Numerical modeling of centerline segregation by a combined 3-D and 2-D hybrid model during slab continuous casting
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Centerline segregation is one of the typical internal defects, which occurs during slab continuous casting (CC). To investigate and predict the centerline segregation encountered in a continuously cast slab, a combined 3-D and 2-D hybrid simulation model for centerline segregation was developed. The average deviation between the calculated and experimented results reaches as low as 0.5%, which demonstrates that the hybrid simulation model has relatively high reliability. The centerline segregation of the slab was predicted accurately. The results show that macrosegregation occurring during the slab CC process has heredity. In the casting direction, the concentration of solutes in the liquid pool increases gradually until the casting has solidified completely. After complete solidification, the solutes’ concentration maintains an almost constant value. On the centerline, the maximum segregation degree occurs at a position roughly 614 mm from the slab center. The maximum centerline segregation degrees of C, Si, Mn, P, and S solutes are 1.163, 1.058, 1.045, 1.111, and 1.165, respectively.
I. INTRODUCTION
Centerline segregation occurs in the central zone of cast slabs, where impurity and solute element concentrations are extraordinarily high, and is a serious internal defect encountered during slab continuous casting (CC). Unfortunately, such a macroscale internal defect is impossible to eliminate completely by subsequent hot working processes and will be inherited in the final steel products. The heredity of centerline segregation leads to the nonuniform distribution of solutes and eventually to heterogeneous mechanical properties in produced steel products, resulting in poor product quality. Therefore, an in-depth understanding of the formation mechanism behind centerline segregation is needed to homogenize solute distribution and improve the mechanical performance of steel products. Compared with experiments, numerical modeling has a higher efficiency and can provide large amounts of transitional information, which is very important to explore and reveal the formation mechanism behind some phenomena. Centerline segregation, which occurs in complex CC processes, is closely related to the transitional information during CC, such as fluid convection, solute redistribution in the mushy zone, and solidification rate.1–3 This means that a verified numerical model is more appropriate for studying and obtaining Contributing Editor: Susan B. Sinnott Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2018.23
a thorough understanding of centerline segregation to optimize the CC process and improve strand quality. To date, the macrosegregation model applied in alloy solidification processes originates from the model proposed by Flemings et al. in 1967.4,5 In the mathematical model for macrosegregation, the fluid flow in the mushy zone is related to the permeability and is described by Darcy’s law.6 To consider the solute redistribution at the microscale, a contin
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