Slag-metal Interface Research Articles

The Role of Submerged Entry Nozzle Port Shape on Fluid Flow Turbulence in a Slab Mold

The fluid flow of liquid steel in a wide slab mold (1880 × 230 mm) influenced by two different submerged entry nozzle (SEN) designs (bifurcated nozzles with rectangular, SEN-R, vs square, SEN-S, ports) and immersion depths of 115 and 185 mm was studied using a 1:1 scale water model. To analyze the fluid dynamics, particle image velocimetry and video recording techniques were used. The fluid-flow dynamics indicate that the discharging jets using either SEN design suffer strong wandering and raveling effects that enhance turbulence in the meniscus region. The preceding results show the existence of velocity spikes (defined as velocities with magnitudes that exceed the standard deviation of the average velocity) in the submeniscus region. Using the SEN-R ports yields more velocity spikes per minute with larger magnitudes than using the SEN-S, which could be the main cause of the detrimental quality of steel. The capability of slag entrainment by the flow developed by a nozzle was the criterion employed to evaluate quantitatively the merits of one nozzle over the other. This criterion is based on the capillary number, which gives the ratio between viscous-inertial and surface forces at the metal–slag interface.

Control of Slag-Dragging Effects at the Metal–Slag Interface through Electromagnetic Brake in a Slab Mold

AbstractTurbulent flow when steel is delivered through a nozzle in a slab mold induces dragging forces at the metal–slag interface that entrain slag droplets into the metal bulk. These dragging effects are discontinuous and correspond to the velocity fluctuations of turbulence at that interface which themselves, are dependent on nozzle immersion, nozzle design, mold width and casting speed. Slag viscosity and density, metal viscosity and slag layer thickness are employed to estimate that critical velocity which is embodied in a critical capillary number for some established mold operating conditions. This approach permits the link between all operating variables including flux chemistry and nozzle design with the interface instability. A relationship between the capillary number and the magnetic field strength used to brake the liquid steel is established which is used to assure the interface stability for any operating condition and flux chemistry.

Modeling Flow Turbulence in a Continuous Casting Slab Mold Comparing the use of Two Bifurcated Nozzles with Square and Circular Ports

Flow patterns of liquid steel in a thick slab mold, fed by bifurcated nozzles, are modeled through water modeling using characterization techniques such as particle image velocimetry (PIV), ultrasound velocimetry probe (UPV), and mathematical simulations using the large eddy simulation (LES) model. Geometries of nozzle ports include circular and square shapes with similar cross-section area. Square ports deliver wandering jets that occupy about 66% of the port area, and are raveled during their pass through the mold impacting the narrow face. Circular ports deliver compact jets mainly through the lower edge occupying only about 45% of the port area. The analysis of the flow structures indicates that the circular ports form more turbulent jets than square ones for the same flow rate of liquid. Mathematical simulations, using the LES model, predict acceptably well measured velocity fields. Slag entrainment through mechanisms of shear-drag forces at the metal–slag interface is estimated through a critical capillary number which involves slag viscosity, interfacial tension, and fluid velocity. At deep nozzle immersions, this capillary model predicts more slag entrainment using the bifurcated nozzle with circular ports.

Numerical Simulation of the Interaction Between Supersonic Oxygen Jets and Molten Slag–Metal Bath in Steelmaking BOF Process

The impinging of multiple jets onto the molten bath in the BOF steelmaking process plays a crucial role in reactor performance but is not clearly understood. This paper presents a numerical study of the interaction between the multiple jets and slag–metal bath in a BOF by means of the three-phase volume of fluid model. The validity of the model is first examined by comparing the numerical results with experimental measurement of time-averaged cavity dimensions through a scaled-down water model. The calculated results are in reasonably good agreement with the experimental data. The mathematical model is then used to investigate the primary transport phenomena of the jets-bath interaction inside a 150-ton commercial BOF under steelmaking conditions. The numerical results show that the cavity profile and interface of slag/metal/gas remain unstable as a result of the propagation of surface waves, which, likely as a major factor, governs the generation of metal droplets and their initial spatiotemporal distribution. The total momentum transferred from the jets into the bath is consumed about a half to drive the movement of slag, rather than fully converted as the stirring power for the metal bath. Finally, the effects of operational conditions and fluid properties are quantified. It is shown that compared to viscosity and surface tension of the melts, operating pressure and lance height have a much more significant impact on the slag–metal interface behavior and cavity shape as well as the fluid dynamics in the molten bath.

