Effect of casting speed on solidification and inclusion motions in bloom mold caster under the influence of in-mold electromagnetic stirring

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

Herein, the effect of bifurcated submerged entry nozzle (SEN) port angles on transient flow, solidification, and inclusion behavior in a bloom caster mold with electromagnetic stirring (EMS) is investigated. A 3D numerical model is developed to simulate the process, including time‐varying electromagnetic field and Lagrangian inclusion tracking approach, by varying inclusion density and size. The inclusion is modeled to be entrapped in the solidified shell when primary dendrite arm spacing (PDAS) is greater than inclusion size. As compared to the case without use of EMS, the percentage of shell thickness at the strand outlet is seen to increase by 22.18%, 9.45%, 8.03%, 9.31%, and 13.40% for different port angle values of 0°, 15°, 20°, 25°, and 30°, respectively, with EMS. The results show that EMS significantly influences the flow behavior by generating the swirl flow pattern that hinders the movement of inclusion downward in the domain. The bifurcated SEN with 30° port angle (without EMS) is seen to reduce inclusion entrapment and hence enhance inclusion removal. The outcome of present research may provide useful insights for optimizing the parameters of bloom caster mold to improve product quality, reduce production costs, and increase overall efficiency.

Numerical simulation for EMS induced solidification and inclusion behavior in bloom caster CC mold with bifurcated SEN

PurposeThe purpose of this study is to explore how a time-varying electromagnetic stirring (EMS) affects the fluid flow and solidification behavior in a slab caster continuous casting mold. Further, the study of inclusion movements in the mold is carried out under the effect of a time-varying electromagnetic field.Design/methodology/approachA three-dimensional coupled numerical model of solidification and magnetohydrodynamics has been developed for slab caster mold to investigate the inclusions transport by discrete phase model with the use of user-defined functions. Enthalpy porosity and the Lagrangian approach are applied to analyze the behavior of solidification and inclusion.FindingsThe study shows that the magnetic field density distribution has a radial symmetry in relation to the stirrer’s center. As the EMS current intensity increases, the strength of the lower recirculation zone gradually decreases and nearly disappears at higher intensities. Additionally, the area of localized remelting zone expands in the solidification front with rising current intensity. The morphology of inclusions and EMS current intensity have a significant impact on the behavior and movement of inclusions within the molten steel.Practical implicationsBy using the model, one can optimize the EMS parameter to enhance the quality of steel casting through the elimination of impurities and by improving the microstructure of cast that mainly depend on solidification and flow patterns of molten steel.Originality/valueUntil now, the use of time-varying EMS in the slab caster mold to study solidification and inclusion behavior has not been explored.

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.

Effective control of intense turbulence is a crucial challenge for achieving steady production with ultra-high casting speed in thin slab continuous casting. In thin slab casting process, specially designed multi-port submerged entry nozzle (SEN) with four outlets is utilised to ensure an ample supply of molten steel, necessitating the selection and optimisation of suitable Electromagnetic Braking (EMBr) equipment for steel jet control. This study established a comprehensive three-dimensional model of a funnel-type mould, employing a combined experimental-numerical approach to validate and investigate the flow, heat transfer, solidification and electromagnetic behaviour in the mould. The steel grade studied in the simulation is Q235B, and its physical properties were calculated based on its composition with a temperature range of 1450–1826 K. To analyse the influence of high casting speed on the flow and solidification behaviour in the mould, three casting speeds were selected for the study, which were 6, 7 and 8 m/min. The results indicate that the novel Bowl EMBr significantly suppressed the penetration of steel jet and thus enhanced the thickness and uniformity of the solidified shell. As the casting speed increases from 6 to 8 m/min, the solidified shell thickness at the mould exit decreases from 7.91 to 5.94 mm, with the stagnant growth region approaching the mould exit. This highlights the requirement to correspondingly increase EMBr strength under ultra-high casting speed condition to avoid remelting of the shell and the risk of molten steel leakage. The coupled mathematical model established in this study provides guidance for optimising EMBr structures and casting speed under special multi-port SEN conditions, offering recommendations for the rational control of flow, heat transfer and solidification process in the mould.

