Component prediction and length calculation method for dissimilar steel continuous casting and mixed casting blank

Abstract

The invention discloses a component prediction and length calculation method for a dissimilar steel continuous casting and mixed casting blank. The method comprises the steps that a tundish multiphase flow mathematical model and a casting blank solidification and mass transfer coupling model are established and verified; the different steel grade continuous casting process under different technological parameter combinations is simulated, new steel grade concentration change data at a tundish outlet are obtained, and the influence of the technological parameters on the mixed casting behavior in the tundish is analyzed; analyzing the influence of key process parameters on molten steel exposure, slag layer distribution and slag entrapment risk in a flow injection area in the liquid level descending and liquid level ascending processes; the concentration change data of the new steel grade at the outlet of the tundish is used as an input boundary condition of the casting blank solidification and mass transfer coupling model, distribution of key elements in the mixed casting blank is simulated and predicted, and the length of the mixed casting blank is calculated; and the optimal process control parameters with the aim of shortening the length of the mixed casting blank are determined by integrating the length of the mixed casting blank and the molten steel cleanliness risk analysis result. The method has the advantages of accurately predicting component distribution and length of the mixed casting blank, optimizing process control parameters and the like.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology in iron and steel metallurgy, specifically to a method for predicting the composition and calculating the length of mixed-cast billets made from dissimilar steels. Background Technology

[0002] In steel production, continuous casting of dissimilar steels is widely used to improve production efficiency and reduce production costs. However, during continuous casting of dissimilar steels, due to the alternation of old and new steel grades, mixed casting zones can form in the tundish, crystallizer, and liquid phase cavity, resulting in mixed-cast billets. Mixed-cast billets refer to the billets cast at the interface between old and new steel grades, whose chemical composition does not meet the standard requirements of either steel grade. They usually need to be downgraded or scrapped, resulting in resource waste and increased production costs.

[0003] Currently, steel companies mainly rely on experience to control the continuous casting process of dissimilar steels, lacking accurate methods for predicting the composition distribution and length of mixed-cast billets. In actual production, operators typically set process parameters such as the amount of steel remaining in the tundish, continuous casting speed, and the filling flow rate of new steel grades based on historical data and field experience. However, due to the complexity of molten steel flow, mass transfer, and interfacial behavior within the tundish, as well as the transport characteristics of key elements during billet solidification, it is difficult to accurately predict the composition distribution and length of mixed-cast billets based solely on experience.

[0004] As a key piece of equipment in the continuous casting process, the tundish's internal flow field significantly impacts the mixing process. During the continuous casting of dissimilar steels, complex multiphase flow and mass transfer phenomena occur between the molten steel, covering agent, and air within the tundish. Particularly during the lowering and raising of the liquid level, fluctuations in the molten steel surface can lead to exposed molten steel in the pouring zone, uneven slag distribution, and an increased risk of slag entrapment, thus affecting the cleanliness of the molten steel. Furthermore, the transport behavior of key elements during the solidification process of the billet also influences the compositional distribution of the mixed-cast billet.

[0005] While some studies in the field have analyzed the continuous casting process of dissimilar steels through physical and numerical simulations, these methods often focus only on a single stage, such as the tundish or the billet, lacking a systematic study of the entire continuous casting process. Furthermore, existing models typically fail to accurately reflect the complex operating conditions in actual production, such as dynamically changing process parameters and multiphase interface behavior, leading to significant discrepancies between predicted results and actual conditions.

[0006] In terms of process parameter optimization, existing technologies mainly rely on trial and error to determine the optimal process conditions. This is not only time-consuming and labor-intensive, but also makes it difficult to fully consider the interactions between various process parameters. For example, reducing the amount of residual steel in the tundish can shorten the length of the mixed billet, but too low a residual steel amount may lead to an excessively low molten steel level, causing vortex slag entrainment problems. Increasing the ladle flow rate can accelerate the mixing of new and old steel grades, but an excessively high flow rate will exacerbate the exposure of molten steel, increasing the risk of secondary oxidation. Therefore, determining the optimal process control parameters while ensuring the cleanliness of molten steel is a significant challenge currently facing the technology.

[0007] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0008] In view of this, the present invention provides a method for predicting the composition and calculating the length of mixed-cast billets of dissimilar steels, which has the advantages of accurately predicting the composition distribution and length of mixed-cast billets, optimizing process control parameters, reducing resource waste and production costs, and improving production efficiency.

[0009] This invention proposes a method for predicting the composition and calculating the length of dissimilar steel continuously cast billets, comprising: S1. Establish a mathematical model of multiphase flow in the tundish to simulate the flow, mass transfer, and interfacial behavior of molten steel, covering agent, and air during the continuous casting of different steel grades. S2. Establish a billet solidification and mass transfer coupling model to simulate the billet flow, solidification, heat transfer and transport of key alloying elements during continuous casting. S3. The mathematical model of multiphase flow in the tundish and the coupling model of solidification and mass transfer of the billet are verified by physical simulation and industrial test data. S4. Based on the verified mathematical model of multiphase flow in the tundish, simulate the continuous casting process of different steel grades under different combinations of process parameters, obtain the concentration change data of new steel grades at the tundish outlet, and analyze the influence of process parameters on the mixing behavior in the tundish. S5. Based on the multiphase flow simulation results of the tundish multiphase flow mathematical model, analyze the impact of key process parameters on the exposure of molten steel in the injection zone, slag layer distribution and slag entrapment risk during the liquid level drop and liquid level rise processes. S6. Use the concentration change data of the new steel grade at the outlet of the tundish as the input boundary condition of the solidification and mass transfer coupling model of the billet, simulate and predict the distribution of key elements in the mixed billet, and calculate the length of the mixed billet. S7. Based on the combined analysis results of the risk assessment of the length of the mixed billet and the cleanliness of the molten steel, determine the optimal process control parameters with the goal of shortening the length of the mixed billet.

[0010] As can be seen from the above, the method for predicting the composition and length of mixed-cast billets of dissimilar steel provided in this application, by establishing a mathematical model of multiphase flow in the tundish and a coupled model of solidification and mass transfer of the billet, simulates different combinations of process parameters, predicts the composition distribution and length of the mixed-cast billets, and determines the optimal control parameters, thereby accurately predicting the composition distribution and length of the mixed-cast billets and optimizing process control. It has the advantages of improving prediction accuracy, reducing resource waste and production costs, and improving production efficiency. Attached Figure Description

[0011] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0012] Figure 1 This is a flowchart illustrating a method for predicting the composition and calculating the length of a mixed-cast billet made of dissimilar steels according to an embodiment of the present invention. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] like Figure 1 As shown, this application provides a method for predicting the composition and calculating the length of dissimilar steel continuously cast billets, the specific implementation of which may include the following steps: First, a mathematical model of multiphase flow in the tundish is established. This model is used to simulate the flow, mass transfer, and interfacial behavior of molten steel, covering agent, and air during the continuous casting of different steel grades.