Dynamic Modeling of LD Converter Steelmaking: Reaction Modeling Using Gibbs’ Free Energy Minimization

Slag–metal emulsion plays an important role in the oxidation kinetics of metalloids in oxygen steelmaking. The importance of droplet generation rate, droplet size, and its residence time in the slag–metal emulsion on the overall reaction kinetics has become evident in recent times. Residence times of the droplets are strongly dependent on the decarburization rate, the CO bubbles giving a buoyant force to the droplets. The present work aims at developing a mathematical model for predicting the composition evolutions of the slag and the metal phases as the blow proceeds in an LD converter. The process dynamics are modeled by dividing the LD convertor into three separate continuous stirred tank reactors. Oxidation reactions are assumed to be primarily taking place at the interface between the slag and the metal phases in the emulsion. Among the different mass transfer and reaction steps controlling the kinetics, the mass transfer of FeO in the slag phase and that of the metalloids within the metal droplet are assumed to be rate-controlling. For a Fe-C-X (X = Mn, Si etc.) droplet, simultaneous removal of elements have been modeled by Gibbs’ free energy minimization at the slag–metal interface. Effects of droplet size, mass transfer coefficient, and initial carbon content on the mean residence time of metal droplets in the slag–metal emulsion have also been identified. Mixing in the metal phase is simulated in terms of metal exchange rate and the reactor weight ratio between the upper and the lower parts of the bath.

Unsteady Fluctuation Behavior of Slag-Metal Interface in a Slab Continuous Casting Mold

Unsteady Fluctuation Behavior of Slag-Metal Interface in a Slab Continuous Casting Mold

Effect of Slag on Inclusions During Electroslag Remelting Process of Die Steel

Many factors influence the non-metallic inclusions in electroslag steel including furnace atmosphere and inclusions’ content in the consumable electrode, slag amount and its composition, power input, melting rate, filling ratio, and so on. Fluoride containing slag, which influences the non-metallic inclusions to a great extent, has been widely used for the electroslag remelting process. The current paper focuses on the effect of fluoride containing slag on the inclusions in electroslag ingots based on the interaction of the slag-metal interface and electroslag remelting process. In this work, die steel of CR-5A and several slags have been employed for investigating the effect of slag on inclusions in an electrical resistance furnace under argon atmosphere in order to eliminate the effect of ambient oxygen. Specimens were taken at different times for analyzing the content, dimensions, and type of non-metallic inclusions. Results of quantitative metallographic analysis indicate that a multi-component slag has better capacity for controlling the amount of inclusions; especially protective gas atmosphere has also been adopted. The findings of inclusions in electroslag steel by SEM–EDS analysis reveal that most non-metallic inclusions in electroslag steel are MgO-Al2O3 inclusions for multi-component slags, but it is Al2O3 inclusions when remelting using conventional 70 wt pct CaF2-30 wt pct Al2O3 slag. The maximal inclusions’ size using multi-component slags is less than that using conventional binary slag. Small filling ratio as well as protective gas atmosphere is favorable for controlling the non-metallic inclusions in electroslag steel. All the results obtained will be compared to the original state inclusions in steel, which contribute to choice of slag for electroslag remelting.

Effect of Melting and Refining with DC-Arc on the Yield of Alloy Element

In order to know what effect on the yield of alloy elements will be if the steel is melted/refined with the DC arc furnace, the effect of melting and refining with DC-arc on the yield of alloy element has been investigated by a melting experiment, in which the melting/refining is switched to continuous melting/refining with DC-arc after the molten metal is contact with the molten slag for 41 minutes without DC-arc, and by a contrast experiment of melting/refining with DC-arc and with an AC-arc. When DC current passes through the slag-metal interface and the slag-gas interface, the existence of the electrolysis phenomenon during the DC-arc steel melting/refining has been confirmed. Electrolysis participates in the metallurgical reaction. The phenomenon of two or more electrode reactions taking place simultaneously at both the slag-metal interface and the slag-gas interface has also been observed. The two phenomena cause the accelerating loss of the alloy-elements in the molten metal and the decreasing of concentrations of the corresponding oxides in the molten slag. The electrochemical transfer of oxygen from the molten slag to the molten metal ((O2-)=[+2e and (O2-)=1/2O2+2e) at the slag-metal interface has been observed, and causes the increasing of oxygen content in the molten metal.