In the present paper, the mathematical model of the flow field of the mould under the electromagnetic stirring (EMS) conditions is established and verified with high-temperature quantitative velocity measurement. Under the conditions of different casting speeds, argon gas flow rates, and immersion depths of the submerged entry nozzle (SEN), the simulation results are in quantitative agreement with the high-temperature measurement results. The flow velocities of molten steel show a central symmetric circulation on the mould surface under EMS due to the stronger electromagnetic force near the wide wall of the mould and the weaker electromagnetic force near the mould centre. With decreasing the casting speed and the immersion depth of SEN and increasing the argon gas flow rate, the flow field in the mould tends to form the single roll flow (SRF) pattern. With increasing the casting speed 20% and 40%, the measurement velocity of molten steel near 1/4 width is increased from −0.202 m/s to 0.111 m/s first and then to 0.276 m/s with the velocity towards the SEN as the positive value, and the flow pattern changes from SRF to unstable flow (UF) first and then to double roll flow (DRF). With increasing the argon gas flow rate by 100% and 200%, the flow pattern changes from DRF to UF first and then to SRF. With increasing the immersion depth by 10.7% and 21.4%, the flow pattern changes from UF to DRF.

A coupling model of the flow field, initial solidification, alternating magnetic field (AM-field) and movement of argon bubble in the mold was established by combining the k-ε turbulence model with solidification model, Discrete Phase Model (DPM), Volume of Fluid (VOF) model and magnetohydrodynamics model. The industrial measured magnetic flux density (MFD) is consistent with the calculated MFD at a 15 mm interval from the wide wall, which verifies the reliability of the magnetic field model calculation. As the electromagnetic stirring (EMS) current intensity (EMSCI) grows, the calculated velocity of molten steel at 1/4 of the width direction of the mold surface decreases, which coincides well with measurement results. In addition, as the EMSCI is increased, the upper roll flow weakens, the horizontal rotational flow increases. The thickness of the solidified shell in the lower part of the narrow wall is increased due to the decreased impact force of the molten steel on the solidified shell of the narrow wall caused by the upward movement of the circulating flow. The volume fraction of argon bubbles around the SEN further decreases, and the distribution of them becomes more dispersed. Based on the research results, the optimal EMSCI under the present operating conditions is recommended as 700 A.

Segregation behavior and precipitated phases of super-austenitic stainless steel influenced by electromagnetic stirring

In this paper, the rod deflection method was applied to quantitatively measure velocity near the mold surface at high temperatures and the k-ε model coupled with a discrete phase model (DPM) was adopted to simulate the flow field in the mold. The calculated results match very well with the measured results under all the present conditions. Under the conditions of the large mold width of 1800 mm, 1.1 m/min casting speed and 140 mm submerged entry nozzle (SEN) immersion depth, the velocity near the mold surface decreases with increasing the argon gas flow rate. When the argon gas flow rate is 6 L/min, the flow pattern is the double roll flow (DRF). When the argon gas flow rate is increased to 10 L/min and 14 L/min, the flow pattern is the single roll flow (SRF), and the risk of slag entrainment increases. With an argon gas flow rate of 10 L/min, and an immersion depth of 160 mm, the velocity near the mold surface sensitively increases with increasing the casting speed. When the casting speed is 1.1 m/min, an intermediate flow (IF) is formed with the intensified mold surface fluctuation, which can easily result in slag entrainment defects. When the casting speed is only increased to 1.2 m/min, the velocity near the mold surface changes drastically and is close to the upper limit velocity of 0.4 m/s. When the casting speed is 1.1 m/min, and the argon gas flow rate is 10 L/min, the velocity near the mold surface is obviously increased with increasing the immersion depth. When the immersion depth of the nozzle increases from 140 mm and 160 mm to 180 mm, the flow pattern changes from SRF or IF to DRF. When the bottom shape of the SEN changes from mountain to well, the velocity near the mold surface decreases. We suggest adopting the well-bottom nozzle to reduce the risk of slag entrainment.