[0015] Specifically, the mathematical model of multiphase flow in the tundish is used to describe the complex flow, mass transfer, and interfacial interactions of molten steel, covering agent, and air within the tundish during continuous casting of different steel grades. This model allows for the quantitative analysis of the steel mixing process and flow field characteristics within the tundish.

[0016] Secondly, a coupled model of billet solidification and mass transfer was established. This model is used to simulate the flow, solidification, heat transfer, and transport of key elements in the billet during continuous casting.

[0017] Specifically, the billet solidification and mass transfer coupling model is used to simulate the flow of molten steel, solidification process, heat transfer, and transport behavior of key elements inside the billet during continuous casting. This model can predict the composition distribution of the billet during solidification, providing a basis for calculating the length of the mixed-cast billet.

[0018] Next, physical simulations and industrial test data were used to verify the mathematical model of multiphase flow in the tundish and the coupling model of solidification and mass transfer in the billet. Physical simulations refer to establishing a scaled-down model with similar criteria to the actual production process, such as a water model, and using tracers and other methods to simulate and measure the fluid behavior within the tundish under laboratory conditions to obtain experimental data. Industrial test data refers to data obtained in actual steel production sites through continuous casting tests of different steel grades, involving real-time monitoring and sampling analysis of key parameters and product quality during the production process.

[0019] Then, based on the validated mathematical model of multiphase flow in the tundish, the continuous casting process of different steel grades under different combinations of process parameters was simulated to obtain data on the concentration change of the new steel grade at the tundish outlet, and the influence of process parameters on the mixing behavior in the tundish was analyzed. For example, only the single tundish residual steel amount or continuous casting speed condition can be simulated to observe its influence on the mixing area of ​​new and old steel grades; or, the diffusion rate of the new steel grade under different parameters can be qualitatively determined simply by visualizing the flow field cloud map.

[0020] Furthermore, based on the simulation results of the tundish multiphase flow mathematical model, the impact of key process parameters during the lowering and raising of the liquid level on the exposure of molten steel, slag layer distribution, and slag entrapment risk in the pouring zone is analyzed. For example, the presence of exposed molten steel or slag layer fluctuations can be determined simply by observing the simulation animation; or, based on experience, slag entrapment may occur at a specific liquid level without performing a detailed vortex formation simulation. The process parameter combination refers to the specific combination of various controllable parameters affecting the flow, mixing, solidification, and cleanliness of molten steel during continuous casting of different steel grades, such as the remaining steel quantity in the tundish, continuous casting speed, and the filling flow rate of the new steel grade.

[0021] Subsequently, the data on the concentration variation of the new steel grade at the tundish outlet is used as the input boundary condition for the billet solidification and mass transfer coupling model to simulate and predict the distribution of key elements in the mixed billet and calculate the length of the mixed billet. For example, the average concentration of the new steel grade at the tundish outlet can be used as a constant input to the billet model without considering its dynamic changes; or, a fixed time period can be set as the length of the mixed billet without being based on specific element concentration criteria. The length of the mixed billet refers to the actual length of the billet segment formed by the mixing of new and old steel grades during the continuous casting of dissimilar steels, where the content of key elements does not meet the respective internal control standards of the new and old steel grades.

[0022] Finally, based on the combined analysis of the mixed-cast billet length and steel cleanliness risk, the optimal process control parameters with the goal of shortening the mixed-cast billet length were determined. For example, parameters could be selected solely based on minimizing the mixed-cast billet length, without fully considering the steel cleanliness risk; alternatively, a trial-and-error approach could be used to select a relatively optimal solution from a limited set of parameter combinations. Steel cleanliness risk refers to the potential risk that, during the continuous casting of dissimilar steels, factors such as exposed molten steel, slag entrapment, and secondary oxidation can lead to an increase in non-metallic inclusions in the molten steel, thereby affecting the billet quality. Optimal process control parameters refer to the process parameter settings that, through comprehensive analysis of the mixed-cast billet length and steel cleanliness risk, achieve the shortest mixed-cast billet length while keeping the steel cleanliness risk controllable, while meeting production requirements and quality standards.

[0023] This method establishes and validates a coupled model of multiphase flow in the tundish and solidification mass transfer in the billet, enabling a systematic simulation of the entire process of continuous casting of dissimilar steels. This allows for accurate prediction of the composition distribution and length of the mixed-cast billets. Through comprehensive analysis of process parameters, this method can effectively optimize control strategies, achieving the goal of shortening the length of the mixed-cast billets while significantly reducing the risk to molten steel cleanliness and improving production efficiency and product quality.

[0024] This application further proposes the governing equations of the tundish multiphase flow mathematical model, including the continuity equation, momentum conservation equation, turbulence model equation, component transport equation, and VOF multiphase flow equation; in the boundary conditions of the tundish multiphase flow mathematical model, the inlet boundary adopts the mass flow rate that changes dynamically according to the continuous casting stage, and the outlet boundary adopts the mass flow rate that changes according to the casting speed.

[0025] Specifically, in the governing equations of the multiphase flow mathematical model in the tundish, the continuity equation describes the conservation of fluid mass, ensuring that the inflow, outflow, and internal changes of the fluid within the tundish conform to the law of conservation of mass during the simulation. This can be achieved by mathematically expressing the divergence of the fluid density and velocity fields; for example, the divergence is zero for incompressible fluids, while for compressible fluids, the density change over time must be considered. The momentum conservation equation describes the relationship between the forces acting on the fluid during its motion and the change in fluid momentum, thus accurately capturing the flow behavior of molten steel within the tundish. This can be achieved using the Navier-Stokes equations, which consider the influence of inertial forces, pressure gradient forces, viscous forces, and external body forces on fluid motion. The turbulence model equations describe the characteristics of turbulent fluid motion. By introducing a turbulence model, the complex flow state of molten steel within the tundish can be simulated more accurately. Common implementation methods include... Model, Models such as the Reynolds stress model, or similar models, describe turbulent characteristics such as turbulent kinetic energy and turbulent dissipation rate by introducing additional transport equations. Component transport equations describe the transport and mixing processes of different components within the tundish and are key to distinguishing the mixing behavior of new and old steel grades. This can be achieved by solving partial differential equations relating component concentrations to time and space, considering both convection and diffusion transport mechanisms. The VOF multiphase flow equation describes the interfacial behavior between three immiscible fluids—molten steel, covering agent, and air—within the tundish, accurately capturing the distribution and interactions of multiphase fluids. This can be achieved using the volume fraction method, which determines phase interfaces by tracking the volume fraction of each phase, thereby simulating complex phenomena such as interface deformation, breakage, and merging.

