Mold Electromagnetic Stirring Research Articles

Evaluation of Mold Electromagnetic Stirring in Slab Continuous Casting Based on the Steel/Slag Interface Behavior

Evaluation of Mold Electromagnetic Stirring in Slab Continuous Casting Based on the Steel/Slag Interface Behavior

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.

Numerical investigation of solidification behavior and inclusion transport with M-EMS in continuous casting mold

The present study deals with the development of a multiphase numerical model of the continuous casting process of steel bloom. Two SEN configurations that differ in port angles are considered for the study of flow pattern, temperature distribution, solidification thickness, interface fluctuation and inclusion behavior during the process. The influence of mold electromagnetic stirring (M-EMS) on the various output parameters is examined. The results show that the upper circulation loop formed in the 15° port angle case is responsible for higher inclusion removal, high interface level, and low solidification thickness in the meniscus region compared to that of the 30° case. The presence of M-EMS completely changes the flow pattern below SEN. Strong rotational flow coupled with oppositely directed swirl flow provides high tangential velocity near the solidification front and high axial velocity in the core region. It results in fluctuation in shell thickness along the casting direction and decreasing the superheated steam penetration. However, flow patterns remain unaffected above the SEN as upwards swirl flow is not able to reach this region. On applying the M-EMS, inclusion entrapment in solidifying shell increases for both 15° and 30° cases. In contrast, inclusion removal at the interface decreases for 15° case and increases for 30° case.

Effect of Mold Electromagnetic Stirring on Metallurgical Behavior in Ultrahigh Speed Continuous Casting Billet Mold

A three‐dimensional model of fluid flow, heat transfer, solidification, and inclusion motion in billet mold at ultrahigh casting speed under electromagnetic field is developed. The low Reynolds number k–ε model coupled with electromagnetic model and Lagrangian discrete phase model is used to investigate the flow field, temperature field, solidification, and inclusions transport under different current intensities. The results show that mold electromagnetic stirring (M‐EMS) significantly alters the flow pattern of molten steel. The impact depth of the molten steel decreases as the stirring current intensity increases, and the horizontal swirl intensities of the molten steel increase with the stirring current intensity. As the current intensity increases from 500 to 700 A, the impact depth decreases from 0.637 to 0.575 m and the maximum tangential velocity increases from 0.477 to 0.898 m s−1. When the stirring current is intense, the flow of molten steel near the mold exit is reversed, and the molten steel flows asymmetrically and unsteadily. The M‐EMS effectively improves the transverse heat transfer of the molten steel in the mold, contributing to the dissipation of the molten steel superheat and the growth of the solidified shell. In addition, the removal ratio of the inclusions is improved significantly.

Effect of Nozzle Position on Fluid Flow and Solidification in a Billet Curved Mould using Mould Electromagnetic Stirring

Owing to the smaller cross‐sectional size of the billet, the effect of the position of the submerged entry nozzle (SEN) on the fluid flow in a curved mold is more prominent. The transient fluid flow, heat transfer, and solidification behavior at different nozzle positions and mold electromagnetic stirring (M‐EMS) are investigated using a 3D transient mathematical model. The symmetry index, S, is introduced to quantitatively evaluate the symmetry of the flow field. When the SEN is offset to the outer curve, S is the highest, the flow field mixing is the best, and the liquid level fluctuation is minimal. When the SEN is offset to the inner curve, S is the lowest, and the washing of the solidified shell on the inner curve side is more significant, causing the solidified shell thickness on the inner curve to be thinner, which can easily cause steel breakout accidents. The M‐EMS can improve the uneven flow field caused by the nozzle position. In actual production, the SEN can be appropriately offset to the outer curve, and the application of M‐EMS can improve the flow field distribution of molten steel.

