Final Electromagnetic Stirring Research Articles

Numerical Simulation of Fluid Flow, Solidification, and Solute Distribution in Billets under Combined Mold and Final Electromagnetic Stirring.

In this study, a three-dimensional segmented coupled model for continuous casting billets under combined mold and final electromagnetic stirring (M-EMS, F-EMS) was developed. The model was verified by comparing carbon segregation in billets with and without EMS through plant experiments. The findings revealed that both M-EMS and F-EMS induce tangential flow in molten steel, impacting solidification and solute distribution processes within the billet. For M-EMS, with operating parameters of 250A-2Hz, the maximum tangential velocity (velocity projected onto the cross-section) was observed at the liquid phase's edge. For F-EMS, with operating parameters of 250A-6Hz, the maximum tangential velocity occurred at fl=0.7. Furthermore, F-EMS accelerated heat transfer in the liquid phase, reducing the central liquid fraction from 0.93 to 0.85. M-EMS intensified the washing effect of molten steel on the solidification front, resulting in the formation of negative segregation within the mold. F-EMS significantly improved the centerline segregation issue, reducing carbon segregation from 1.15 to 1.02. Experimental and simulation results, with and without EMS, were in good agreement, indicating that M+F-EMS leads to a more uniform solute distribution within the billet, with a pronounced improvement in centerline segregation.

Multiphase Solidification Modeling of Solidification Structure Evolution and Macrosegregation of Round Bloom Continuous Casting Process with Mold Electromagnetic Stirring and Final Electromagnetic Stirring

Based on Eulerian–Eulerian method, a 3D/2D multiphase solidification model, which takes into consideration the heat transfer and fluid flow with grains nucleation and crystal growth, is developed to predict the macrostructure evolution and macrosegregation in continuously cast round bloom. The results show that the mold electromagnetic stirring (M‐EMS) can accelerate superheat dissipation and promote grain nucleation, but the horizontal swirl induced by M‐EMS has a strong washing effect on the solidification front and leads to subsurface negative segregation. When the M‐EMS current intensity increases from 200 to 300 A, the subsurface negative segregation ratio decreases from 0.935 to 0.875. The final electromagnetic stirring (F‐EMS) not only improves the center segregation, but also leads to the formation of negative segregation zone near the round bloom center due to the enhancement of solute washing induced by F‐EMS. As the F‐EMS current intensity increases from 150 to 300 A, the center segregation ratio decreases from 1.148 to 1.075, and the negative segregation ratio near the strand center decreases from 0.985 to 0.977. Another phenomenon is found that the nucleation of equiaxed grain ahead of columnar tips restrains the solute diffusion and leads to a local macrosegregation in columnar‐to‐equiaxed transition zone.

Effect of Final Electromagnetic Stirring on Internal Thermal Stress, Strain and Cracking of Continuous Casting Bloom

Effect of Final Electromagnetic Stirring on Internal Thermal Stress, Strain and Cracking of Continuous Casting Bloom

Numerical Simulation of the Effect of Solidified Shell Conductivity and Billet Sizes on the Magnetic Field with Final Electromagnetic Stirring in Continuous Casting.

Coupled with the results of a 2D heat transfer model, a 3D electromagnetic stirring round billet model is developed, which is considered for the difference in the conductivity of solidified shell and molten steel. The electromagnetic field distribution features of the billet and the effect of round billet sizes on the electromagnetic field are investigated. It is found that as the solidified shell conductivity of the Φ600 mm round billet increases from 7.14 × 105 S·m-1 to 1.0 × 106 S·m-1, the magnetic induction intensity decreases and the maximum value of electromagnetic force drops from 7976.26 N·m-3 to 5745.32 N·m-3. The magnetic induction intensity on the center axis of the stirrer rarely changes in the range of Φ100-Φ200 mm. With the increase in the round billet from Φ300 mm to Φ600 mm, the magnetic induction intensity and the electromagnetic force on the center axis of the stirrer decrease slowly and then significantly. In the range of 2-8 Hz, as the current strength reaches its maximum, the electromagnetic force can be increased by increasing the current frequency for round billets of Φ100-Φ500 mm, while there is an optimal current frequency for round billets larger than Φ600 mm.