[0026] In the boundary conditions of the mathematical model for multiphase flow in the tundish, the inlet boundary uses a mass flow rate that dynamically changes according to the continuous casting stage. This simulates the actual change in molten steel flow rate at the tundish inlet during the continuous casting process (such as steady casting, lowering the liquid level, and raising the liquid level during filling), ensuring the model reflects the real working conditions of the production site. This can be achieved through a preset flow-time curve or by adjusting the inlet flow rate in real time according to changes in the tundish liquid level. For example, the inlet mass flow rate can be set to zero during the lowering liquid level stage, a relatively large constant flow rate during the raising liquid level filling stage, and equal to the total outlet flow rate during the steady casting stage. The outlet boundary uses a mass flow rate that changes according to the casting speed, simulating the change in molten steel flow rate at the tundish outlet with the continuous casting machine speed. This ensures the model remains consistent with the actual production rhythm of the downstream continuous casting process. This can be achieved by establishing a functional relationship between the outlet mass flow rate and the continuous casting speed. For example, based on the billet cross-sectional dimensions and molten steel density, the casting speed can be converted into a corresponding mass flow rate, and the outlet flow rate can be updated in real time according to the dynamic adjustment of the casting speed.

[0027] Through the above technical solutions, this application can significantly improve the simulation accuracy and realism of the tundish multiphase flow mathematical model for the continuous casting process of different steel grades. Specifically, the continuity equation ensures the accurate conservation of fluid mass, avoiding spurious mass increases or decreases during the simulation process; the momentum conservation equation can accurately capture the complex flow patterns of molten steel in the tundish, including turbulence and backflow, providing a solid flow field foundation for subsequent mass transfer and interface behavior analysis; the turbulence model equation further refines the description of turbulence effects, making the model more reliable when dealing with high Reynolds number flows; the component transport equation directly quantifies the mixing degree and distribution of new and old steel grades, providing core data for predicting the composition of mixed-cast billets; and the VOF multiphase flow equation can finely simulate the interface dynamics between molten steel, covering agent, and air, such as slag layer distribution, exposed molten steel, and potential slag entrapment risk, which is crucial for assessing the cleanliness of molten steel. Meanwhile, the dynamically changing inlet mass flow boundary conditions enable the model to faithfully reflect the flow changes during key stages of actual production, such as ladle replacement and liquid level fluctuations, avoiding errors caused by static boundary conditions. The outlet mass flow boundary conditions, based on changes in casting speed, ensure seamless integration between the tundish model and the downstream continuous casting process, making the simulation of the entire continuous casting process more coherent and accurate. The synergistic effect of these governing equations and boundary conditions allows the tundish multiphase flow mathematical model to accurately reproduce the flow, mass transfer, and interfacial behavior of molten steel, covering agent, and air during the continuous casting of different steel grades. This provides more reliable and accurate basic data for subsequent simulations of process parameter combinations, analysis of mixed casting behavior, prediction of key element distribution, and calculation of mixed casting billet length based on this model. Ultimately, this enables more effective determination of optimal process control parameters to shorten the mixed casting billet length and reduce the risk of molten steel cleanliness issues.

[0028] In one optional implementation, the dynamically changing mass flow rate is set as follows: during the stable casting stage, the inlet mass flow rate is equal to the sum of all outlet mass flow rates; during the liquid level lowering stage, the inlet mass flow rate is zero; during the liquid level raising filling stage, the inlet mass flow rate is set to a constant first flow rate value greater than the stable casting flow rate; and after the liquid level stabilizes, the inlet mass flow rate returns to the flow rate value of the stable casting stage.

[0029] Specifically, during the steady-state casting stage, the inlet mass flow rate equals the sum of all outlet mass flow rates. This setting aims to simulate steady-state operation during continuous casting, ensuring a constant molten steel level in the tundish. Specifically, the total outlet mass flow rate can be determined by calculating the casting speed and cross-sectional dimensions of each stream, and the inlet mass flow rate can be precisely set to this calculated value. Alternatively, a level control system can be used to dynamically balance the inlet and outlet flow rates by monitoring the tundish level in real time and adjusting the opening of the long nozzle or the ladle flow rate accordingly, thereby maintaining a stable level. During the lowering stage, the inlet mass flow rate is zero. This setting simulates the transition period between the completion of casting the old steel grade and the pre-filling of the new steel grade. During this stage, the ladle stops supplying steel to the tundish, and the molten steel in the tundish flows into the crystallizer only through the submerged entry nozzle, causing the level to gradually decrease. In numerical simulations, this is typically achieved by directly setting the mass flow rate boundary condition of the long nozzle to zero to accurately reflect the physical process of molten steel stopping injection. During the rising stage, the inlet mass flow rate is set to a constant first flow rate value greater than the steady-state casting flow rate. This setting simulates the process of rapidly injecting a new steel grade into the tundish to raise the liquid level. To accelerate liquid level recovery and promote the mixing of new and old steel grades, the injection flow rate of the new steel grade is usually higher than the flow rate during normal stable casting. For example, a fixed, relatively large flow rate value can be preset as the first flow rate value, such as 72 kg / s, 90 kg / s, or 108 kg / s, based on the tundish volume, the target liquid level rise rate, and the stable casting flow rate, to ensure a rapid recovery of the liquid level. After the liquid level stabilizes, the inlet mass flow rate returns to the flow rate value of the aforementioned stable casting stage. This setting indicates that after the tundish liquid level reaches the preset stable working level, the casting operation returns to the normal steady-state mode. At this time, the inlet mass flow rate will be adjusted back to a value equal to the sum of all outlet mass flow rates to maintain continuous liquid level stability and provide a stable supply of molten steel for subsequent continuous casting processes.

[0030] By setting the specific mass flow rates described above, this application can accurately simulate the dynamic flow behavior of molten steel in the tundish during continuous casting of dissimilar steel grades. During the stable casting stage, balancing the inlet and outlet mass flow rates ensures the steady-state accuracy of the simulation. During the liquid level reduction stage, setting the inlet mass flow rate to zero realistically reflects the consumption of the old steel grade and the decrease in liquid level. During the liquid level raising and ladle filling stage, using a first flow rate value greater than the stable casting flow rate effectively simulates the dynamic process of rapid injection of the new steel grade, rapid recovery of the liquid level, and intense mixing of the old and new steel grades. After the liquid level stabilizes, the flow rate returns to the stable casting value, ensuring the continuity and stability of subsequent simulations. These precise flow rate settings serve as boundary conditions for the aforementioned tundish multiphase flow mathematical model, enabling the model to more accurately capture the flow, mass transfer, and interfacial behavior of molten steel, covering agent, and air during different continuous casting stages. This significantly improves the accuracy and reliability of predicting the composition and calculating the length of dissimilar steel mixed-cast billets, providing a solid data foundation for optimizing process parameters and shortening the length of mixed-cast billets.

[0031] As an example, the solidification and mass transfer coupling model of the billet is a 1 / 4 symmetric model established for a 160mm×160mm cross-section square billet.

[0032] Specifically, this coupled solidification and mass transfer model for billets aims to accurately simulate the continuous casting process of billets of a specific size. A quarter-symmetric model is employed based on the symmetry of the billet's geometry and physical processes (such as flow, heat transfer, and solidification). This symmetry allows the complex full-size three-dimensional computational domain to be simplified to one-quarter, significantly reducing the number of meshes and computational resources required. For example, besides the quarter-symmetric model, a half-symmetric model can be used for billets with a single plane of symmetry; or in certain special cases, if significant asymmetry exists, a full-size three-dimensional model may be necessary. However, for conventional billets, the quarter-symmetric model significantly improves computational efficiency while maintaining simulation accuracy.