Study on the metallurgical function of mold electromagnetic stirring in continuous casting bloom

The metallurgical function of mold electromagnetic stirring(M-EMS) was investigated by simulation according to the following factors: flow field, temperature field, solidification, removal of inclusions, slag entrainment, and macrosegregation. When the current intensity increased from 0 A to 490 A, the rotational flow induced by M-EMS enhanced gradually, and the impinging effect of jet flow on the solidification front decreased obviously. The average speed on the top surface increased from 0.015 m/s to 0.038 m/s. The temperature of the molten steel was more uniform, and the temperature on the top surface decreased from 1788.5 K to 1785.9 K. The depth of depressions induced by the jet flow decreased from 6.1 mm to 0.7 mm. When the current intensity of M-EMS was 390 A, the removal fraction of inclusions was the highest. When the current intensity of M-EMS was 0 A, no slag entrainment occurred. With the current intensity of M-EMS increasing from 290 A to 490 A, the net slag entrainment rate was 0.003, 0.013, and 0.047 kg/s. When the current intensity of M-EMS increased from 0 A to 490 A, the minimum carbon content of negative segregation in the subsurface of the bloom worsened from 0.176% to 0.167%. For the bloom CC process, the M-EMS scheme should be weak or no M-EMS to decrease the occurrence of slag entrainment and improve the negative segregation in the subsurface of the bloom.

Effect of the current intensity and positions of mold electromagnetic stirring on the macrosegregation in the full-length curved continuous casting bloom

A full-length curved continuous casting bloom mathematical model, coupling flow field, heat transfer, solidification, and electromagnetic stirring, was established to investigate the effect of the current intensity and positions of mold electromagnetic stirring (M-EMS) on the macrosegregation. M-EMS can optimize the negative segregation in the subsurface of the bloom and the positive segregation in the bloom center. With the current intensity of M-EMS increasing from 0 A to 350 A, the minimum carbon content in the subsurface of the bloom was 0.165%, 0.169%, 0.176%, and 0.182%. The carbon content in the bloom center was 0.246%, 0.243%, 0.241%, and 0.238%. The installation position of M-EMS can change the flow field and then affected the macrosegregation. When the positions of M-EMS were 0.77 m, 0.57 m, and 0.37 m beneath the meniscus, the minimum carbon content of negative segregation in the subsurface of the bloom was 0.174%, 0.182%, and 0.175%. The carbon content in the bloom center was 0.245%, 0.238%, and 0.235% respectively.

Behavior of Mold Electromagnetic Stirring for Round Bloom Castings and Its Eccentric Stirring Problem.

In this paper, a mold electromagnetic stirring (M-EMS) model was established to investigate the behavior of M-EMS for round bloom castings under different conditions, and an electromagnetic-flow-heat transfer-solidification coupling model was established to explore the problem of eccentric stirring for various formats of round blooms. The results show that the magnetic flux density decreased with the increase in the current frequency, but the electromagnetic torque increases first and then decreases with it, and the same structure of M-EMS for round blooms has the same optimal current frequency at any current intensity. The electromagnetic torque and electromagnetic force both increase as a quadratic function of the current intensity, and the electromagnetic torque, which drives the steel flow, can directly characterize the real M-EMS performance. The mold copper tube has a significant magnetic shielding effect on M-EMS, the stirring intensity decreases rapidly as the tube thickness increases, and the optimal stirring frequency decreases as well. In fact, the deviation between the stirrer center and the geometric center of the strand can result in the eccentric stirring phenomenon. When blooms with a section size of Φ350 mm are produced by Φ650 mm SMS-Concast casting machine, the upper region of the inner arc side and the lower region of the outer arc side are subject to a stronger washing effect, which makes the temperature of the inner and outer arcs show alternating differences. The jet flow from the five-port nozzle can suppress the difference in initial solidification symmetry between the inner and outer arcs of round blooms caused by eccentric stirring. This paper reveals the magnetic shielding effect of the mold copper tube and the magnetic field loss of the air between the stirrer and the inner and outer arcs of the copper, which lead to the stirring intensity and the eccentric stirring phenomenon.

