Center Segregation with Final Electromagnetic Stirring in Billet Continuous Casting Process
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DUE to the solubility difference between liquid and solid phases, solute element is rejected from dendrite and accumulates in the interdendritic melt. With the effect of forced or natural convection, the rejected solute element is carried away, resulting in the formation of macrosegregation.[1,2] As the diffusing time is so long in practice, macrosegregation cannot be eliminated in the subsequent heat treatment and affects product mechanical property. In the past few decades, many techniques have been proposed to minimized strand macrosegregation, such as low temperature casting, soft reduction, intensive cooling at the solidification end, and electromagnetic stirring (EMS).[3] Among those techniques, EMS is one of the widely used methods and much effort has been devoted to investigate fluid flow on macrosegregation improvement, both in the experiment and simulation area. Mizukami et al.[4] carried out experiments in laboratory scale ingot casting and found V-segregation could be eliminated by the EMS at the later stage of solidification, while sufficient amount of equiaxed grains was an essential condition. Ayata et al.[5] undertook plant trials and laboratory experiments to investigate EMS mode on macrosegregation improvement. The
DONGBIN JIANG and MIAOYONG ZHU are with the School of Metallurgy, Northeastern University, Shenyang 110819, China. Contact e-mail: [email protected] Manuscript submitted July 17, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
center segregation could be reduced by the combination of mold and final electromagnetic stirring (M-EMS and F-EMS), and the optimum stirring condition existed for F-EMS. Suzuki et al.[6] applied some EMS experiments in small ingot casting and found V-segregation could be improved by weak stirring, while intensive stirring had some detrimental effects. Du et al.[7] conducted plant tests to investigate EMS mode on bloom segregation improvement and found that the combination of M-EMS and alternative F-EMS was the best stirring mode. In these studies, plant trials or laboratory experiments were undertaken to investigate EMS on macrosegregation improvement, but the segregation evolution with forced convection during solidification process was difficult to observe. So many researchers[8–11] applied numerical models to simulate fluid flow and solute transport behavior during solidification process. Luo et al.[8] studied the distribution of electromagnetic field and flow field in final stirring zone, and some plant trials were also carried out to obtain the optimum stirring parameters. The liquid flow in the F-EMS zone was studied and the center segregation could reach the lowest level with optimum current intensity, whereas the solidification behavior was not considered. With the Darcy’s law introduced to consider solidification effect, Ren et al.[9] applied the continuum model to analyze the fluid flow and solidification behavior with M-EMS. It was found that the melt residence time in the mold was prolonged and the superheat dissipation was accelerated, which were benefits for the equia
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