Optimization of Nozzle Parameters by Investigating the Flow Behavior of Molten Steel in the Mold under a High Casting Speed

Abstract

A reasonable flow field in the continuous casting mold is beneficial to produce high quality billets, and the design of the nozzle parameters of the mold is key to regulating the flow behavior of molten steel. Through combining the numerical simulation and physical experiments and taking SEN immersion depth and inner diameter as indicators, the flow behavior of molten steel in the mold during high-speed casting of a 160 mm × 160 mm billet was investigated in detail, and the nozzle parameters were optimized. The results demonstrate that, compared with the inner diameter of the nozzle, the immersion depth has a significant influence on the impact depth of molten steel. On the premise of ensuring that the velocity distribution of molten steel on the surface of the mold is uniform and the impact range inside is appropriate, the inlet immersion depth after optimization is 100–120 mm and the inner diameter is 40 mm. The corresponding impact depth is 605–665 mm, and the maximum velocity of molten steel on the mold surface is between 0.04 and 0.045 m/s. Additionally, the results of the physical experiment and numerical simulation reveal that the optimized nozzle parameters can adapt well to the continuous casting process with a high casting speed.

1. Introduction

As the key equipment of the continuous casting machine, the mold carries out the core functions of the initial solidification of molten steel and the forming of the billet shell. In the continuous casting process, molten steel is fed into the mold through the submerged entry nozzle (SEN), which will be accompanied by forced convection of the injection flow when it moves downward [1]. A reasonable flow field in the mold is conducive to the melting of the protecting slag, the floating and removal of inclusions, and the lubrication between the mold wall and the solidified shell [2,3,4]. However, an unreasonable flow field may produce large surface flow velocity and liquid level fluctuations, causing the mold slag to be involved, resulting in entrapped slag inclusions, cracks and other surface defects of the billet, and further expansion in the secondary cooling zone, seriously affecting the billet quality [5,6].

Nowadays, the rapid development of high-speed continuous casting has considerably enhanced the production efficiency of billets and promoted the progress of the continuous casting process [7,8]. However, the increase in casting speed will also bring about great changes in the flow field in the nozzle and mold, making the billet defects such as slag inclusions and cracks appear easily [9,10,11]. Therefore, regulating the flow behavior of the fluid is crucial for producing excellent strands, especially for high-speed continuous casting.

At present, some scholars have studied the flow characteristics of molten steel in the mold through numerical simulations or physical experiments [12]. Wu et al. [13] used numerical simulation to study the forced convection behavior of molten steel in detail, and found that this behavior can significantly affect the distribution law of the mushy zone and the growth of the solidified shell. Zhang et al. [14] used the large eddy model (LES) and the Reynolds-averaged Navier–Stokes (RANS) model to further explain the essence of the turbulent flow of molten steel in the mold in principle [15,16]. Moreover, Kharicha et al. [17] aimed at the problem of the asymmetric flow of molten steel caused by partial blockage of SEN, and achieved effective regulation of the flow behavior of molten steel by applying an external magnetic field to enhance the solid shell remelting. María et al. [18] utilized physical experiments combined with numerical simulation to characterize the turbulent behavior of molten steel, and found that the variations in bath levels are highly correlated. The fluid inside the mold is distributed asymmetrically owing to the partial opening of the slide valve gate used to control the mass flow of liquid. Besides, existing research shows that it is one of the economical and efficient approaches to obtain a reasonable molten steel flow field and free surface characteristics by optimizing the SEN structural parameters of the mold [19]. Calderón-Ramos et al. [20] studied the flow behavior of molten steel in the mold by means of physical simulation and numerical simulation. The study found that the square nozzle is beneficial to promoting the symmetrical flow of molten steel and reducing horizontal oscillation. Li et al. [21] observed the flow law of molten steel and found that the local velocity of the fluid, the deviation distance of the SEN, and the casting speed all have significant effects on the generation of eddy currents in the fluid. Similarly, Gupta et al. [22,23] focused on the study of the fluid fluctuation at the meniscus under different SEN parameters and the symmetry of the fluid in the mold, and interpreted the bubble entrainment phenomenon. In addition, Zhang et al. [24] found that the geometry of the SEN has a significant effect on the flow law of molten steel, and observed three fluid flow patterns in the SEN. Among them, the annular flow structure will cause asymmetric flow and even horizontal fluctuation in the mold, which is not conducive to the floating of gas and inclusions.