Effect of Swirling Flow Nozzle on Fluid Flow and Solidification in a Round Bloom Continuous Casting Mold

The nozzle structure has an important effect on the fluid flow in the mold, which can significantly improve the solidified shell and product quality of alloy steel round bloom. The transient fluid flow, heat transfer, and solidification behavior under different nozzle structures and mold electromagnetic stirring (M-EMS) are investigated using a 3D transient mathematical model. The results show that a third small recirculation zone appears near the meniscus after the application of the swirling flow nozzle (SFN). The impact depth of SFN is shallower than that of the original submerged entry nozzle (SEN) impact, and the lower circulation zone is shifted upward. The horizontal swirling flow generated by SFN can significantly weaken the washing of the initial shell by high-temperature steel and improve the uneven growth phenomenon of the inner and outer curved solidified shell caused by mold curvature. The swirling flow produced by M-EMS in the mold can also improve the washing of the initial shell by the high-temperature jet and the uneven growth of the inner and outer curved shell. M-EMS can expand the high-temperature zone in the upper part of the mold, promote the superheat dissipation of the molten steel, and promote the growth of the solidified shell. In addition, after the application of M-EMS, the tangential velocity of -15° SFN in the meniscus is smaller, and the resulting liquid level fluctuation is lower at 5.07 mm, which is less likely to produce slag entrapment and is conducive to improving the quality of round bloom.

The Investigation of Phase Transition and Solute Transport for Bloom Continuous Casting with Steel Strip‐Feeding Process and Mold Electromagnetic Stirring: A Comparative Study

Based on the finite volume method, a continuum model that coupled enthalpy‐porosity approach is developed herein to investigate the fluid flow, phase transition, and macrosegregation in the solidification process for bloom continuous casting. The optimal parameters of the process of feeding strip technology (FST) are obtained, and the effects of different processes of regular continuous casting, mold electromagnetic stirring (M‐EMS), and FST on the superheat degree and macrosegregation are compared. The results show that the process of FST can not only greatly reduce the superheat degree of liquid steel and improve the macrosegregation in the bloom center, but also effectively avoid the deterioration of negative segregation defects at the edge of bloom, compared with the processes of regular continuous casting and M‐EMS. The best process parameters for the process of FST are as follows: the strip feeding position is 0.12 m far away from the bloom centerline, and the steel strip feeding velocity is 0.20 m s−1.

The Role of Mold Electromagnetic Stirring in the Dissipation of Superheat during the Continuous Casting of Billets

A two‐phase solidification model coupling mold electromagnetic stirring (M‐EMS) is used to investigate the initial solidification in the mold region of billet continuous casting. One novelty of this numerical study is to quantify how the M‐EMS induces primary and secondary flows, interacting with the jet flows coming from the submerged entry nozzle, and how those flows further influence the dissipation of superheat and the initial solidification. The role of the M‐EMS in speeding up the superheat dissipation in the mold region, known from previous studies and casting practices, is quantitatively verified. Additionally, some new knowledge regarding the M‐EMS is found. The total heat transfer rate from the strand surface to the water‐cooled copper mold is not affected by the M‐EMS; with the M‐EMS, the superheat effect on the solid growth can only be detected in the out‐of‐the‐mold region, while the shell growth inside the mold region is quite independent of the superheat; a strong M‐EMS tends to accelerate the growth of the solid shell in the mold region, but delays its growth in the secondary cooling zones. The aforementioned new findings may only be valid for the case of the current billet casting, to be confirmed for other casting formats/parameters.