Digital-Twin-Based Coordinated Optimal Control for Steel Continuous Casting Process

A digital-twin-model-based optimal control system is presented for the steel continuous casting process. The system is designed for the coordinated optimization and dynamic control of secondary cooling and final electromagnetic stirring (FEMS), and involves three related parts. Firstly, a three dimensional real-time heat transfer model is established as the digital twin of the heat transfer process of continuous casting; for high accuracy, it is calibrated offline and calibrated online using measurements of the surface temperatures and shell thicknesses (only offline). Secondly, according to metallurgical rules, cooling and stirring are optimized coordinatively, based on the established digital-twin model and chaos particle swarm optimization algorithm. Thirdly, cooling and stirring are further dynamically controlled for quality stability. Finally, the system is applied in a bloom caster with model errors ≤ ±10 °C and control errors ≤ ±4 °C, which reduces the macro-segregation over grade 1.5 from 11% to 3.3%.

Numerical simulation of coupled fluid flow and solidification in a curved round bloom continuous caster with a combined rotary electromagnetic stirring

ABSTRACT The magnetically driven fluid flow and solidification process in a curved round bloom continuous caster for production of a highstrength low-alloy steel grade (Q345) with the diameter of ø600mm by a combined rotary electromagnetic stirring including the mold, the strand and the final electromagnetic stirring (M+S+F-EMS) is numerically described. The strand surface temperature and the solidified shell thickness are compared and validated by the available measured data. The magnetic field, fluid flow, temperature field and macrosolidification behaviors under the combined electromagnetic stirring are analyzed. The effects of casting speed and the position of the FEMS on the solidification and electromagnetic stirring are focused. Results show that the variation of casting speed is very important to control the length of liquid core and the solidification pool thickness for a large-size round bloom. The pool thickness and liquid fraction of the melt determines the range of the optimum stirring location and the effectiveness of the final electromagnetic stirring.

Effect of different positions of final electromagnetic stirring for ϕ800mm vertical round billet on fluid flow and heat transfer

Effect of different positions of final electromagnetic stirring for ϕ800mm vertical round billet on fluid flow and heat transfer

Effect of Final Electromagnetic Stirring on Flow, Solidification, and Solute Transport in Continuous Casting Bloom

Effect of Final Electromagnetic Stirring on Flow, Solidification, and Solute Transport in Continuous Casting Bloom

Effect of Mold Electromagnetic Stirring and Final Electromagnetic Stirring on the Solidification Structure and Macrosegregation in Bloom Continuous Casting

The solidification structure and macrosegregation are investigated in different current intensities of mold electromagnetic stirring (M‐EMS) and final electromagnetic stirring (F‐EMS) by a series of industrial trials during the 20CrMnTi bloom continuous casting (CC) process. With the current intensity of M‐EMS increasing from 100 to 390 A, the deflection angle of columnar dendrites increases from 25.0 to 32.49 deg. With the current intensity of M‐EMS increasing from 0 to 390 A, the equiaxed crystal ratio increases from 20.4% to 25.7% and center porosity varies little. With the increasing current intensity of M‐EMS, the negative segregation in the subsurface and positive segregation in the columnar‐to‐equiaxed transition (CET) zone deteriorate gradually. The M‐EMS has little effect on the center‐positive segregation, and the center‐positive segregation is maintained at 1.37–1.40. With the current intensity of F‐EMS increasing from 0 to 500 A, the equiaxed crystal ratio is within 25.3–25.8%, and the large center porosities disappear instead of numerous fine spots in the equiaxed zone. The degree of center‐positive segregation decreases from 1.48 to 1.30. For the CC process, to obtain a better internal quality of 20CrMnTi bloom, the optimal current intensities of M‐EMS and F‐EMS are 0 and 500 A, respectively.