[0033] In summary, the 1 / 4 symmetric model established for the 160mm×160mm cross-section billet fully utilizes the geometric symmetry of the billet, effectively reducing the computational domain and thus significantly reducing the number of meshes and computational complexity required for the calculation. While ensuring the accuracy of the simulation, it greatly improves the computational efficiency.

[0034] This application further proposes the governing equations of the billet solidification and mass transfer coupling model, including the continuity equation, momentum conservation equation, turbulence model equation, component transport equation, and energy conservation equation including latent heat treatment in solidification. In the boundary conditions of the billet solidification and mass transfer coupling model, the heat flux density boundary varies with position in the crystallizer region, and the convective heat transfer boundary is adopted in the secondary cooling region.

[0035] Specifically, the governing equations of the coupled solidification and mass transfer model jointly describe the complex physical behavior of molten steel during continuous casting. Among them, the continuity equation describes the mass conservation of molten steel, ensuring that the mass does not increase or decrease within the computational domain; the momentum conservation equation, i.e., the Navier-Stokes equation, describes the momentum conservation of molten steel, reflecting the flow state of molten steel under various forces (such as pressure gradients, viscous forces, and gravity); the turbulence model equations capture the turbulent characteristics of molten steel during continuous casting, for example, the standard k-ε model, the RNG k-ε model, or the Realizable k-ε model can be used to more accurately describe the influence of turbulent viscosity on the flow field; and the component transport equations describe the convection and diffusion processes of key elements (such as carbon) in molten steel, thereby predicting their distribution in the billet. In particular, the energy conservation equation, which includes the latent heat of solidification treatment, is crucial for simulating the solidification process. A large amount of latent heat of solidification is released when molten steel transitions from a liquid to a solid state. This equation precisely addresses this heat change by introducing a latent heat term (e.g., through enthalpy or source terms), ensuring accurate prediction of the temperature field and thus influencing the growth of the solidified shell and element transport.

[0036] Furthermore, the boundary conditions of the coupled solidification and mass transfer model of the billet are crucial for connecting the model with the actual physical environment. The crystallizer region employs a position-varying heat flux density boundary. The crystallizer is the region where the billet initially solidifies, and its cooling intensity is not uniform along the casting direction. Using a position-varying heat flux density boundary more realistically reflects the complex heat transfer process between the inner wall of the crystallizer and the billet. For example, this varying heat flux density distribution can be determined through empirical formulas, experimental measurements, or coupled calculations with the flow of cooling water in the crystallizer. The secondary cooling region employs a convective heat transfer boundary. The secondary cooling region primarily cools the billet through water spray. Using convective heat transfer boundary conditions can simulate the convective heat transfer effect of water spray cooling on the billet surface. For example, different heat transfer coefficients can be set to characterize the influence of parameters such as spray intensity and water temperature on the cooling effect, or a more complex spray cooling model can be used to calculate the heat transfer coefficient.

[0037] Through the above technical solutions, the billet solidification and mass transfer coupling model of this application can simulate the continuous casting process more accurately and efficiently. In the governing equations, in addition to the continuity equation, momentum conservation equation, turbulence model equation, and component transport equation, an energy conservation equation incorporating latent heat treatment is specifically introduced. This allows the model to accurately capture the release and absorption of latent heat of phase transformation during the solidification process of molten steel, avoiding temperature field prediction deviations caused by neglecting latent heat effects, thereby significantly improving the accuracy of predicting the transport of key elements and the final composition distribution within the billet. Furthermore, in terms of boundary condition settings, the crystallizer region uses a location-varying heat flux density boundary, which can realistically reflect the uneven heat flux distribution within the crystallizer, while the secondary cooling region uses a convective heat transfer boundary, which can accurately reproduce the dynamic heat exchange process of water spray cooling. These refined boundary condition settings ensure that the heat transfer simulation results are highly consistent with industrial practice, effectively reducing errors introduced by boundary simplification, and ultimately ensuring the reliability of the predicted composition and length of the mixed-cast billet, providing a solid foundation for the optimized control of mixed-cast billets of dissimilar steels in continuous casting.

[0038] This application further proposes physical simulation verification, including: establishing a tundish water model based on similarity criteria, measuring the outlet tracer concentration change curve, and comparing it with the simulation results of the tundish multiphase flow mathematical model.

[0039] Physical simulation verification is a crucial means of ensuring the reliability of numerical simulation results. It involves constructing a scaled-down or scaled-up model with similar physical properties to the actual system, reproducing or simulating the actual process under controlled experimental conditions, thereby obtaining experimental data. This data can be directly compared with the numerical simulation results to evaluate the accuracy and applicability of the numerical model. Its role is to provide experimental evidence independent of numerical computation, enhancing confidence in the predictive power of the mathematical model. Besides water models, other fluid models such as gas or oil models can also be used for physical simulations, as long as they meet similarity criteria and reflect key fluid dynamic behaviors.

[0040] Establishing a tundish water model based on similarity criteria involves designing and constructing a transparent model with a geometry similar to the actual tundish, but typically smaller in size, based on a series of dimensionless parameters (such as Froude number and Reynolds number), and using water as the simulated fluid. This process aims to ensure that the physical model and the actual prototype are similar in fluid dynamics, heat transfer, and mass transfer, thereby enabling direct observation and measurement of the flow patterns and mixing behavior of the molten steel inside the tundish, providing macroscopic and microscopic experimental data for the verification of the numerical model. In addition to geometric similarity, kinematic and dynamic similarity must also be ensured to accurately replicate the fluid behavior of the actual tundish.

[0041] Measuring the tracer concentration change curve at the outlet involves injecting a readily detectable substance (i.e., the tracer) that does not affect the main physicochemical properties of the fluid into the inlet of the "new steel grade" in the water model, and monitoring the change in tracer concentration at the water model outlet over time. By measuring the tracer concentration change curve, the mixing degree and replacement rate of the new and old fluids (simulating the new and old steel grades) in the tundish can be quantified. This curve visually reflects the residence time distribution and mixing efficiency of the fluid in the tundish, and is a key indicator for evaluating the flow field and mixing behavior in the tundish. The tracer can be an electrolyte solution (concentration measured by conductivity), a dye (concentration measured by light absorption or color change), or a pH-sensitive substance (concentration measured by pH value).

[0042] Comparing the simulation results with the mathematical model of multiphase flow in the tundish involves comparing the outlet tracer concentration change curve obtained through water model experiments with the concentration change curve predicted by the mathematical model of multiphase flow in the tundish under the same boundary conditions and process parameters. This comparison is a core step in verifying the accuracy of the mathematical model. By comparing the shape of the curves, the rate of rise, the time to reach a stable concentration, and the final concentration value, the predictive ability of the mathematical model for the fluid mixing behavior in the tundish can be evaluated. If the two match well, it indicates that the mathematical model can accurately reflect the actual process; if there are deviations, the mathematical model needs to be corrected and optimized. Comparison methods can include qualitative comparisons (such as curve trends and peak positions) and quantitative comparisons (such as calculating the root mean square error and correlation coefficient).