In the past, most of the research on the physical experiment and numerical simulation of the continuous casting process adopted the conventional casting speed (≤3.0 m/min), and there were few reports about the flow behavior of molten steel and the optimization of SEN structural parameters under high casting speed, lacking reliable optimization solutions. In fact, the design and optimization of the nozzle parameters of the continuous casting mold is vital for high-speed continuous casting. The impact depth of the molten steel infused into the mold has a great relationship with the SEN immersion depth. In addition, the selection of the inner diameter of the SEN nozzle is also critical for the smooth injection of molten steel. Accordingly, it is necessary to study the nozzle parameters suitable for a high casting speed, and to clarify its influence on the flow field, so as to control the fluctuation of the molten steel level in the mold, facilitate the floating of inclusions, and promote the uniform growth of the solidified shell of the billet.

In view of the shortcomings of previous studies, this study firstly explored the influence of nozzle parameters (nozzle size and SEN immersion depth) on the flow field distribution and liquid level fluctuation in the mold by numerical simulation, and clarified the distribution characteristics of molten steel. Secondly, the characteristics of the flow field and the distribution of liquid slag under different casting speeds were studied by means of physical simulation, and the results were compared and verified with the numerical simulation results, optimizing the parameters of the SEN in the mold. In addition, on the basis of the above research, the flow behavior of molten steel in the mold and its effect on continuous casting and billet quality under different casting speeds were also evaluated. The research results can provide some valuable information for the development of billet high-speed continuous casting technology and the optimization of SEN parameters.

2. Mathematical Model

2.1. Governing Equations

The molten steel in the mold is regarded as a continuous three-dimensional steady state incompressible fluid, and the specific continuity equation and N–S equation are shown as Equations (1)–(6). Among them, for the momentum equation, the standard k-ε double equations in the Reynolds-averaged N–S equations model are used to solve the following:

$$\mathrm{Continuity} \mathrm{Equation}: \nabla \cdot \overrightarrow{v}=0$$

(1)

where $\overrightarrow{v}$ is the velocity vector, m/s.

$$\mathrm{N}–\mathrm{S} \mathrm{Equation}: \rho \frac{\partial \overrightarrow{v}}{\partial t}+\rho \nabla \cdot (\overrightarrow{v}\overrightarrow{v})=-\nabla P+\nabla \cdot (\overrightarrow{\overline{\tau }})+\rho \overrightarrow{g}+\overrightarrow{F}$$

(2)

where $\rho$ is the fluid density, kg/m³; P is the hydrodynamic pressure, Pa; $\rho \overrightarrow{g}$ and $\overrightarrow{F}$ are the gravitational body force and the external body force, respectively; and $\overrightarrow{\overline{\tau }}$ is the viscous stress tensor generated on the surface of the control body owing to the viscous effect of molecules.

$$\overrightarrow{\overline{\tau }}=\mu \left[(\nabla \cdot \overrightarrow{v}+\nabla \cdot {\overrightarrow{v}}^T)-\frac{2}{3}\nabla \overrightarrow{v}I\right]$$

(3)

In the formula, $\mu$ is the molecular viscosity of the fluid, kg/(m·s), and I is the unit tensor.

Standard k-ε double equations:

$$\frac{\partial }{\partial t}(\rho k)+\frac{\partial }{\partial x_i}\left(\rho k{v}_i\right)=\frac{\partial }{\partial x_j}\left[\left(\mu +\frac{{\mu }_t}{{\sigma }_k}\right)\frac{\partial k}{\partial x_j}\right]+G_k+G_b-\rho \epsilon -Y_M$$

(4)

$$\frac{\partial }{\partial t}(\rho \epsilon )+\frac{\partial }{\partial x_i}\left(\rho \epsilon v_i\right)=\frac{\partial }{\partial x_j}\left[\left(\mu +\frac{{\mu }_t}{{\sigma }_{\epsilon }}\right)\frac{\partial \epsilon }{\partial x_j}\right]+C_{1\epsilon }\frac{\epsilon }{k}\left(G_k+C_{3\epsilon }{G}_b\right)-C_{2\epsilon }\rho \frac{{\epsilon }^2}{k}$$

(5)

where G_k is the turbulent kinetic energy generation term owing to the average velocity gradient; G_b is the turbulent kinetic energy generation term owing to buoyancy; Y_M is the contribution of pulsating expansion to the total dissipation rate in compressible turbulent flow and, for incompressible fluids, its value is zero; $C_{1\epsilon }$, $C_{2\epsilon }$, and $C_{3\epsilon }$ are constants; and ${\sigma }_k$ and ${\sigma }_{\epsilon }$ are the turbulent Prandtl numbers of k and ε, respectively. ${\mu }_t$ is the turbulent viscosity, which can be solved jointly by k and ε:

$${\mu }_t=\rho C_{\mu }\frac{k^2}{\epsilon }$$

(6)

where $C_{\mu }$ is a constant. This study takes $C_{1\epsilon }$ = 1.44, $C_{2\epsilon }$ = 1.92, $C_{3\epsilon }$ = $C_{\mu }$ = 0.09, ${\sigma }_k$ = 1.00, and ${\sigma }_{\epsilon }$ = 1.30.