Numerical simulation of macrosegregation in continuously cast gear steel 20CrMnTi with final electromagnetic stirring

A 3D/2D hybrid multi-physical-field mathematical model, which takes into consideration the thermosolutal buoyance, was developed to predict the macrosegregation of gear steel 20CrMnTi continuously cast by a curved billet caster with size of 160 mm × 160 mm, and investigated the effect of final electromagnetic stirring (F-EMS) on the fluid flow, heat transfer and solute distribution in the liquid core of continuously cast steel. The results show that the application of F-EMS eliminates the effect of thermosolutal buoyancy on the asymmetric distribution of carbon concentration in the cross section of billet and accelerates the final solidification of resident molten steel in the liquid core of strand, but promotes the negative carbon segregation near the billet center. When the gear steel 20CrMnTi is cast at the temperature of 1803 K and speed of 1.7 m/min, the solidification end advances forward from 9.84 to 9.72 m, and center carbon segregation ratio of billet decreases from 1.24 to 1.17 with the increase in current density of F-EMS from 0 to 350 A.

Numerical Modeling of the Macrosegregation Improvement in Continuous Casting Blooms by Using F-EMS

A three-dimensional mathematic model based on segmentation that joins the electromagnetic field, melt flow, heat transfer, solidification and solute transport in the whole casting domain has been established to study the solute transport at the final stage of solidification in a bloom continuous casting process. The effects of the final electromagnetic stirring (F-EMS) positions on the macrosegregation degree of the as-cast bloom are compared and analyzed. The results show that the maximum carbon segregation degree, the ratio of the local carbon concentration to the initial carbon concentration, is reduced from 1.292 to 1.254 with the application of F-EMS. In addition, the position of F-EMS is also an important factor. The maximum carbon segregation degrees are 1.254, 1.237 and 1.269 when the installation location of F-EMS is 14 m, 16 m and 18 m away from the meniscus, respectively. The optimal center solid fraction is about 0.1 at the F-EMS center for this study.

Prediction of maximum carbon element content in continuous casting billets of 82B cord steel based on statistics of extreme values method

The research of carbon content along the casting direction of 82B cord steel billets is of great significance for improving the quality of cord products from subsequent processing. However, the traditional segregation and billets quality evaluation methods have certain limitations, such as sampling length and analysis area, which affect the accuracy of quality judgment. Thus, the statistics of extreme values (SEV) was introduced to predict the maximum value of carbon element content along the casting direction, which can quantitatively characterize the segregation degree. The size of the selected billet is 150 mm × 150 mm, and the sampling location is the centerline of the billet. The experiment was conducted by considering the effect of cooling intensity and casting speed on the maximum value of carbon element content. Firstly, the calculation results show that the SEV method can predict the maximum value of carbon element content along the casting direction of 82B cord steel, and the SEV method is proved to be effective by analyzing the carbon distribution and fluctuation in billets. To some extent, the SEV method can break the limitations of the sampling length and analysis area by predicting the maximum value of carbon element on a larger range of continuous casting billets with few samples. During the continuous casting process, the increase in cooling intensity makes the surface shrinking rate increase, which can slow down the flow of solute-enriched liquid to the center, and the center segregation can be reduced. On the other hand, the function area of the final electromagnetic stirring can be expanded with the increase in the casting speed, which can reduce the concentration of carbon element in the center of the billets and reduce the maximum value of carbon element content. It can provide a new theoretical reference for the quantitative calculation of carbon content in continuous casting billets and the quality evaluation of continuous casting billets.

Coordinated Optimal Control of Secondary Cooling and Final Electromagnetic Stirring for Continuous Casting Billets

Secondary cooling and final electromagnetic stirring (F-EMS) are both key technologies for continuous casting. These parameters are usually optimized and controlled separately which caused internal quality fluctuations in unsteady conditions. In this paper, a coordinated optimal control strategy based on a multiobjective particle swarm optimization (MOPSO) algorithm is proposed for the parameter optimization of secondary cooling and F-EMS, which is solved based on multiobjective particle swarm optimization (MOPSO) algorithm. The solidification and heat transfer model are developed for the computation of billet temperature and the solidification, and the adaptive grid method is used to improve the diversity and robustness of optimal solutions. The secondary cooling water and F-EMS’ stirring current are dynamically controlled based on the optimization results. The results of field trials showed that the maximum carbon segregation and other quality indexes of billets can be improved significantly.

