Numerical Modeling of Macrosegregation in Round Billet with Different Microsegregation Models

Abstract

A macrosegregation model, coupling fluid flow, heat and solute transport model, was developed based on continuum model to predict the evolution of macrosegregation in continuous round billet casting, as well as the influence of microsegregation model choice on prediction of macrosegregation. Evolution and characteristics of macrosegregation corresponding to predicted solidification were revealed. As solidification proceeds, solutes are ejected from solid phase to liquid at solidification front. The resulting mushy zone is enriched by solutes, due to the low velocity and limited diffusion, which produces segregation at the billet center as the liquid available for dilution diminishes near the end of solidification. Predicted and experimental results for surface temperature and centerline segregation compare agreeably, which indicates the validity of the coupled macrosegregation model in this work. A detailed analysis was performed to investigate the influence of microsegregation model on prediction of macrosegregation, demonstrating that choice of model affects predicted segregation degree of solutes, which effect varies with type of solute, due to the solute back-diffusion coefficient.

Three-Dimensional Numerical Modeling of Macrosegregation in Continuously Cast Billets

“…The segregation profiles showed no evident distinction between the two plotted locations for both sections, although the central liquid fraction was predicted to be about 0.2 at the Z = 9.1 m plane. This suggests that macrosegregation in the billet formed in the mushy zone with relatively low central liquid fraction, but not the region near the sump bottom and this corresponds with the conclusion reported in previous study [24]. Comparison between the segregation profiles of the two sections (longitudinal and diagonal) reveals the similar features in the distribution of solute C. The simulation results indicate that the highest segregation degree (positive segregation) occurred at the central region of billet, while relatively low values of segregation degree (negative segregation) are predicted at either side of the center.…”

“…The macrosegregation model was solved in the computational domain shown in Figure 1 with the appropriate initial conditions, boundary conditions, and thermophysical parameters in open-source software OpenFOAM; details of the conditions can be found in previous work [24]. The high-carbon steel SWRH82B is used in this study, the chemical composition and corresponding diffusion coefficients are listed in Table 2 along with the equilibrium partition coefficients of each element, and the thermophysical parameters of the steel are listed in Table 3.…”

“…The distinction between the calculated solid fraction and theoretical value would cause some effects on the magnitude of segregation. To discuss this, other two two-dimensional calculations [24] were performed with the linear f s − T function (Equation (12)) and nonlinear f s − T relation (Equation (36)) separately. In the calculation, the partition coefficient in Equation (36) is determined to be 0.34, and the back-diffusion coefficient is set to be 0.9 according to the calculated values of solute C. As noted already, the coefficients are different for various solute elements.…”

Prediction of Central Carbon Segregation in Continuous Casting Billet Using A Regularized Extreme Learning Machine Model

“…% X 5 Sulfur content in molten steel wt. % X 6 Secondary cooling water flow rate in zone1 L/min X 7 Secondary cooling water flow rate in zone2 L/min X 8 Secondary cooling water flow rate in zone3 L/min X 9 Secondary cooling intensity L/kg X 10 Pouring temperature • C X 11 Casting speed m/min X 12 Superheat • C X 13 Mold water flow rate L/min X 14 Mold water temperature difference • C Figure 2. Schematic diagrams of sampling (a) and drilling (b) in the steel billets.…”

“…The metallurgical mechanism methods involve establishing the functional relationship between process parameters and central carbon segregation, and determining the segregation level. Many scholars have made contributions in this aspect especially by means of numerical simulation [6][7][8][9]. Numerical models are powerful tools which are capable of capturing the overall segregation evolution with good visualization.…”