[0043] This application further proposes industrial test verification including: conducting continuous casting tests of different steel grades at the production site, sampling and detecting the changes in the content of key elements over time, and comparing the results with the prediction results of the tundish multiphase flow mathematical model or the billet solidification and mass transfer coupling model.

[0044] Specifically, conducting continuous casting tests of different steel grades on the production site aims to simulate the steel grade switching process in an actual production environment, ensuring the authenticity and representativeness of the verification data. For example, on a continuous casting production line, a continuous casting switching operation from an old steel grade to a new steel grade can be performed according to a predetermined process flow. Specific steel grades (such as C62DA and C72DA) can be selected for continuous casting, and their production conditions can be recorded, such as 25 tons of steel remaining in the tundish and a casting speed of 2.2 meters per minute. Alternatively, historical continuous casting events of different steel grades that have occurred can be used as sources of verification test data. By conducting tests in an actual production environment, various complex metallurgical phenomena and operational factors can be fully considered, avoiding the limitations of laboratory simulations, thus making the verification data more convincing.

[0045] During the aforementioned experiments, it is necessary to sample and test the content of key elements to obtain actual data on their changes over time. This step aims to directly capture the dynamic distribution of key elements during the mixing of new and old steel grades. For example, periodic sampling can be used, collecting molten steel or billet samples at preset time intervals at the tundish outlet or different locations on the billet. Subsequently, using specialized analytical equipment, such as a spectrometer or chemical analyzer, the mass fraction of key elements (e.g., carbon, or other alloying elements such as manganese, chromium, and nickel) in the samples is accurately determined. By continuously monitoring the changes in the content of key elements, the degree of mixing and transition zone between new and old steel grades can be intuitively reflected, providing a quantitative basis for model verification.

[0046] Data on the actual changes in the content of key elements over time, obtained through industrial trials, will be compared with the prediction results of the aforementioned tundish multiphase flow mathematical model or the aforementioned billet solidification and mass transfer coupling model. This comparison aims to quantitatively evaluate the accuracy and reliability of the model. Specifically, the measured element concentration-time curves can be overlaid with the predicted curves output by the model. The degree of agreement between the curves can be visually observed, or the deviation between the two can be quantified by calculating statistical indicators (such as root mean square error, correlation coefficient, etc.). For example, the measured values ​​of the mass fraction of element C over time in industrial trials can be compared with the predicted curves from numerical simulations to verify the accuracy of the model. If significant deviations exist, the model's parameter settings, boundary conditions, or turbulence model can be adjusted and optimized based on the comparison results, thereby improving the model's prediction accuracy and applicability, and ensuring that the model accurately reflects the actual production situation.

[0047] In one alternative implementation, different combinations of process parameters include different amounts of residual steel in the tundish, different continuous casting speeds, and different ladle filling flow rates for new steel grades.

[0048] As an example, the remaining steel in the tundish includes 20 tons, 25 tons, and 30 tons; the continuous casting speed includes 2.5 m / min, 2.8 m / min, and 3.0 m / min; and the ladle filling flow rate for new steel grades includes 72 kg / s, 90 kg / s, and 108 kg / s.

[0049] This application further proposes to analyze the influence of process parameters on the mixing behavior in the tundish, and determines the following rules: the amount of residual steel in the tundish is the dominant factor affecting the replacement rate of old and new steel grades; the smaller the amount of residual steel, the faster the replacement rate; the casting speed of continuous casting has a slight influence on the mixing process after the filling period; the higher the casting speed, the faster the concentration of new steel grade increases in the later stage of mixing; the filling flow rate of new steel grade mainly accelerates the mixing of old and new steel grades during the filling period, and has a limited impact on the overall mixing process after the filling period.

[0050] The analysis of the impact of process parameters on the mixing behavior in the tundish aims to gain a deeper understanding of how different operating conditions affect the steel mixing process within the tundish, thereby providing a scientific basis for optimizing process parameters and shortening the length of the mixed billet. This analysis can be achieved in several ways. For example, numerical simulation methods can be used to establish a mathematical model of multiphase flow in the tundish, simulating the flow, mass transfer, and interfacial behavior of molten steel, covering agent, and air under different combinations of process parameters, thereby obtaining data on the concentration changes of new steel grades at the tundish outlet. Alternatively, physical simulation methods can be used to establish a tundish water model based on similarity criteria, and the outlet tracer concentration change curve can be measured through tracer experiments. Another approach is to conduct industrial trials, carrying out continuous casting tests of different steel grades in actual production sites, and sampling to detect changes in the content of key elements over time.

[0051] Based on the analysis, identifying the aforementioned patterns refers to revealing the intrinsic relationship and quantitative impact between process parameters and mixing behavior through in-depth processing and summarization of simulation or experimental data. This can include statistical analysis and regression modeling of the data to establish the mathematical relationship between parameters and mixing efficiency; it can also be achieved by comparing the concentration change curves and diffusion cloud maps of new steel grades under different parameter conditions to identify the qualitative or semi-quantitative influence trends of parameters on the mixing rate and degree of mixing of new and old steel grades.

[0052] Specifically, the residual steel volume in the tundish refers to the amount of old steel remaining in the tundish before the new steel grade is poured during continuous casting of dissimilar steel grades. It is typically expressed in tons or liquid level. This residual steel volume is the dominant factor affecting the replacement rate of the old and new steel grades; the smaller the residual steel volume in the tundish, the smaller the mixing volume of the old and new steel grades, and the faster the new steel grade dilutes and replaces the old steel grade. The replacement rate of the old and new steel grades can be measured by monitoring the rate of change of the dimensionless concentration of the new steel grade at the tundish outlet over time.

[0053] Continuous casting speed refers to the speed at which the continuous casting machine pulls out the billet, usually expressed in meters per minute (m / min). It directly determines the flow rate of molten steel through the tundish. Continuous casting speed has a slight impact on the mixing process after the ladle filling period. Specifically, after the molten steel level in the tundish stabilizes, a higher casting speed results in a relatively shorter residence time of the molten steel in the tundish, which helps to slightly accelerate the increase in the concentration of new steel grades in the later stages of mixing.

[0054] The new steel grade filling flow rate refers to the flow rate at which the new steel grade begins to be injected into the tundish to restore the liquid level to a stable working height. It is typically higher than the stable casting flow rate. This filling flow rate primarily accelerates the mixing of the new and old steel grades during the filling process, as the higher flow rate generates stronger impact and turbulence, promoting rapid mixing within a short time. However, once the filling process is complete and the tundish flow rate returns to the stable casting flow rate, the filling flow rate has limited impact on the subsequent overall mixing process.