Comparison and integration of final electromagnetic stirring and thermal soft reduction on continuous casting billet

Final electromagnetic stirring (F-EMS) and thermal soft reduction (TSR) are techniques that improve the inner quality of continuous casting billets, but they have rarely been applied simultaneously. The application effects of F-EMS and TSR were compared, and a process integrating F-EMS and TSR was adopted for a billet continuous caster. A heat transfer model was established to calculate the thermal behavior of 82A tire cord steel billet. The locations of F-EMS and TSR were determined, followed by conducting a series of plant trials, involving F-EMS alone, TSR alone, and the integrated process of F-EMS and TSR. The results showed that F-EMS or TSR could effectively improve the inner quality of the billet under their respective suitable working conditions. Moreover, F-EMS was found to be more helpful in terms of improving central segregation, while TSR tended to improve V-segregation, central porosity, and pipe. The integration of F-EMS and TSR allowed the advantages of each technique to be utilized, thereby better improving the inner quality. Among all the working conditions, 82A steel billet showed optimum inner quality when the current of F-EMS was 240 A and the cooling intensity of TSR was 2.2 m3 h−1. These findings demonstrate that the integration of F-EMS and TSR is promising for application on continuous casting billets.

Effect of Final Electromagnetic Stirring Parameters on Central Cross-Sectional Carbon Concentration Distribution of High-Carbon Square Billet

The effect of final electromagnetic stirring parameters, with current intensity increasing from 300 A to 400 A and frequency increasing from 4 Hz to 12 Hz, on the electromagnetic forces and carbon concentration distribution of the central cross section of a 70 steel square billet have been studied. Along the center line of the liquid core zone, current intensity of 400 A and frequency of 8 Hz achieve the maximum electromagnetic force at the position 48 mm away from the billet edge among the 10 groups of stirring parameters. Nevertheless, along diagonal of the liquid core zone, the electromagnetic force near the diagonal center is the greatest and the current intensity of 280 A and frequency of 12 Hz obtain the maximum electromagnetic force. The optimal final electromagnetic stirring (F-EMS) parameter to uniform the central cross-sectional carbon concentration and minimize the center carbon segregation of 70 steel billet was obtained with a current intensity of 280 A and frequency of 12 Hz. Under this stirring parameter, the area ratios of carbon concentrations of 0.66 wt%, 0.70 wt% and 0.74 wt% in the middle of the billet cross section reached 28.5%, 56.9% and 10.9%, respectively. Moreover, the carbon segregation indexes for all sampling points were in the range of 0.92–1.05.

Effect of final electromagnetic stirring on solidification microstructure of GCr15 bearing steel in simulated continuous casting

The effect of final electromagnetic stirring on the solidification structure, element segregation, and carbides of GCr15 bearing steel was investigated. The experiment of continuous casting of the steel was carried out by using a continuous casting physical simulation apparatus with the final electromagnetic stirring. The liquid core profile was revealed by the pour-out method during the solidification process. Eight ingots were produced under different electromagnetic stirring parameters for comparison. The results show that, at the final stage of solidification, intense electromagnetic stirring exacerbates the central carbon segregation, resulting in more serious precipitation of the primary carbides. It is also found that the carbides in the segregation area are dominantly M3C type, together with a small amount of M7C3-type and M3C2-type carbides. In this physical simulation model, the optimal stirring parameters to obtain a fine and homogeneous structure are the liquid pool width of 15 mm, current intensity of 150 A, and stirring frequency of 5 Hz.

Quality Control of High Carbon Steel for Steel Wires.

