Effect of SEN immersion depth on mold flow profile and slag entrapment during continuous casting of steel

Mold flux entrapment during continuous casting of steel contributes to both surface and sub-surface defects in the final product. Continuous casting operating parameters such as casting speed, SEN immersion depth, SEN port geometry, argon flow, and mold EMS significantly affect the mold flow conditions and flow profile. During continuous casting operation, SEN immersion depth is continuously varied to avoid localized erosion of SEN, and it impacts the flow dynamics in the mold. In the present work, water modeling studies were carried out for a wide range of mold widths (1200-1800 mm) and casting speeds (0.8-1.4 m/min) on a 0.5 scaled down water model to optimize casting speed for different combinations of SEN immersion depth and mold width. Results from water modeling were further validated using nail board studies in the actual plant. A safe operating matrix was identified from these experiments to avoid mold slag entrapment during continuous casting.

Modeling of the BOF Tapping Process: The Reactions in the Ladle

A tapping process model of the steel from the basic oxygen furnace (BOF) addressing the reactions in the ladle is proposed. In the model, the effective equilibrium reaction zone (EERZ) method is applied to describe the steel/slag interfacial reaction. The equilibrium reactions in the bulk steel (steel/inclusion/lining wear) and slag (liquid slag/slag additions/lining wear) are considered. The thermodynamic library—ChemApp is used to perform thermodynamic calculation. The process model includes most of the actions during the tapping process, such as the additions of ferroalloys and slag formers, carryover slag entrapment and air pick-up. After the calibration by the industrial measurements of two plants, the model is applied to study the influence of the amount of carryover slag.

Large Eddy Simulation of Multi-Phase Flow and Slag Entrapment in Molds with Different Widths

Slag entrapment is a critical problem that affects the quality of steel. In this work, a three-dimensional model is established to simulate the slag entrapment phenomenon, mainly focusing on the slag entrapment phenomenon at the interface between slag and steel in molds with different widths. The large eddy simulation (LES) model and discrete particle model (DPM) are used to simulate the movements of bubbles. The interactions between phases involve two-way coupling. The accuracy of our mathematical model is validated by comparing slag–metal interface fluctuations with practical measurements. The results reveal that the average interface velocity and transverse velocity decrease as the mold width increases, however, they cannot represent the severity of slag entrapment at the interface between slag and steel. Due to the influence of bubble motion behavior, the maximum interface velocity increases with mold width and causes slag entrapment readily, which can reflect the severity of slag entrapment. On this basis, by monitoring the change of impact depths in different molds, a new dimensionless number “C” is found to reveal the severity of slag entrapment at the interface between slag and steel. The results show that the criterion number C increases with mold width, which is consistent with the results of flaw detection. Therefore, criterion number C can be used to reflect the severity of slag entrapment in different molds.

Influence of EMS on Asymmetric Flow with Different SEN Clogging Rates in a Slab Continuous Casting Mold

Submerged entry nozzle (SEN) clogging is a troublesome phenomenon in the continuous casting process that can induce the asymmetric mold flow, and thus, lowering the steel product quality. In this paper, a mathematical model coupling the electromagnetic and flow fields, was developed to investigate the influence of the SEN clogging rate on the flow field and the influence of electromagnetic stirring (EMS) on the asymmetric mold flow. Slag entrapment index Rc was introduced to quantify the possibility of slag entrapment, and symmetric index S was introduced to quantify the symmetry of the flow field. The results show that as the SEN clogging rate increased, the slag entrapment index Rc increased, while the symmetric index S decreased. EMS can greatly improve the symmetry of the flow field with SEN clogging, but it cannot remove the asymmetric phenomenon completely because the stirring intensity should be controlled below the safe level to avoid slag entrapment.

Physical Simulation of Molten Steel Homogenization and Slag Entrapment in Argon Blown Ladle

Argon stirring is one of the most widely used metallurgical methods in the secondary refining process as it is economical and easy, and also an important refining method in clean steel production. Aiming at the issue of poor homogeneity of composition and temperature of a bottom argon blowing ladle molten steel in a Chinese steel mill, a 1:5 water model for 110 t ladle was established, and the mixing time and interface slag entrainment under the different conditions of injection modes, flow rates and top slag thicknesses were investigated. The flow dynamics of argon plume in steel ladle was also discussed. The results show that, as the bottom blowing argon flow rate increases, the mixing time of ladle decreases; the depth of slag entrapment increases with the argon flow rate and slag thickness; the area of slag eyes decreases with the decrease of the argon flow rate and increase of slag thickness. The optimum argon flow rate is between 36–42 m3/h, and the double porous plugs injection mode should be adopted at this time.

Optimization on Reducing Slag Entrapment in 150 × 1270 mm Slab Continuous Casting Mold

To reduce slag entrapment in 150 × 1270 mm slab continuous casting molds at the Tang Steel Company, the effect of submerged entrance nozzle (SEN) depth and casting speed on the phenomenon was studied by computational fluid dynamics simulations. Then, the slag entrapment behavior in continuous casting molds, utilizing Large Eddy Simulation (LES) by coupling the volume of fluid (VOF) method, was also used. Finally, the effect of several common oils usually used to simulate slag in water modelling on slag entrapment was discussed and the water modelling results were used to validate the numerical simulation findings. The results showed that the optimum scheme is a submerged depth of SEN 90 mm and a casting speed of 1.6 m/min. Under optimal conditions, the maximum surface velocity is smallest (0.335 m/s) and the maximum slag entrapment ratio (0.44%) appears in the position of 0.1 m below the meniscus after 15 s. The water modelling results were in good agreement with the numerical simulation results.