A coupled model on fluid flow, heat transfer and solidification in continuous casting mold

Abstract

Fluid flow, heat transfer and solidification of steel in the mold are so complex but crucial, determining the surface quality of the continuous casting slab. In the current study, a 2D numerical model was established by Fluent software to simulate the fluid flow, heat transfer and solidification of the steel in the mold. The VOF model and k-ε model were applied to simulate the flow field of the three phases (steel, slag and air), and solidification model was used to simulate the solidification process. The phenomena at the meniscus were also explored through interfacial tension between the liquid steel and slag as well as the mold oscillation. The model included a 20 mm thick mold to clarify the heat transfer and the temperature distribution of the mold. The simulation results show that the liquid steel flows as upper backflow and lower backflow in the mold, and that a small circulation forms at the meniscus. The liquid slag flows away from the corner at the meniscus or infiltrates into the gap between the mold and the shell with the mold oscillating at the negative strip stage or at the positive strip stage. The simulated pitch and the depth of oscillation marks approximate to the theoretical pitch and measured depth on the slab. https://doi.org/10.1007/s41230-017-7171-2 I n the continuous casting process of the slab, many complex phenomena [1][2][3] occur in the mold, including fluid flow, heat transfer, steel solidification, interaction between steel and slag [4] , etc. The liquid steel flows into the mold cavity through the submerged entry nozzle (SEN) and then solidifies against the four walls of the water-cooling copper mold. The solidified shell is continuously withdrawn downward at the casting speed. The slag powder is continuously added on the top of the steel, then melts or sinters to form a slag bed, and liquid slag infiltrates into the gap between the shell and the mold [5,6] . Due to the interfacial tension, a curved meniscus [7] forms between liquid steel and liquid slag, and solidifies with the heat transfer from the steel to the mold. Heat transfer and solidification of the liquid steel at the meniscus as well as the mold oscillation affect the formation of the oscillation marks [8] , which may cause some defects in the slab, including slag entrapment [9] , bubble and inclusion capture, element segregation, transverse cracks [10] , etc. In the current study, a 2D model was established to simulate the multiphase fluid flow of steel-slagair, heat transfer and solidification in the mold with mold oscillation. The model considered the interfacial tension between different phases and shell movement at the casting speed. The phase distribution and flow field in the mold were simulated, and phenomena near the meniscus were presented, including meniscus solidification, slag penetration and movement of the mold and the shell. The comparison of simulated pitch and depth of oscillation marks with theoretical pitch and measured depth on the slab surface was conducted to validate the accuracy of the...

Influence of Interfacial Thermal Resistance on Initial Solidification and Heat Transfer in Continuous Casting Mold of Steel

“…[23,28,34] During the calculation of the 2D mold model, over 1 month was consumed to achieve stability of each case with the time step of 5 Â 10 À5 s and the eight-core computer. To validate the accuracy of the simulation, the shape of the solidified meniscus from the simulation and the curved hook measured from the slab [34] was compared, and the depth of oscillation marks through simulation and measurement with the same casting condition was also compared in the study by Zhang et al [37] and in Figure 8a later. The depth of the slag in the gap was below 1.5 mm in Figure 4b, which was consistent with results reported.…”

Mathematical Modeling on Slag Consumption and Lubrication in a Slab Continuous Casting Mold

“…In the current study, the two-dimensional mathematical model [32,33] was applied to investigate the slag lubrication in continuous casting mold of slab. The fluid flow of steel-slag-air three phases, heat transfer of the fluid and the copper plate, and the solidification of the steel were considered through the adoption of the realizable k-e model, volume of fluid (VOF) model and solidification model, and the coupled solution of governing equations including the continuity equation, Navier-Stokes equations, and the energy equation.…”

“…[33] According to the continuous casting of the low-carbon steel in a steel plant, simulation parameters in the current study were shown in Table I, and other details were described elsewhere. [8,32,33] During the simulation, several locations were monitored to obtain the thickness, the velocity, and the consumption of the slag in the shell/mold gap, and the schematic of phase distribution and monitor locations are shown in Figure 1. Horizontal coordinates and the vertical velocity on the steel-slag interface (Density = 5000 kg/m 3 ) and the solid-liquid slag interface (g=20 P) in the shell/mold gap and the consumption of the total slag were monitored at 10, 40, 100, and 300 mm below meniscus, shown as white dotted lines in Figure 1.…”

“…The periodic pressure and liquid-slag layer thickness in the flux channel for the upper and lower meniscus and the meniscus behavior during the cast start of the steel were described by Yang and Zhu et al [22,31] through an experimental cold model and a 2D coupled model. In 2017-2019, the author and Zhang [8,32,33] employed a coupled 2D model to predict the initial solidification and slag infiltration and compare the influence of different casting parameters on meniscus solidification and shell thickness.…”

Construction of Nonsinusoidal Oscillation Waveform Function and Technological Parameters for Continuous Casting Mold

“…Nowadays, mold oscillation technologies used in production mainly include sinusoidal and nonsinusoidal oscillations. Sinusoidal oscillation could reduce negative strip time and improve surface quality of slab when high frequency and small amplitude operation are adopted [5,6]. Lin et al [7] optimized the sinusoidal oscillation parameters for Nanjing steel, the lubrication between the mold and slab had been improved, the demoulding resistance was reduced, the hook-type oscillation mark was eliminated, and the slab quality was enhanced.…”