Effects of mold electromagnetic stirring on heat transfer, species transfer and solidification characteristics of continuous casting round billet

In this study, the temperature distribution, species transfer, and solidification behavior in round billet continuous casting with mold electromagnetic stirring (M-EMS) was numerically investigated. The joule heat induced by the M-EMS and the liquid fraction profiles in the mushy zone were observed, whereby it was found that increasing current intensity caused further increase in electromagnetic force, which reduced the impact depth of liquid steel while accelerating the dissipation of superheat. The high liquid fraction in the mushy zone at the exit of the secondary cooling zone were 68.1% (case 1) and 77.1% (case 6). The central carbon contents of the round billets were 0.337 wt% (case 1) and 0.335 wt% (case 6). Moreover, the proportion of solidification microstructure and secondary dendrite arm spacing of the round billet samples were compared, which revealed that increasing the current intensity, casting speed, and cooling intensity, were all conducive to improving the uniformity of carbon distribution and compactness of the solidification structure.

Measurement and Calculation of Magnetic Flux Density During Mold Electromagnetic Stirring on a Continuous Casting Bloom Mold

Measurement and Calculation of Magnetic Flux Density During Mold Electromagnetic Stirring on a Continuous Casting Bloom Mold

Numerical Simulation for Two‐Phase Flow, Heat Transfer, and Inclusion Transport in Bloom Mold Considering the Effects of Argon Gas Injection and Mold Electromagnetic Stirring

A mathematical model based on the Eulerian–Eulerian–Lagrangian method is developed to investigate the two‐phase flow, temperature distribution, and inclusion transport, considering the effect of argon gas injection (AGI) and mold electromagnetic stirring (M‐EMS) in the bloom mold. The magnetic resistance force is adopted to account for the effect of the magnetic field on bubbles. It is demonstrated in the results that when AGI is applied, plumes form near the submerged entry nozzle (SEN) and increase the velocity in the upper part of the mold. While M‐EMS is applied, the swirl flow significantly increases the overall flow velocity and superheat dissipation. In addition, AGI and M‐EMS increase the fluctuation and temperature of the free surface, lower the peak heat flow, and promote inclusions removal. When AGI is applied with M‐EMS, the swirl flow and plumes in the upper part of the mold are weakened due to the interaction between them, and the level fluctuation is lower than that of applying AGI or M‐EMS separately. The heat flow and free surface temperature are more uniform, and the inclusion removal rate further increases. Meanwhile, M‐EMS drives bubble columns to the location between the two ports of SEN and gathers bubbles around the SEN.

Modeling of the as-cast structure and macrosegregation in the continuous casting of a steel billet: Effect of M-EMS

Mold electromagnetic stirring (M-EMS) has been introduced into the continuous casting of steel billets to promote the formation of a central equiaxed zone; however, the formation mechanism of the equiaxed crystals and the effect of M-EMS on crystal transport are not fully understood. Currently, a three-phase volume average model was used to study the solidification in a billet continuous casting (195 mm × 195 mm). The modeling results showed that the main function of M-EMS in this type of billet casting is to promote superheat dissipation in the mold region, leaving the liquid core out of the mold region undercooled. Although both, heterogeneous nucleation and crystal fragmentation, are considered to be the origins of equiaxed crystals, M-EMS appeared to impact crystal fragmentation more effectively. A small portion of equiaxed crystals could be brought by the M-EMS induced swirling flow into the superheated zone (upper mold region) and remelted; most equiaxed crystals settled in the lower undercooled zone, where they continued to grow and form a central equiaxed zone. These simultaneous phenomena represent an important species/energy transport mechanism, influencing the as-cast structure and macrosegregation. Negative segregation occurred in the central equiaxed zone, positive segregation occurred at the border of the columnar zone, and a trail of negative segregation occurred in the subsurface region of the billet. Finally, parameter studies were performed, and it was found that the shielding effect of the copper mold, electrical isolation at the strand-mold interface, and relatively high electrical conductivity of the strand shell affect the M-EMS efficiency.

