Mechanism of Macrosegregation Formation in Continuous Casting Slab: A Numerical Simulation Study
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d steel solidification, the solute element is rejected from the solid dendrite and enriches in the interdendritic melt. With the effect of fluid flow, the rejected solute element is carried away and transported a long distance, leading to the macrosegregation formation.[1] In the past few decades, many different theories have been provided to explain the reasons for center segregation in the continuously casting strand, such as the thermosolutal convection,[2–4] the grain sedimentation,[4] the shell bulging,[5–7] the grain bridging and solidification shrinkage,[8,9] and the thermal shrinkage.[10,11] Due to the density difference caused by thermal and solute gradients, the liquid steel is forced to move, leading to thermosolutal convection. In this aspect, Aboutalebi et al.[2] applied the continuum model to DONGBIN JIANG, WEILING WANG, SEN LUO, CHENG JI, and MIAOYONG ZHU are with the School of Metallurgy, Northeastern University, Shenyang 110819, China. Contact e-mail: [email protected] Manuscript submitted May 22, 2017.
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investigate solute transport in the billet continuous casting and found the solute concentration increasing continuously to the strand center. Sun and Zhang[3] also studied the thermosolutal convection and observed an irregular positive segregation near the bloom center, while the negative segregation in the periphery zone was not obtained. Jiang and Zhu[4] developed a multiphase solidification model to simulate solute transport and solidification structure in the billet continuous casting process. It was found that the negative segregation around positive segregation was created by grain sedimentation and thermosolutal flow, while the calculated data in the periphery zone were clearly larger than the measured data. For the shell bulging, Miyazawa and Schwerdtfeger[5] investigated the fluid flow with solid deformation and observed that center segregation increased obviously as the slab passed the supporting roller. Subsequently, Kajitani et al.[6] simulated the solid deformation and interdendritic flow between several supporting rollers. It was demonstrated that the shell bulging-compression sequence contributed to center segregation. Mayer et al.[7] studied the liquid flow induced by shell bulging and solidification shrinkage. They also found that the center segregation was dominated by shell bulging. However, Murao et al.[8] did not
think the shell bulging was a necessary condition for center segregation and held the grain bridging and solidification shrinkage were the main reasons. As the grains bridging formed in the strand, the concentrated liquid was sucked to the center by solidification shrinkage, resulting in the positive segregation. Based on plant trails, Suzuki[9] observed the positive segregation was beneath the grains bridging in the etched strand sample. Except the viewpoint discussed previously, Janssen et al.[10] also did not believe the center segregation was caused by shell bulging and proposed the thermal shrinkage theory. With a freely deformed tu
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