Numerical and experimental investigation of thermo-fluid flow and element transport in electromagnetic stirring enhanced wire feed laser beam welding

The structure of the turbulent flow in a slab mold is studied using a water model, various experimental techniques, and mathematical simulations. The meniscus stability depends on the turbulence structure of the flow in the mold; mathematical simulations using the k-e model and the Reynolds-stress model (RSM) indicate that the latter is better at predicting the meniscus profile for a given casting speed. Reynolds stresses and flow vorticity measured through the particle-image velocimetry (PIV) technique are very close to those predicted by the RSM model, and maximum and minimum values across the jet diameter are reported. The backflow in the upper side of the submerged entry nozzle (SEN) port (for a fixed SEN design) depends on the casting speed and disappears, increasing this process parameter. At low casting speeds, the jet does not report enough dissipation of energy, so the upper flow roll is able to reach the SEN port. At high casting speeds, the jet energy is strongly dissipated inside the SEN port, the narrow wall, and in the mold corner, weakening the momentum transfer of the upper flow roll, which is unable to reach the SEN port. At low casting speeds, meniscus instability is observed very close to the SEN, while at high casting speeds, this instability is observed in the mold corner. An optimum casting speed is reported where complete meniscus stability was observed. The flow structure at the free surface indicates a composite structure of islands with large gradients of velocity at high casting speeds. These velocity gradients are responsible for the meniscus instability.

A few reports have been made on the influence of electromagnetic stirring on weld zone, from the point of minimization of crystal grain and acceleration of blowhole decrease, in the case of TIG and MIG welding for titanium alloy or aluminium alloy.But the application for Submerged-arc welding has not been experimented. Therefore, in the former report, the authors investigated, how the electromagnetic stirring made influence on its bead shape, penetration and solidification structure of D.C.submerged-arc welding of mild steel. From this study the authors made it clear that the shape of penetration showed very peculiar change and that the primary crystals of weld metal were minimized.In this cotinuous report, the authors investigted how electromagnetic stirring hardness distribution and notch toughness of Submerge-arcd weld zone changed.The authors measured the hardness distribution by micro-Vickers Hardness tester, and the notch toughness by V-notch Charpy impact test. From these studies the authors have found out the following results.1) The hardness increases by electromagnetic stirring.2) As to the notch toughness, the authors made the transition curves of absorbed energy and fracture phase from the impact test, and from them, obtained the transition temperature of both 15ft-lb and fracture phase.As the result it became clear that both of the transition temperatures moved to the lower temperature side by 20 degrees C. The author also made the micro observation of fracture phases of impact test pieces with electron microscope and considered the changes of shape of the destructive phase caused by electromagentic stirring.

To increase the casting speed of φ150 mm round billets, a 3D mathematical model is established to investigate the effects of casting speed, mold parameters, and electromagnetic stirring (M‐EMS) on molten steel flow and heat transfer. The results indicate that higher casting speeds deepen the impingement zone and enlarge the high‐temperature region, leading to thinner shells and higher surface temperatures. When casting speed rises from 2.2 to 2.6 m min −1 , mold level fluctuation amplitude increases from 0.652 to 2.013 mm, and surface flow velocity rises from 0.0247 to 0.0293 m s −1 . Using a submerged entry nozzle (SEN) with a 25 mm diameter shifts the high‐temperature zone upward, accelerates superheat dissipation, and enhances heat transfer to the mold wall. The velocity distribution of molten steel near the solidification front correlates positively with shell growth in the M‐EMS zone. Both shell uniformity and remelting index decrease with increasing current intensity of M‐EMS. Industrial trials on 20# steel show that center porosity and segregation are controlled at grade 0.5 or below. When the superheat exceeds 25 °C, the proportion of billets with center shrinkage cavities below grade 0.5 decreases from 84.62% to 65%, while the occurrence of core defects increases significantly.

The melt flow, level fluctuation, temperature field, and solidification behavior coupled with electromagnetic stirring (EMS) effects in the continuous casting mold region of U71Mn steel bloom were numerically analyzed by commercial computational fluid dynamics (CFD) software named ANSYS FLUENT. The effects of submerged entry nozzle (SEN) structures and the installation methods for optimized four-port SEN on the flow pattern, level fluctuation, heat transfer and initial solidification behavior in a bloom mold loaded with EMS were investigated. The aim is to propose a better SEN condition for the big bloom casting of high railway steel. The water simulation experiments were conducted to show the flow characteristics under different SEN conditions and verify the numerical model of flow pattern. The experimental and numerical simulation results showed that the optimized four-port SEN with diagonal installation cannot only improve the flow pattern of the molten steel by alleviating the level fluctuation and reducing the impact pressure to the wall. It is also beneficial for temperature variation at both bloom surface and corner, as well as the local solidified shell thinning phenomena due to the elimination of impingement effect.