At the same time, the calculation takes into account the heat transfers between the mold and the molten steel. Energy conservation equation:

$$\frac{\partial }{\partial t}(\rho H)+\nabla \cdot (\overrightarrow{v}(\rho H+P))=\nabla \cdot (k_{eff}\nabla T)$$

(7)

In the formula, H is the enthalpy, J/kg; $k_{eff}$ is the effective thermal conductivity, W/(m·K); and P is the pressure, Pa. In addition, H can be obtained by Equation (8):

$$H=h_{ref}+{\displaystyle {\int }_{T_{ref}}^T{C}_p}dT+\beta L$$

(8)

where $h_{ref}$ is the reference enthalpy, J/kg; $T_{ref}$ is the reference temperature, K; $C_p$ is the specific heat, J/(kg·K); $\beta$ is the liquid phase ratio; and L is the latent heat of solidification, J/kg.

The liquidus rate $\beta$ can be determined by both the solidus and the liquidus temperature.

$$\beta =\left\{\begin{array}{ll}0\hfill & T<T_{solidus }\hfill \\ \frac{T-T_{solidus}}{T_{liquidus}-T_{solidus}}\hfill & T_{solidus}<T<T_{liquidus}\hfill \\ 1\hfill & T>T_{liquidus}\hfill \end{array}\right.$$

(9)

where $T_{liquidus}$ and $T_{solidus}$ are the liquidus and solidus temperatures, respectively.

2.2. Model Description

According to the flow of molten steel in the mold based on the symmetry of the nozzle center plane parallel to the side arc, the calculation area is taken as half of the mold. The research object is the arc-shaped mold. Fluent14.0 commercial software (Ansys, Canonburg, PA, USA) is utilized to solve the heat transfer behavior of fluid flow in the model. The solution method adopts SIMPLE and uses the transient calculation method [25,26]. The time step is selected as 0.01 s, a total of 4000 steps. At the entrance of the SEN, the velocity-entry boundary condition is used. According to the casting speed and the law of conservation of mass, the initial speed of the mold inlet is calculated. In addition, the inlet value of turbulent kinetic energy and turbulent energy dissipation rate are 0.00001, respectively. The pressure outlet boundary condition is adopted at the outlet of the mold. The top free surface was set as zero shear stationary wall and heat insulation. On the symmetry plane of the model, assume that the normal velocity component and normal gradient of all other variables are 0. At the surface of billet, the heat transfer boundary condition was employed for the heat flux, which decreased along the casting direction. The main simulation parameters of the billet mold are listed in

Table 1. The main parameters of the casting mold.

Operating Parameters	Values
Mold section/(mm × mm)	160 × 160
Mold length/mm	1000
SEN type	Straight through
Casting speed/(m·min−1)	3.0, 3.5, 4.0, 4.5
insertion depth of SEN/mm	80, 100, 120, 140, 160
Inner diameter of SEN/mm	30, 35, 40, 45
Steel viscosity/(Pa·s)	0.0065
Steel density/(kg·m−3)	7200
Liquidus temperature of steel/K	1793
Solidus temperature of steel/K	1748
Steel latent heat/(kJ/kg)	264
Steel heat capacity/(J/kg·K)	720

. It is noted that, in the simulation process, we control the casting speed by adjusting the amount of water injected into the mold per unit time. The immersion depth is determined by adjusting the distance that the nozzle is inserted into the mold. In addition, the nozzle size is adjusted by establishing different mathematical models. Moreover, we have made appropriate assumptions in the calculation process. (1) The molten steel is regarded as an incompressible fluid; (2) the influence of a small amount of chemical reactions existing in the mold is ignored, and the molten steel is regarded as a homogeneous medium; (3) the free liquid level of the crystallizer is horizontally stable; and (4) the vibration of the mold is not considered. In order to ensure the reliability of the calculation results, the length of the calculation area is slightly larger than the real length of the mold. The whole model is divided into hexahedral elements. The skewness and orthogonality of the meshes are 0.2–0.65 and 0.4–0.8, respectively, and the total number of meshes is 400,000. The implementation of the boundary conditions of the mold model and the schematic diagram of mesh division are shown in Figure 1.

