Analysis on the Deflection Angle of Columnar Dendrites of Continuous Casting Steel Billets Under the Influence of Mold E
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S casting (CC) of steel is a complex process that involves heat transfer, fluid flow, and solidification, which in some cases occurs under an electromagnetic (EM) field.[1] EM fields are applied to achieve a better product quality and a higher productivity in the industry by generating the swirling flow.[2] The quality and property of continuous casting products are strongly related to the microstructure developed during solidification. The solidification microstructure can generally be categorized into a chilled layer zone, columnar zone, columnar-to-equiaxed transition (CET) zone, and equiaxed zone. The size of these zones is affected by many factors including superheat, casting speed, cooling rate, and EM fields.[3] The application of EM field provides a considerable potential to control the fluid flow of the molten steel in the mold. Mold electromagnetic stirring (M-EMS) can enhance the area fraction of the CET in the billet XINCHENG WANG, Ph.D. Student, SHENGQIAN WANG, Postdoctoral Fellow, and LIFENG ZHANG, Professor, are with the Beijing Key Laboratory of Green Recycling and Extraction of Metals (GREM) and the School of Metallurgical and Ecological Engineering at the University of Science and Technology Beijing (USTB), Beijing 100083, China. Contact e-mail: [email protected] SEETHARAMAN SRIDHAR, RAEng/TATA Steel Chair and Director, is with the Advanced Steel Research Centre, WMG, University of Warwick, Coventry, CV47AL, U.K. ALBERTO CONEJO, Visiting Professor, is with the Morelia Technological Institute, Morelia 58120 Me´xico, and also with the University of Science and Technology Beijing (USTB). XUEFENG LIU, Professor, is with the School of Materials Science and Engineering at University of Science and Technology Beijing (USTB). Manuscript submitted March 3, 2016. Article published online August 24, 2016 5496—VOLUME 47A, NOVEMBER 2016
compared to without M-EMS during solidification.[4] The frequency of M-EMS has little effect on the electromagnetic torque, but the current intensity has great influence. The equiaxed crystal ratio increases by 0.159 when increasing the torque from 230 to 400 cN cm.[5] The normal growth direction of columnar dendrites is in the direction of extraction of heat in the mold. Three driving forces control crystal growth: thermal gradients, concentration gradients, and momentum gradients. A higher driving force around the tip of the columnar dendrite defines the direction of growth. Since the 1980s, deflection of columnar dendrite from its normal growth direction has frequently been observed in the presence of liquid flow in front of the solid–liquid interface during solidification.[6–13] The deflection angle was found to be the result of solute depletion in the upstream direction and higher solute concentration in the downstream direction due to convective flow around the tip of the columnar crystals.[12,14,15] In these conditions, the concentration gradient increases in the upstream direction. A deflection angle from 6 to 12 deg was reported during the solidification of an Al-Cu alloy due to an increase in l
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