Shear-thinning behavior of the CaO–SiO₂–CaF₂–Si₃N₄ system mold flux and its practical application

Abstract

Satisfying the mold-flux performance requirements for high-speed continuous casting necessitates the development of a new non-Newtonian-fluid mold flux with shear-thinning behavior, i.e., a mold flux whose viscosity is relatively high under lower shear rates and relatively low under higher shear rates. In this work, a mold flux that exhibits shear-thinning behavior was developed by adding different amounts of Si3N4 to the CaO–SiO₂–CaF₂ mold flux. The shear-thinning behavior was investigated using a rotational viscometer. In addition, the microstructure of the newly prepared slags was studied by high-temperature Raman spectroscopy and X-ray photoelectron spectroscopy. The results showed that the mechanism of shear-thinning was attributable to a temporary viscosity loss caused by the one-way shear stress, whereas the corresponding magnitude of shear-thinning was closely related to the degree of polymerization (DP). Finally, the non-Newtonian fluid mold flux was used for laboratory casting tests, which revealed that the mold flux could reduce slag entrapment and positively affect the continuous casting optimization.

Keywords

mold flux / viscosity / shear-thinning behavior / non-Newtonian fluid / degree of polymerization

References

[1] Suzuki M., Miyahara S., Kitagawa T., Uchida S., Mori T., Okimoto K. Effect of mold oscillation curves on heat transfer and lubrication behaviour in mold at high speed continuous casting of steel slabs. Tetsu-to-Hagane, 2009, 78(1): 113.

[2] Nakajima K., Hiraki S., Kawamoto M., Kanazawa T. Melting, lubrication, and heat transfer behavior of mold powder in mold at high speed continuous casting of steel slabs. Sumitomo Met., 1993, 45(3): 8.

[3] Saraswat R., Fox A.B., Mills K.C., Lee P.D., Deo B. The factors affecting powder consumption of mould fluxes. Scand. J. Metall., 2004, 33(2): 85.

[4] Shin S.H., Yoon D.W., Cho J.W., Kim S.H. Controlling shear thinning property of lime silica based mold flux system with borate additive at 1623 K. J. Non-Cryst. Solids, 2015, 425, 83.

[5] Watanabe K., Tsutsumi K., Suzuki M., Fujita H., Hatori S., Suzuki T., Omoto T. Development of new mold flux for continuous casting based on non-Newtonian fluid properties. ISIJ Int., 2014, 54(4): 865.

[6] Kanazawa T., Hiraki S., Kawamoto M., Nakai K., Hanazaki K., Murakami T. Behavior of lubrication and heat transfer in mold at high speed continuous casting. Tetsu-to-Hagane., 1997, 83(11): 701.

[7] Nakato H., Omiya S., Habu Y., Emi T., Hamagami K., Koshikawa T. Optimizing mold lubrication for high-speed continuous casting of slabs. JOM, 1984, 36(3): 44.

[8] Watanabe K., Tsutsumi K., Suzuki M., Nakada M., Shiomi T. Effect of properties of mold powder entrapped into molten steel in a continuous casting process. ISIJ Int., 2009, 49(8): 1161.

[9] Mills K.C., Fox A.B. The role of mould fluxes in continuous casting-so simple yet so complex. ISIJ Int., 2003, 43(10): 1479.

[10] Shin S.H., Cho J.W., Kim S.H. Shear thinning behavior of calcium silicate-based mold fluxes at 1623 K. J. Am. Ceram. Soc., 2014, 97(10): 3263.

[11] Shin S.H., Cho J.W., Kim S.H. Controlling the shear thinning property of calcium silicate melts by addition of Si3N4. J. Non-Cryst. Solids, 2015, 423-424, 45.

[12] He Y.R., Men Y.B., Liu X., Lu H.L., Chen H.S., Ding Y.L. Study on forced convective heat transfer of non-Newtonian nanofluids. J. Therm. Sci., 2009, 18(1): 20.

[13] Gu Y., Liu R.Z., Wu K., Zhao Y., Li S.Q., Gao X., Sun G.J. A study on rheologic characteristics of mold fluxes for high speed continuous casting. Spec. Steel, 2004, 25(1): 18.

[14] Peng Y., Lv B.H., Yuan J.L., Ji H.B., Sun L., Dong C.C. Application and prospect of non-Newtonian fluid in the industrial field. Mater. Sci. Forum, 2014, 770, 396.

[15] Liu H.Y., Pang M.G., Wei J.J. A progress and trend of the non-Newtonian fluids. Appl. Chem. Ind., 2010, 39(5): 740.

[16] Zhu K.Q. Some advances in non-Newtonian fluid mechanics. Mech. Eng., 2006, 28(4): 1.

[17] Shin S.H., Cho J.W., Kim S.H. Structural investigations of CaO–CaF₂–SiO₂–Si₃N₄ based glasses by Raman spectroscopy and XPS considering its application to continuous casting of steels. Mater. Des., 2015, 76, 1.

[18] Chiellini E., Giordano M., Leporini D. Structure and Transport Properties in Organized Polymeric Materials, 1998, Pisa, World Scientific Publishing Company 348.

[19] Swenson J., Börjessonb L. Intermediate-range structure and conductivity of fast ion-conducting borate glasses. J. Non-Cryst. Solids, 1998, 232-234, 658.

[20] Bachar A., Mercier C., Tricoteaux A., Leriche A., Follet C., Saadi M., Hampshire S. Effects of addition of nitrogen on bioglass properties and structure. J. Non-Cryst. Solids., 2012, 358(3): 693.

[21] Dolekcekic E., Pomerpocy M.J., Hampshire S. Structural characterisation of Er-Si-Al-O-N glasses by Raman spectroscopy. J. Eur. Ceram. Soc., 2007, 27(2-3): 893.

[22] Park J.H. Structure–property relationship of CaO–MgO–SiO₂ slag: quantitative analysis of Raman spectra. Metall. Mater. Trans. B, 2013, 44(4): 938.

[23] Park J.H. Effect of silicate structure on thermodynamic properties of calcium silicate melts: quantitative analysis of Raman spectra. Met. Mater. Int., 2013, 19(3): 577.

[24] Das T. Oxynitride glasses–An overview. Bull. Mater. Sci., 2000, 23(6): 499.

[25] Yun H.J., Lee J., Jung M.C., Han M.S., Park K., Ahn K.S., Choi C.J. Chemical bonding structures of silicon oxynitride films grown by ionized N2 and pure O2 gas mixtures at low temperature. Adv. Appl. Ceram., 2011, 110(1): 25.

[26] Rudnick L.R. Lubricant Additives: Chemistry and Applications, 2009 56.