High-carbon steel wires used for bridge cables, tire reinforcement materials and cutting materials of silicon ingot for photovoltaic industry require an extremely fine diameter and high strength. Poor control of centerline segregation, inclusion and microstructure of high-carbon steel is detrimental to drawability and subsequent fatigue performance. Prof. Weiqing Chen’s group at the University of Science and Technology Beijing (USTB) has been investigating the quality control of high-carbon steel through a low-cost one-stage hot rolling process since 2000. This paper reviews the main research from this group. The laboratory-scale and industrial results are presented. Intensive secondary cooling, final electromagnetic stirring (F-EMS), final permanent magnetic stirring (F-PMS), and soft reduction are investigated and applied to control centerline segregation, and the application scope is also discussed. A combination of redesign of submerged entry nozzle (SEN) and refining slag, utilization of Al-free refractory and the addition of low-melting-point compounds is studied and applied effectively to control inclusions. Measurements and mechanisms to control network cementite, martensite, banded structure and undesired texture are investigated and discussed. Integration of the above research has achieved industrial application in more than 10 steelworks and was further extended to application in spring steel, welding wire steel and some other wire rods.

Numerical Simulation of Electromagnetic Field in Round Bloom Continuous Casting with Final Electromagnetic Stirring

A 3D mathematical model was developed to simulate the electromagnetic field in Φ600 mm round bloom continuous casting with final electromagnetic stirring (F-EMS), and the model was verified using measured data for the magnetic flux density in the stirrer centre. The distribution of electromagnetic force and the influence of current intensity and frequency were investigated. The results show that the Joule heat generated by F-EMS is very small and its influence on secondary cooling heat transfer in the stirring zone can be ignored. With an increase in current frequency, the electromagnetic force density at R/2 and R/3 of the Φ600 mm round bloom first increases and then decreases, reaching a maximum at 10 Hz.

On the Alternate Stirring Mode of F-EMS for Bloom Continuous Castings

Local solute transportation behaviors under different alternate stirring parameters of final electromagnetic stirring (F-EMS) and their influences on the internal quality of the as-cast bloom are compared and evaluated based on a developed coupled model of electromagnetism, heat, and solute transport. To this end, plant trials were conducted in Shaoguan Steel, China. Under the action of F-EMS, a negative segregation band in an ellipse shape is observed at the central area of strand cross section, where the minimum carbon segregation degree is decreased from 0.98 to 0.84 as the stirring duration increases from 15 to 35 seconds in the alternate stirring mode, while it is reduced to 0.805 in the continuous stirring mode. The white band and shrinkage cavity are simultaneously observed at strand center under the conditions of continuous stirring mode, and alternate stirring mode with a stirring period of 35 seconds because of the local over-sustaining melt rotation. In contrast, the V-shape porosity belt width and strand center segregation fluctuation range increase from 60 to 90 mm and from 0.12 to 0.30, respectively, as the stirring duration is reduced from 25 to 15 seconds in the alternate stirring mode because of the poor mixing of the local melt at the strand center.

Coordinating optimisation of F-EMS and soft reduction during bloom continuous casting process for special steel

ABSTRACTTo control the halfway cracks and shrinkage cavities during bloom continuous casting (CC) process, final electromagnetic stirring (F-EMS) and soft reduction techniques have been coordinately optimised. The halfway crack and shrinkage cavity can be successfully controlled by adopting the CC technique parameters described as follows: (1) casting speed is 0.62 m min-1, (2) secondary cooling water ratio is 0.2 L kg−1, (3) reduction amount is 18 mm; (4) reduction region ranges from 19.9 m (location of M3 roller) to 25.4 m (location of M9 roller) distance from meniscus; and (5) corresponding distributions of reduction amount for each roller are 1, 1, 2, 3, 4, 4, and 3 mm along the casting direction. As compared to origin scheme for bearing steel, the difference between the maximum and minimum segregation degrees at the strand centre can be reduced from 0.35 to 0.09 under the optimal case.