Numerical Simulations of Inclusion Behavior in Gas-Stirred Ladles

A computation fluid dynamics–population balance model (CFD–PBM) coupled model has been proposed to investigate the bubbly plume flow and inclusion behavior including growth, size distribution, and removal in gas-stirred ladles, and some new and important phenomena and mechanisms were presented. For the bubbly plume flow, a modified k-e model with extra source terms to account for the bubble-induced turbulence was adopted to model the turbulence, and the bubble turbulent dispersion force was taken into account to predict gas volume fraction distribution in the turbulent gas-stirred system. For inclusion behavior, the phenomena of inclusions turbulent random motion, bubbles wake, and slag eye forming on the molten steel surface were considered. In addition, the multiple mechanisms both that promote inclusion growth due to inclusion–inclusion collision caused by turbulent random motion, shear rate in turbulent eddy, and difference inclusion Stokes velocities, and the mechanisms that promote inclusion removal due to bubble-inclusion turbulence random collision, bubble-inclusion turbulent shear collision, bubble-inclusion buoyancy collision, inclusion own floatation near slag–metal interface, bubble wake capture, and wall adhesion were investigated. The importance of different mechanisms and total inclusion removal ratio under different conditions, and the distribution of inclusion number densities in ladle, were discussed and clarified. The results show that at a low gas flow rate, the inclusion growth is mainly attributed to both turbulent shear collision and Stokes collision, which is notably affected by the Stokes collision efficiency, and the inclusion removal is mainly attributed to the bubble-inclusion buoyancy collision and inclusion own floatation near slag–metal interface. At a higher gas flow rate, the inclusions appear as turbulence random motion in bubbly plume zone, and both the inclusion–inclusion and inclusion-bubble turbulent random collisions become important for inclusion growth and removal. With the increase of the gas flow rate, the total removal ratio increases, but when the gas flow rate exceeds 200 NL/min in 150-ton ladle, the total removal ration almost does not change. For the larger size inclusions, the number density in bubbly plume zone is less than that in the sidewall recirculation zones, but for the small size inclusions, the distribution of number density shows the opposite trend.

The Rate of the Phosphorous Reaction Between Liquid Iron and Slag

In the current study, the rates of dephosphorization and rephosphorization of liquid iron with simulated steelmaking slags were investigated at 1873 K (1600° C). The experiments were conducted in an induction furnace with supplemental heating to maintain a consistent temperature within both the metal and slag phases. An integrated form of the rate equation was used to evaluate the results, assuming mass transfer in both the slag and metal was rate controlling. The results of the current and previous studies indicate that the mass transfer parameter, the slag-metal surface area, and the overall mass transfer coefficient (A*k0), decreased as the reaction proceeded. It is proposed that initially when the rate and oxygen flux are high, the interfacial energy decreases, and the interfacial fluid velocity increases causing disruption of the slag metal interface. The consequent increases in interfacial area and interfacial fluid flow cause A*k0 to be high initially and then decrease as the oxygen flux decreases.

Modeling Related to Secondary Steel Making

AbstractA big number of publications were collected to provide an overall picture of the modeling in secondary steelmaking. The referred papers could illustrate the general and typical approaches in modeling the process and sub‐processes of steelmaking. The flow, mass transfer, and heat transfer in the reactors were briefly discussed. While modeling of slag–metal interface was summarized, the strong need for further understanding of the interface was emphasized. Modeling approaches of inclusion generation, growth, and separation were also discussed. The requirement of in‐depth knowledge of these phenomena was addressed. The present review intends not only to provide a literature survey, but also to remind the researchers the importance of keeping balance between the experimental and modeling studies.

Studies of dynamic mass transfer at the slag–metal interface – Interfacial velocity measurements

Abstract The dynamics of oxygen transport along the slag–metal interface of pure iron and alumina-saturated CaO–Al2O3–SiO2 slag was studied using high-temperature X-ray image analysis. The oscillations of the metal drop occurring due to the interfacial movement of oxygen atoms driven by Marangoni forces were studied in detail. The change in interfacial area during the oscillations was measured using a digitizing software and MATLAB. It was observed that the interfacial velocity as a function of oxygen exhibits insignificant variation with temperature. Further, the values obtained for the interfacial velocity using oxygen concentration difference at the interface were slightly lower in comparison to those using sulfur. The possible reason for this lower velocity could be that, although oxygen is a smaller atom compared to that of sulfur, the energy barrier at the free iron surface is higher for oxygen, thus hindering its motion along the interface.

