve the in-mold performance of lime-alumina-based mold fluxes, intensive studies regarding the effects of fluxing agents (CaF2, Na2O, Li2O, B2O3, etc.) on properties and performance of those mold fluxes have being studied. Yu[11] studied the physical properties of lime-alumina-based mold fluxes with different CaF2 content; the results show that CaF2 could decrease the viscosity and melting temperature and promote the crystallization behavior of the mold flux. Wang et al.[12] found that Na2O could enhance the heat transfer of nonreactive mold fluxes through restraining the crystallization. The results of cast trials conducted by Cho et al.[10] suggested that Li2O and B2O3 greatly retard the crystallization of lime-alumina-based mold fluxes. Similar results were also obtained by Blazek et al.[1]; in addition, his research suggested that B picked up in steel as B2O3 in mold flux reduced by [Al]. However, the consumption and poor lubrication problems have not been solved effectively by adding the fluxing agents as mentioned earlier. As an important fluxing agent in conventional limesilica-based mold flux, MnO is u
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