Numerical Simulation of V-shaped Segregation in Continuous Casting Blooms Based on a Microsegregation Model
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BLOOM macrosegregation leads to nonuniformity in the mechanical properties of the final products that cannot be alleviated by the subsequent heat treatment and rolling process.[1–4] The primary techniques for reducing macrosegregation are low-superheat casting,[5] soft reduction,[6] intensive cooling at the solidification end,[7] and electromagnetic stirring.[8] Among these, low-superheat casting and intensive cooling at the solidification end are the most convenient and economical methods to improve macrosegregation, and mechanical reduction has proved to be the most effective countermeasure to prevent bloom macrosegregation, particularly V-shaped segregation. Numerous scientific studies[9–32] have sought to investigate the control method and formation mechanism of bloom macrosegregation. Miyazawa and Schwerdtfeger[9] studied the macrosegregation caused by bulging and revealed the main mechanism of centerline macrosegregation. Kajitani et al.[10] simulated the deformation-induced macrosegregation in continuous casting. Wu et al.[11,12] researched the principle of mechanical soft reduction on centerline segregation for a binary Fe-C alloy. The author[6] presented a soft reduction amount calculation model to improve centerline segregation and V-shaped RUI GUAN, CHENG JI, MIAOYONG ZHU, and SHIMIN DENG are with the School of Metallurgy, Northeastern University, 311, Wenhua Road, Shenyang 110816, China. Contact e-mail: [email protected] Manuscript submitted January 2, 2018.
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segregation. To further optimize this model, the author gradually realized that fluid flow, macro-scale heat transfer, and solute transport with back diffusion are the common factors affecting bloom macrosegregation. In the late 1960s, Flemings et al.[13–15] established the local solute redistribution segregation model. Subsequently, Bennon and Incropera[16,17] proposed a continuous model to couple energy, momentum, and solute transport. During the same period, Beckermann et al.[18–20] developed a volume-averaged model to research the effects of the transport phenomena and microstructure on macrosegregation. Wu et al.[21,22] introduced a Eulerian model to describe multiphase and multiscale macrosegregation behavior. El-Bealy[23] investigated the formation mechanism of macrosegregation based on the work of Flemings, Nereo,[13] and Beckermann.[18–20] In previous work, the author[24] demonstrated that superheat and the solidification structure strongly affect the formation of segregation by combining the microstructure with macrosegregation model. Due to the enormous computational burden, the segregation models used in the above research works have largely been based on the Lever rule and Scheil model. In reality, the influence of back diffusion in the solid phase results in a solute distribution in between those predicted by the Lever rule and Scheil model, which can in turn affect the accuracy of macrosegregation predictions. Back diffusion has been introduced into many microsegregation models. Brody and Flemings[25
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