3. Results and Discussion

3.1. Optimization of the Insertion Depth of SEN

The immersion depth of SEN in the mold will affect the impact depth and flow state of the molten steel, which will have a significant impact on the formation of the solidified shell and the floating of inclusions. Figure 2 and Figure 3 show the velocity field of the impact depth of molten steel entering the mold under different casting speeds (3 m/min–4.5 m/min) and the relationship between the impact depth and the SEN immersion depth. It can be seen that the high-speed areas of the molten steel are located in the SEN and at the outlet of the SEN, and gradually decrease as the molten steel flows vertically downward; finally, the velocity decreases to the lowest at the wall surface of the billet. In addition, it can be clearly seen from Figure 3 that the immersion depth of the nozzle has a significant effect on the impact depth of the molten steel in the mold, and the impact depth of the molten steel increases rapidly with the increase in the immersion depth at each casting speed.

The deeper the immersion depth of SEN, the greater the impact depth of molten steel, which is harmful to the floating of inclusions, and in turn adversely affects the quality of the billet. This is mainly because of the increase in the immersion depth and the increase in the hydrostatic pressure of the molten steel in the mold, and the relative impact depth of the impinging stream relative to the outlet of the nozzle decreases. The scope of the outer arc recirculation zone becomes smaller and the scope of the inner arc recirculation zone becomes larger, the center of the recirculation zone moves down, but the kinetic energy of the recirculation strand is weakened, which has a negative impact on the floating of inclusions. However, the immersion depth of the SEN should not be too shallow, which will cause the molten steel to fluctuate greatly on the liquid level in the mold, which will affect the uniformity of the distribution of the mold slag layer. Therefore, for a high casting speed, when the immersion depth of the nozzle is 160 mm, the impact depth of the stream and the position of the recirculation zone are too deep, which is adverse to the floating of inclusions. On the contrary, when the immersion depth of the nozzle is 80 mm, it is too shallow, and the return flow disturbs the liquid level of the mold greatly, which is not conducive to the uniform distribution of the slag layer on the liquid level.

Additionally, the distribution of the molten steel flow rate on the mold surface affects the activity and uniformity of the liquid slag distribution, which is crucial for the production of high-quality billets. Figure 4 shows the velocity field of the molten steel on the surface of the mold, from which the distribution information of the surface molten steel flow rate and the maximum flow rate can be obtained intuitively. The maximum flow rate of molten steel on the surface under different immersion depths is shown in Figure 5. It can be seen that the maximum speed of the liquid surface is between 0.04 and 0.055 m/s at varying immersion depths at a high casting speed. The influence of water inlet immersion depth at varying casting speeds on the molten steel flow rate on the mold liquid surface is complex, and the velocity distribution of molten steel is slightly different. In general, however, the steel level is relatively active under all working conditions, which is conducive to the melting of protective slag. However, the flow rate of molten steel on the surface should not be too large, otherwise it will easily cause uneven distribution of liquid slag, which will lead to the risk of slag entrapment. Consequently, considering reducing the fluctuation of the liquid level, ensuring that the liquid surface velocity and velocity gradient are gentle and uniformly distributed, the immersion depth of the high-speed immersion nozzle should be selected to be about 120 mm, and the corresponding maximum liquid surface velocity of the mold is 0.04–0.045 m/s.

Generally speaking, the appropriate immersion depth of the immersion nozzle at each casting speed in actual production is not a fixed value, but is within a certain range. In addition, under the condition of meeting the requirements of each casting speed at the same time, the immersion depth of the same set of immersion nozzles should be ensured as much as possible, so as to improve the production efficiency. Therefore, based on the comprehensive analysis of the influence of varying immersion depths on the flow field distribution in the mold and the maximum flow rate of the liquid surface, the suitable immersion depth of the immersion nozzle in the range of high casting speed is 100–120 mm.