[0055] Through the above technical solution, this application can clearly distinguish the degree and mechanism of influence of different process parameters on the continuous casting and mixing behavior of dissimilar steels, solving the problem of lack of quantitative guidance in process parameter analysis. By identifying the amount of residual steel in the tundish as the dominant factor and clarifying its negative correlation with the replacement rate, process adjustments can prioritize reducing the amount of residual steel, thereby directly and efficiently accelerating the transition between old and new steel grades. Simultaneously, the quantification of the impact of continuous casting speed and the ladle filling flow rate of the new steel grade avoids excessive attention to secondary factors and unnecessary adjustments, making process optimization more targeted and efficient. This precise understanding of the influence of process parameters can effectively guide production operations, achieving precise control with the goal of shortening the length of mixed-cast billets, thereby reducing the generation of defective products and lowering production costs.

[0056] This application further proposes an analysis of slag entrapment risk determination: for tundishes, the minimum safe molten steel level to avoid vortex slag entrapment is at least 40 mm above the bottom of the ladle.

[0057] The "Analysis and Determination of Slag Entrainment Risk" step aims to identify and quantify the likelihood and critical conditions of slag entrainment in molten steel under specific operating conditions. Its purpose is to provide a theoretical basis and safety thresholds for subsequent process parameter setting, ensuring that product quality is not sacrificed while optimizing production efficiency. Specifically, a multiphase flow mathematical model of molten steel flow and slag behavior within the tundish can be established to simulate the changes in the molten steel flow field at different liquid level heights, particularly the flow field near the submerged entry nozzle, thereby predicting the formation and development of vortices and determining the critical liquid level height leading to slag entrainment. Alternatively, physical simulation experiments, such as using a water model or a transparent tundish model, can be conducted to observe and record the formation of vortices at the submerged entry nozzle and the phenomenon of slag entrainment at different liquid level heights, thereby directly determining the minimum safe liquid level height to avoid slag entrainment.

[0058] The phrase "for the tundish" indicates that the determined minimum safe molten steel level is specific to a tundish with a particular structure and size. Different tundish geometries, flow control devices (such as baffles and turbulence suppressors), and the design of the submerged entry nozzle all affect the flow field of the molten steel and the critical conditions for vortex slag entrainment. Therefore, this feature emphasizes the applicability and customization of the solution. The tundish can be a five-strand billet tundish with internal flow control devices such as perforated baffles and turbulence suppressors, and has specific geometric dimensions and volume.

[0059] The specific value of "the minimum safe molten steel level to avoid vortex slag entrainment is 40mm or more from the bottom of the ladle" is an operational threshold determined after rigorous analysis and verification, designed to guide tundish level control. Its core function is to effectively suppress turbulence in the molten steel flow field in the submerged entry nozzle area by consistently maintaining the molten steel level above 40mm from the ladle bottom, preventing the formation of vortices large enough to entrain slag, thus ensuring the cleanliness of the molten steel during continuous casting. This 40mm value is based on the results of multiphase flow numerical simulations of a specific tundish structure. The simulations analyzed the molten steel velocity field, eddy current distribution, and slag behavior near the submerged entry nozzle at different liquid level heights, accurately identifying the critical liquid level at which vortex slag entrainment occurs, and setting a safety margin based on this.

[0060] This application further proposes to analyze the impact of key process parameters on the cleanliness risk of molten steel and determines the following rules: the smaller the amount of residual steel in the tundish, the larger the exposed area of ​​molten steel and the longer the time during the filling stage; the smaller the filling flow rate of the new steel grade, the smaller the exposed area of ​​molten steel during the filling stage.

[0061] The finding that "the smaller the amount of residual steel in the tundish, the larger the exposed area and the longer the time of molten steel during the filling stage" reveals the influence of the amount of molten steel remaining in the tundish after the casting of the old steel grade on the exposed steel behavior. The residual steel in the tundish refers to the amount of molten steel remaining in the tundish after the casting of the old steel grade during continuous casting of different steel grades. This amount directly determines the initial height of the molten steel surface in the tundish when the new steel grade is poured. When the residual steel in the tundish is small, the molten steel surface in the tundish is lower when the new steel grade is poured, the impact distance of the molten steel from the long nozzle into the tundish is increased, the impact kinetic energy of the molten steel on the slag layer is greater, and it is easier to break through the slag layer, forming a larger exposed area of ​​molten steel. Furthermore, a lower residual steel in the tundish may lead to a longer time required to reach a stable molten steel surface, thus prolonging the time the molten steel is exposed to air. Another scenario is that when the amount of residual steel is too low, for example, when the slag liquid level is lower than the bottom of the long nozzle, the air rushing out from the long nozzle may not completely flow into the molten steel, but will be directly discharged into the air. However, the subsequent molten steel will still carry the air and continue to be injected, resulting in an increase in the number of tiny bubbles dispersed in the injection zone. Furthermore, the thin slag layer is more easily separated by the rising molten steel, thereby increasing the exposed area of ​​the molten steel.

[0062] The principle that "the smaller the flow rate of the new steel grade in the ladle, the smaller the exposed area of ​​the molten steel during the filling stage" clarifies the impact of the flow rate of the new steel grade injected into the tundish on the exposed steel behavior. The flow rate of the new steel grade in the ladle refers to the mass flow rate of molten steel from the long nozzle of the ladle into the tundish when the new steel grade begins to be injected during continuous casting of different steel grades. A smaller flow rate means that the kinetic energy of the new steel grade injected into the tundish is relatively low, reducing the impact on the slag layer on the tundish surface. This helps maintain the integrity and stability of the slag layer, reducing the possibility of the slag layer being washed away, forming an exposed area of ​​molten steel. At the same time, a lower flow rate can reduce the turbulence intensity of the molten steel in the tundish, reduce the contact area between the molten steel and air, thereby effectively inhibiting secondary oxidation of the molten steel and reducing the risk of air entrainment into the molten steel.

[0063] Through the above technical solution, this method can provide precise guidance for the selection of process parameters in the continuous casting of different steel grades, thereby effectively controlling the cleanliness of molten steel.

[0064] This application further proposes that the key element is carbon; the method for calculating the length of the mixed billet is as follows: a judgment range is set according to the internal control standards of carbon for the new and old steel grades, and the length of the billet segment whose carbon mass fraction falls outside the judgment range of the new and old steel grades is counted as the length of the mixed billet.

[0065] Carbon is the key element because it plays a central role in the properties and classification of steel, directly affecting its hardness, strength, toughness, weldability, and other critical mechanical properties. In the continuous casting of dissimilar steels, differences in carbon content are often one of the main criteria for distinguishing different steel grades. Therefore, monitoring and predicting carbon as a key element can effectively reflect the degree of mixing between new and old steel grades. Besides carbon, in other implementations, other elements such as manganese, silicon, phosphorus, sulfur, chromium, nickel, molybdenum, and vanadium can be selected as key elements, or multiple elements can be selected for comprehensive determination, depending on the specific steel type and production requirements.