Effect of Mold Electromagnetic Stirring on the Flow and Solidification of Φ 800 mm Round Blooms

Knowing the effect of electromagnetic force on fluid flow and solidification within the molds of large-size round blooms is of paramount importance to minimize internal and external defects. In this regard, a three-dimensional coupling model is established, containing magnetohydrodynamics, fluid flow, and heat transfer within the mold, and a new approach for the uniformity of the initial shell is presented. Meanwhile, the effect of stirring parameters on fluid flow and solidification is discussed. The results show that M-EMS can significantly change the temperature and velocity distribution within the mold. These changes can stabilize the level fluctuations and make the initial shell uniform. The maximum industrial height fluctuation was reduced from 1.9 mm to 1.3 mm when the stirring intensity was 375 A/3 Hz. The stirring intensity of M-EMS is relatively ideal.

Numerical Simulation of the Fluid Flow, Heat Transfer, and Solidification in Ultrahigh Speed Continuous Casting Billet Mold

Ultrahigh‐speed casting is the most remarkable feature of billet high‐efficiency continuous casting. The transient fluid flow, heat transfer, and solidification behavior under different casting speeds, submerged entry nozzle (SEN) parameters, and mold electromagnetic stirring (M‐EMS) are investigated using a 3D transient mathematical model. The results show that a typical roll flow pattern is generated for all casting speeds, while a third small recirculation zone developed near the solidified shell at the casting speed of 6.0 m min−1. When the casting speed increases, the impact depth of the molten steel increases from 0.748 to 0.844 m, the velocity and level fluctuation at the steel/slag interface increases, the high‐temperature zone moves downward, and the shell thickness is reduced from 16.2 to 11.1 mm. As the SEN inner diameter and immersion depth increases, the impact depth increases, the velocity and level fluctuation at the steel/slag interface decreases, and the shell thickness at the mold exit is ≈11.0 mm. When the SEN immersion depth and inner diameter are 120 and 40 mm, respectively, the flow and temperature fields in the mold are the most appropriate. In addition, the M‐EMS have a great effect on the fluid flow and heat transfer behavior.

Effect of mold electromagnetic stirring on solidification structure and solute segregation in continuous casting bloom

Effect of mold electromagnetic stirring on solidification structure and solute segregation in continuous casting bloom

Numerical investigation into flow and solidification behavior of billet continuous casting with and without mold electromagnetic stirring

AbstractMold electromagnetic stirring (M‐EMS) in the continuous casting process improves the metallurgical quality of the caster as it acts as a dendrite breaker and increases the heat transfer. In this study, a numerical model of molten steel flow and solidification of continuous casting billet caster is developed. Further, this model is coupled with M‐EMS to investigate the influence of stirring on molten steel flow dynamics and solidification in the mold. The magnetic field calculations are performed in ANSYS Maxwell and computational fluid dynamics solver Fluent is used for flow field and heat transfer calculations. The fluid flow, temperature field, and solidification are investigated and compared with without M‐EMS case. The results indicate that the application of M‐EMS significantly changes flow dynamics in the mold. Strong swirl flow is dominant and a significant increment in tangential velocity is observed in the presence of M‐EMS. High intense rotational flow about the strand center gives rise to the superheat transfer near the solidification front, which further enhances the temperature in this region and thereby decreases the solidification thickness in the M‐EMS‐affected zone

The simulation of mould metallurgical behaviour under electromagnetic stirring for vertical large bloom

ABSTRACT According to the mould electromagnetic stirring of vertical round billet continuous casting, a three-dimensional mathematical model of electromagnetic field was established to study the distribution of magnetic field in the mould. On the centre cross section of agitator, the distribution of magnetic flux density is small in the centre and large in the edge, in the centre longitudinal section, the maximum value of magnetic flux density at the lower edge of the mould. The influence of electromagnetic parameters on the flow field and temperature field in mould was studied. When the section of round billet is 800 mm, the current intensity is 380 A and the current frequency is 3 Hz, and the proportion of equiaxial crystal is up to 43.6%. The central shrinkage hole, central crack and central porosity are all less than grade 1, and there is no white band, the stirring intensity of M-EMS is relatively ideal.