3.2. Optimization of SEN Inner Diameter

With the increase in the continuous casting speed, the amount of steel passing through also increases. A suitable SEN inner diameter is an important condition to ensure that the molten steel can enter the mold smoothly under a high casting speed. Figure 6 shows the relationship between the impact depth of the molten steel and the inner diameter of the SEN at different casting speeds when the SEN immersion depth is 120 mm. It can be obtained that, compared with the insertion depth of SEN, the influence of nozzle size on the impact depth of molten steel is not obvious. With the increase in the inner diameter of the nozzle, the fluctuation of the impact depth is smooth, and there is no obvious rule. Under the same casting speed, the difference of impact depth is in the range of 5–30 mm. Therefore, based on the above research results, we believe that the immersion depth of the SEN has a greater influence on the flow behavior of molten steel than the inner diameter of the nozzle.

Figure 7 presents the relationship of maximum flow speed on the surface in the mold and SEN inner diameter. The maximum flow speed of molten steel at different nozzle diameters under various casting speeds is between 0.03 and 0.05 m/s, which can maintain a certain activity. In addition, when the inner diameter is 30 mm and 45 mm, if the casting speed changes, the flow rate of molten steel will fluctuate greatly, which will easily lead to uneven distribution of the liquid slag layer. On the contrary, when the inner diameter is 50 mm and 40 mm, the maximum velocity distribution on the surface of mold is relatively stable at each casting speed, which is conducive to stabilizing the flow state of the molten steel when the casting speed changes and reducing the probability of mold slag being involved. However, when the flow rate of the liquid surface of the mold is too large, it is easy to cause uneven liquid level or even slag entrainment, and when the flow rate is small, the liquid level is too calm and slagging is caused easily, which is not conducive to continuous casting. Consequently, in order to reduce the fluctuation of molten steel on the surface of the mold and maintain its active state, and considering the stability of molten steel on the surface when the casting speed changes, the appropriate inner diameter of the nozzle should be 40 mm.

3.3. Influence of Casting Speed on Flow Behavior of Molten Steel

On the basis of obtaining the appropriate SEN immersion depth and inner diameter, we further studied the effect of casting speeds on the flow behavior of molten steel in the mold. Figure 8 and Figure 9 present the velocity field and trajectory diagram of the flow field under distinct casting speeds when the SEN immersion depth is 120 mm and the SEN inner diameter is 40 mm, respectively. It can be clearly seen that, the greater the casting speed, the deeper the impact depth of the molten steel in the mold, but the numerical difference is small. The impact depths of molten steel at four casting speeds of 3.0 m/min, 3.5 m/min, 4.0 m/min, and 4.5 m/min are 625 mm, 635 mm, 650 mm, and 665 mm, respectively. Compared with the flow form of the molten steel, the increase in the casting speed has a greater impact on the flow strength of the molten steel.

Furthermore, the flow of molten steel forms upper and lower reflux zones in the mold. With the increase in the casting speed, the higher the inlet velocity of the molten steel, the larger the turbulent kinetic energy, resulting in a larger impact depth, so the inner and outer arc recirculation zones gradually move down. When the impact depth is too large, the energy required for inclusions and bubbles to float up is greater, which makes it more difficult to remove. Nevertheless, enhancing the casting speed properly can promote the active flow of molten steel, reduce the flow dead zone, and make the heat distribution of molten steel at the meniscus more uniform, thereby increasing the uniformity of the billet shell and improving the surface quality of the billet.

Figure 10 shows the flow velocity distribution of molten steel on the mold surface under different casting speeds. With the increase in the casting speed, the flow rate and flow gradient increase, and the high-speed area also increases, but the overall difference is small. The corresponding maximum speed is controlled at 0.04–0.045 m/s. Although the maximum flow rate under the working condition of 3.5 m/min is greater than that of 4 m/min and 4.5 m/min, the area where the flow velocity is greater than 0.03 m/s is much smaller than the other two working conditions. This is primarily because of the increase in the casting speed and the increase in the kinetic energy of the main stream flowing out of the nozzle, which results in a significant increase in the scope and kinetic energy of the recirculation zone, and makes the liquid level fluctuate violently, which easily leads to a large local molten steel flow rate. In general, however, the flow velocity of molten steel on the mold surface is uniform and active in the casting speed range of 3.0–4.5 m/min, which is favorable for the uniform distribution and melting of the slag layer.

3.4. Verification of Numerical Simulation Results

3.4.1. Flow Field in the Mold

In order to obtain the flow state of the molten steel in the mold and the fluctuation of the molten steel on the surface more intuitively and clearly, as well as at the same time to verify the accuracy of the numerical simulation results, the physical experiment method was utilized to select a nozzle parameter with an inner diameter of 40 mm and an immersion depth of 120 mm, investigating the flow law of molten steel and the distribution of molten steel slag on the surface under different casting speeds. The details and parameters of physical experiments have been described in detail in our previous research [27]. The materials of mold are polymethyl methacrylate (PMMA). Additionally, the results of the mold flow field obtained from numerical simulation and physical experiment at a high casting speed were compared, as shown in Figure 11.