[0066] Setting judgment ranges based on the internal control standards for carbon content in old and new steel grades refers to defining an acceptable range for carbon content according to the quality control requirements of a specific steel grade. For example, for the old steel grade 45#, the internal control standard for carbon content might be set at 0.42% to 0.5%; for the new steel grade 65#, the internal control standard might be set at 0.62% to 0.7%. These internal control standards are usually determined by steel mills based on factors such as product application, customer requirements, and national standards, and are important criteria for assessing the quality of steel. By setting these judgment ranges, it is possible to clearly distinguish between pure old steel grade areas and pure new steel grade areas, providing an objective basis for the subsequent identification of mixed-cast billets. In practical applications, these judgment ranges can be flexibly adjusted according to specific steel grades, production processes, and quality requirements to adapt to different production scenarios.

[0067] The length of a slab segment whose carbon content falls outside the determination range for old and new steel grades is counted as the mixed-cast slab length. This refers to the process of continuously casting, where the carbon content in the slab is predicted in real time through monitoring or simulation, and compared with the preset carbon content determination range for old and new steel grades. If the carbon content of a certain slab segment meets neither the determination range for the old steel grade nor the determination range for the new steel grade, then that slab segment is considered a mixed-cast slab. For example, if the carbon content range of the old steel grade is... The carbon content range of the new steel grade is Then, when the carbon mass fraction C at a certain point in the billet satisfies or or When the specified point is reached, the corresponding slab segment is identified as a mixed-cast slab. By summing the lengths of all slab segments identified as mixed-cast slabs, the total length of the mixed-cast slab can be obtained. This method provides an objective standard for quantifying the degree of mixing, avoiding errors caused by subjective judgment.

[0068] The above technical solution explicitly defines carbon as the key element and details the calculation method for the length of mixed-cast billets, thus solving the problems of unclear key element selection and lack of unified standards for length calculation methods in the process of predicting the composition and calculating the length of mixed-cast billets of dissimilar steels. Specifically, by using carbon as the key element and utilizing its significant content differences among different steel grades, the mixing state of new and old steel grades can be accurately captured. Simultaneously, by setting a judgment range for carbon content based on the internal control standards of new and old steel grades, and using the billet segment with carbon mass fraction falling outside these judgment ranges as the mixed-cast billet, an objective and quantitative standard for calculating the length of mixed-cast billets is provided. This makes the prediction and calculation of mixed-cast billet length more accurate and consistent, avoiding the uncertainty caused by subjective judgment, thereby more effectively guiding production, optimizing process parameters, reducing scrap or downgraded products caused by mixed casting, and significantly improving the economic benefits and product quality control level of the dissimilar steel continuous casting process.

[0069] This application further quantifies the impact of different process parameters on the length of the mixed-cast billet through simulation calculations. Specifically, the simulation calculations show that: under different amounts of residual steel in the tundish, the length of the mixed-cast billet varies significantly; reducing the amount of residual steel from 30 tons to 20 tons can shorten the length of the mixed-cast billet by more than 10 meters; under different continuous casting speeds, the difference in the length of the mixed-cast billet is less than 2.2 meters; under different new steel grades and filling flow rates, the change in the length of the mixed-cast billet is less than 4.5 meters and there is no consistent pattern of change.

[0070] The simulation calculations are based on established and validated mathematical models of multiphase flow in the tundish and coupled models of solidification and mass transfer in the billet. Their purpose is to predict the composition distribution and length of mixed-cast billets of dissimilar steels under different process conditions using numerical methods, thereby obtaining quantitative data. This can be achieved using specialized computational fluid dynamics (CFD) software, such as ANSYS Fluent, or simulation platforms specifically developed for metallurgical processes, to ensure the accuracy and reliability of the simulation results. Tundish residual steel refers to the amount of molten steel remaining in the tundish after the old steel casting is completed and the new steel casting begins during the continuous casting of dissimilar steel grades. The simulation results reveal that the tundish residual steel has a significant impact on the length of the mixed-cast billet and provide specific quantitative data. For example, different residual steel amounts can be achieved by adjusting the timing of ladle replacement or controlling the initial liquid level in the tundish. This quantitative result clearly indicates that reducing the tundish residual steel is a key way to effectively shorten the length of the mixed-cast billet. Continuous casting speed refers to the speed at which the continuous casting machine pulls the billet out of the mold. The simulation results quantify the impact of continuous casting speed on the length of the mixed billet, indicating that its influence is relatively small. The continuous casting speed can be adjusted by controlling the speed of the continuous casting machine's drive mechanism or by regulating the flow rate of the submerged entry nozzle. This finding helps to treat continuous casting speed as a secondary consideration in the optimization process. The new steel grade filling flow rate refers to the flow rate of molten steel of the new steel grade when it is injected from the ladle into the tundish. The simulation results quantify the impact of the new steel grade filling flow rate on the length of the mixed billet and indicate that its variation pattern is inconsistent. The filling flow rate can be controlled by adjusting the opening of the ladle slide or stopper. This result shows that the overall impact of the new steel grade filling flow rate on the length of the mixed billet is limited and difficult to predict; therefore, it should not be considered a primary adjustment parameter in the optimization strategy.

[0071] Through the above simulation calculations, this application quantifies the specific impact of three key process parameters—the amount of residual steel in the tundish, the continuous casting speed, and the filling flow rate of the new steel grade—on the length of the mixed-cast billet. Specifically, the simulation results clearly indicate that the amount of residual steel in the tundish is the dominant factor affecting the length of the mixed-cast billet; its change can significantly shorten the length of the mixed-cast billet. For example, reducing the amount of residual steel from 30 tons to 20 tons can shorten the length of the mixed-cast billet by more than 10 meters. In contrast, the continuous casting speed has a weak impact on the length of the mixed-cast billet, with a difference of less than 2.2 meters; while the impact of the filling flow rate of the new steel grade is even more limited and shows no consistent pattern, with a change of less than 4.5 meters. These quantitative data provide a precise basis for the composition prediction and length calculation method of continuously cast mixed-cast billets of dissimilar steel grades. This allows for a targeted focus on the dominant factors when determining the optimal process control parameters, such as prioritizing the adjustment of the amount of residual steel in the tundish, thereby efficiently and accurately shortening the length of the mixed-cast billet, effectively reducing the generation of defective products, lowering production costs, and improving production efficiency.

[0072] This application further proposes the following principle for determining the optimal process control parameters: on the premise of ensuring that the molten steel level is higher than the guide hole and not lower than the minimum safe molten steel level, the amount of residual steel in the tundish should be reduced to the minimum.

[0073] Regarding ensuring the molten steel level is above the guide hole, this technical feature aims to ensure that the molten steel level in the tundish is always maintained above the guide hole. Specifically, during continuous casting of different steel grades, the molten steel level in the tundish is monitored in real time, and combined with preset guide hole position parameters, the molten steel level is ensured not to be lower than the upper edge of the guide hole. For example, a level sensor (such as an electromagnetic, float, or laser level gauge) can be used to continuously monitor the molten steel level in the tundish, and the monitoring data can be fed back to the control system. When the molten steel level tends to drop to the height of the guide hole, the control system can issue an early warning or automatically adjust the flow rate at the ladle outlet to maintain the molten steel level above the guide hole. Alternatively, the tundish structural design can be optimized, such as adjusting the height or shape of the guide hole, to effectively prevent slag flow even at lower molten steel levels, thereby preventing slag from flowing from the pouring zone to the casting zone and preventing the risk of exposed molten steel due to uneven slag layer thickness.

[0074] Regarding the minimum safe molten steel level, this technical feature aims to prevent vortex slag entrapment that may occur when the molten steel level in the tundish is too low. The minimum safe molten steel level is a critical value determined based on the tundish structure and hydrodynamic characteristics; below this value, vortex slag entrapment is highly likely to occur. For example, based on physical or numerical simulation results, it can be determined that for a specific tundish, the minimum safe molten steel level to avoid vortex slag entrapment is at least 40mm above the bottom of the ladle. In actual operation, the molten steel volume in the tundish is precisely controlled to ensure it never falls below this minimum safe molten steel level. This can be achieved by setting a lower limit for the molten steel level alarm or an automatic stop / deceleration mechanism. Once the molten steel level approaches or reaches this critical value, the system will take measures to prevent further decline, thereby effectively eliminating the possibility of vortex slag entrapment and ensuring the cleanliness of the molten steel.

[0075] Regarding minimizing the residual steel in the tundish, this technical feature aims to reduce the amount of old steel grade remaining in the tundish to accelerate the replacement speed of old and new steel grades. Under the premise of meeting the aforementioned steel level safety constraints, the residual steel in the tundish during steel grade switching is controlled to the lowest permissible level by optimizing process parameters. For example, based on process conditions such as different steel grades, different continuous casting speeds, and different new steel grade filling flow rates, numerical simulations or industrial tests can be used to determine the minimum residual steel amount that can achieve the shortest mixed billet length while ensuring the steel level is above the guide hole and not below the minimum safe liquid level. In actual production, operators or automated systems will precisely control the residual steel in the tundish to this minimum value before steel grade switching according to a preset optimization strategy, thereby maximizing production efficiency while ensuring steel quality.

[0076] Through the above technical solution, this application can effectively balance the relationship between shortening the length of the mixed-cast billet and ensuring the cleanliness of the molten steel during the continuous casting process of different steel grades. Specifically, by ensuring that the molten steel level is higher than the guide hole, it can effectively prevent slag from flowing from the pouring area to the casting area during the process of lowering or raising the liquid level, avoiding the risk of exposed molten steel caused by uneven slag layer thickness, thereby reducing secondary oxidation and slag inclusions in the molten steel. At the same time, by ensuring that the molten steel level is not lower than the minimum safe liquid level height, the possibility of vortex slag entrapment can be completely eliminated, maintaining the stability of the molten steel level, further ensuring the cleanliness of the molten steel, and avoiding the decline in billet quality caused by slag entrapment. Under this dual safety constraint, the amount of residual steel in the tundish is reduced to a minimum, which can minimize the residual amount of old steel grades, significantly accelerate the mixing and replacement process of new and old steel grades, and thus effectively shorten the length of the mixed-cast billet. Overall, this solution achieves the minimization of the length of the mixed-cast billet while ensuring the quality of the billet and the cleanliness of the molten steel, improving production efficiency and reducing production costs.

[0077] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for predicting the composition and calculating the length of dissimilar steel continuously cast billets, characterized in that, include: S1. Establish a mathematical model of multiphase flow in the tundish to simulate the flow, mass transfer and interfacial behavior of molten steel, covering agent and air during the continuous casting of different steel grades. S2. Establish a coupled model of billet solidification and mass transfer to simulate the flow, solidification, heat transfer and transport of key elements of the billet during continuous casting. S3. The mathematical model of multiphase flow in the tundish and the coupling model of solidification and mass transfer of the billet are verified by physical simulation and industrial test data. S4. Based on the verified mathematical model of multiphase flow in the tundish, simulate the continuous casting process of different steel grades under different combinations of process parameters, obtain the concentration change data of new steel grades at the tundish outlet, and analyze the influence of process parameters on the mixing behavior in the tundish. S5. Based on the multiphase flow simulation results of the tundish multiphase flow mathematical model, analyze the impact of key process parameters on the exposure of molten steel in the injection zone, slag layer distribution and slag entrapment risk during the liquid level drop and liquid level rise processes. S6. Use the concentration change data of the new steel grade at the outlet of the tundish as the input boundary condition of the solidification and mass transfer coupling model of the billet, simulate and predict the distribution of key elements in the mixed billet, and calculate the length of the mixed billet. S7. Based on the combined analysis results of the risk assessment of the length of the mixed billet and the cleanliness of the molten steel, determine the optimal process control parameters with the goal of shortening the length of the mixed billet.

2. The method according to claim 1, characterized in that, The governing equations of the intermediate batch multiphase flow mathematical model include the continuity equation, momentum conservation equation, turbulence model equation, component transport equation, and VOF multiphase flow equation. In the boundary conditions of the mathematical model for multiphase flow in the tundish, the inlet boundary adopts the mass flow rate that changes dynamically according to the continuous casting stage, and the outlet boundary adopts the mass flow rate that changes according to the casting speed.

3. The method according to claim 1, characterized in that, The governing equations of the billet solidification and mass transfer coupling model include the continuity equation, the momentum conservation equation, the turbulence model equation, the component transport equation, and the energy conservation equation including the latent heat of solidification treatment. In the boundary conditions of the casting solidification and mass transfer coupling model, the crystallizer region adopts a heat flux density boundary that varies with position, and the secondary cooling region adopts a convective heat transfer boundary.

4. The method according to claim 1, characterized in that, The different combinations of process parameters include different amounts of residual steel in the tundish, different continuous casting speeds, and different ladle filling flow rates for new steel grades.

5. The method according to claim 4, characterized in that, The influence of process parameters on the mixing behavior in the tundish was analyzed, and the following patterns were determined: The amount of residual steel in the tundish is the dominant factor affecting the replacement speed of old and new steel grades; the smaller the amount of residual steel, the faster the replacement speed. The continuous casting speed has a slight impact on the mixing process after the ladle filling period. The higher the casting speed, the faster the concentration of the new steel grade increases in the later stage of mixing. The new steel grade filling flow rate mainly accelerates the mixing of new and old steel grades during the filling process, and has a limited impact on the overall mixing process after the filling is completed.

6. The method according to claim 1, characterized in that, The impact of key process parameters on the cleanliness risk of molten steel was analyzed, and the following patterns were identified: The smaller the amount of steel remaining in the tundish, the larger the exposed area of ​​molten steel and the longer the time during the filling stage. The smaller the ladle flow rate of the new steel grade, the smaller the exposed area of ​​molten steel during the ladle filling stage.

7. The method according to claim 1, characterized in that, The key element is carbon. The method for calculating the length of the mixed-cast billet is as follows: a judgment range is set according to the internal control standards for carbon elements of the new and old steel grades, and the length of the billet segment whose carbon element mass fraction falls outside the judgment range of the new and old steel grades is counted as the length of the mixed-cast billet.

8. The method according to claim 1, characterized in that, The principle for determining the optimal process control parameters is to minimize the amount of residual steel in the tundish while ensuring that the molten steel level is above the guide hole and not below the minimum safe molten steel level.

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