It can be found that the flow field law obtained by numerical simulation and physical experiment is similar, and the impact range of the stream is roughly the same.

Table 2. Comparison of the impact depth under different casting speeds.

Project	Impact Depth, mm
	3.0 m/min	3.5 m/min	4.0 m/min	4.5 m/min
Numerical simulation	625	635	650	665
Physic experiment	550	563	575	579
Difference	75	72	75	86
Error/%	12.0	11.3	11.5	12.9

summarizes the impact depth of molten steel at different casting speeds under the two research methods. It can be seen that the impact depth of the mold stream increases with the increase in the casting speed. Among them, the impact depth of the numerical simulation stream is about 620–665 mm, while of the physical experiment stream is about 550–580 mm. The difference between the two is about 70–85 mm, and the overall error is between 11% and 13%. Because of the limitations of numerical simulation methods, we have to adopt some assumptions to simplify the solution process on the premise of ensuring the accuracy as much as possible. This will also cause the numerical simulation results to deviate from reality. Although there are certain differences in the impact depth results obtained by the two, the overall trend is the same, which can be compared and verified. Therefore, the distribution of the flow field inside the mold is reasonable under different working conditions obtained by numerical simulation.

3.4.2. Liquid Slag Distribution

The flow field distribution of molten steel on the mold surface has a critical influence on the distribution of liquid slag, and it affects the surface quality of the billet to a certain extent. Based on the established water modeling device, the distribution of liquid slag on the surface of the continuous casting mold was studied at a high casting speed of 3.0~4.5 m/min. The results of the liquid flow field are shown in Figure 12. According to the fluidity of the liquid slag on the mold surface and the exposure state of the molten steel, the distribution uniformity of the liquid slag is divided into several grades. The specific classification standards have been elaborated in our previous research [27]. It can be seen from the research results that the liquid slag distribution is uniform under all working conditions, and there is no molten steel exposure and slag entrainment phenomenon, indicating that the optimized nozzle parameters can be well adapted to a 3.0~4.5 m/min continuous casting production process.

4. Conclusions

We present the detailed investigation of the flow behavior of molten steel in the mold during high-speed continuous casting by numerical simulations and physical experiments. On this basis, the SEN parameters of the mold were optimized. Moreover, the fluctuation of molten steel and the distribution of molten slag on the surface of the mold were also analyzed and evaluated. The specific conclusions are classified as follows:

(1)

The high-speed zone of molten steel flow in the mold is located in the SEN and at the outlet of the SEN, and progressively decreases with the vertical downward flow of the molten steel; eventually, the velocity decreases to the minimum at the wall surface of the billet. In addition, the impact depth of molten steel increases swiftly with the increase in SEN immersion depth, while the difference in impact depth under different sizes of nozzle inner diameter is slight, all in the range of 5–30 mm. Compared with the inner diameter of SEN, the immersion depth of SEN has a greater impact on the impact depth of molten steel.

(2)

In order to guarantee the uniform distribution of molten steel flow velocity on the mold surface and the proper impact depth, within the casting speed range of 3.0~4.5 m/min, the optimized SEN immersion depth is 100~120 mm, and the SEN inner diameter is 40 mm. The impact depth of the corresponding stream is 605–665 mm, and the maximum flow rate of molten steel on the mold surface is between 0.04 m/s and 0.045 m/s.

(3)

With the increase in the casting speed, the impact depth of molten steel in the mold increases slightly. In addition, the molten steel flow rate and gradient on the mold surface increased, and the area of the high-speed region also increased moderately. In general, the flow rate on the mold surface is uniform and active in the casting speed range of 3.0–4.5 m/min, which is beneficial to the uniform distribution and melting of the slag layer.

(4)

The distribution law of the flow field in the mold obtained by the physical experiment and the numerical simulation is identical, and the impact range of the flow strand is approximately the same. In addition, the distribution of the slag layer on the surface of the mold is uniform, which guarantees the activity of the liquid slag without the exposure of molten steel and the entrainment of slag. The research results illustrate that the optimized SEN parameters can be well adapted to the production of the continuous casting process when the casting speed is 3.0–4.5 m/min.