A Sulfide Capacity Prediction Model of CaO-SiO2-MgO-FeO-MnO-Al2O3 Slags during the LF Refining Process Based on the Ion and Molecule Coexistence Theory

A sulfide capacity prediction model of CaO-SiO2-MgO-FeO-MnO-Al2O3 ladle furnace (LF) refining slags has been developed based on the ion and molecule coexistence theory (IMCT). The predicted sulfide capacity of the LF refining slags has better accuracy than the measured sulfide capacity of the slags at the middle and final stages during the LF refining process. Increasing slag binary basicity, optical basicity, and the Mannesmann index can lead to an increase of the predicted sulfide capacity for the LF refining slags as well as to an increase of the sulfur distribution ratio between the slags and molten steel at the middle and final stages during the LF refining process. The calculated equilibrium mole numbers, mass action concentrations of structural units or ion couples, rather than mass percentages of components, are recommended to represent the slag composition for correlating with the sulfide capacity of the slags. The developed sulfide capacity IMCT model can calculate not only the total sulfide capacity of the slags but also the respective sulfide capacity of free CaO, MgO, FeO, and MnO in the slags. The comprehensive contribution of the combined ion couples (Ca2+ + O2−) and (Mn2+ + O2−) on the desulfurization reactions accounts for 96.23 pct; meanwhile, the average contribution of the ion couple (Fe2+ + O2−) and (Mg2+ + O2−) only has a negligible contribution as 3.13 pct and 0.25 pct during the LF refining process, respectively. The oxygen activity of bulk molten steel in LF is controlled by the [Al]–[O] equilibrium, and the oxygen activity of molten steel at the slag–metal interface is controlled by the (FeO)–[O] equilibrium. The ratio of the oxygen activity of molten steel at the slag–metal interface to the oxygen activity of bulk molten steel will decrease from 37 to 5 at the initial stage, and further decrease from 28 to 4 at the middle stage, but will maintain at a reliable constant as 5 to 14 at the final stage during the LF refining process. The proposed high-oxygen potential layer of molten steel beneath the slag–metal interface can be quantitatively verified.

A Thermodynamic Model of Sulfur Distribution Ratio between CaO–SiO2–MgO–FeO–MnO–Al2O3 Slags and Molten Steel during LF Refining Process Based on the Ion and Molecule Coexistence Theory

A thermodynamic model for calculating the sulfur distribution ratio between ladle furnace (LF) refining slags and molten steel has been developed by coupling with a developed thermodynamic model for calculating the mass action concentrations of structural units in LF refining slags, i.e., CaO-SiO2-MgO-FeO-MnO-Al2O3 hexabasic slags, based on the ion and molecule coexistence theory (IMCT). The calculated mass action concentrations of structural units in CaO-SiO2-MgO-FeO-Al2O3-MnO slags equilibrated or reacted with molten steel show that the calculated equilibrium mole numbers or mass action concentrations of structural units or ion couples, rather than mass percentage of components, in the slags can represent their reaction abilities. The calculated total sulfur distribution ratio shows a reliable agreement with the measured or the calculated sulfur distribution ratio between the slags and molten steel by other models under the condition of choosing oxygen activity based on (FeO)-[O] equilibrium. Meanwhile, the developed thermodynamic model for calculating sulfur distribution ratio can quantitatively determine the respective contribution of free CaO, MgO, FeO, and MnO in the LF refining slags. A significant difference of desulfurization ability among free component as CaO, MgO, FeO, and MnO has been found with approximately 87-93 pct, 11.43-5.85 pct, 0.81-0.60 pct and 0.30-0.27 pct at both middle and final stages during LF refining process, respectively. A large difference of oxygen activity is found in molten steel at the slag-metal interface and in bulk molten steel. The oxygen activity in molten steel at the slag-metal interface is controlled by (FeO)-[O] equilibrium, whereas the oxygen activity in bulk molten steel is controlled by [Al]-[O] equilibrium. Decreasing the high-oxygen-activity boundary layer beneath the slag-metal interface can promote the desulfurization reaction rate effectively or shorten the refining period during the LF refining process.

A Thermodynamic Model of Phosphorus Distribution Ratio between CaO-SiO2-MgO-FeO-Fe2O3-MnO-Al2O3-P2O5 Slags and Molten Steel during a Top–Bottom Combined Blown Converter Steelmaking Process Based on the Ion and Molecule Coexistence Theory

A thermodynamic model for calculating the phosphorus distribution ratio between top–bottom combined blown converter steelmaking slags and molten steel has been developed by coupling with a developed thermodynamic model for calculating mass action concentrations of structural units in the slags, i.e., CaO-SiO2-MgO-FeO-Fe2O3-MnO-Al2O3-P2O5 slags, based on the ion and molecule coexistence theory (IMCT). Not only the total phosphorus distribution ratio but also the respective phosphorus distribution ratio among four basic oxides as components, i.e., CaO, MgO, FeO, and MnO, in the slags and molten steel can be predicted theoretically by the developed IMCT phosphorus distribution ratio prediction model after knowing the oxygen activity of molten steel at the slag–metal interface or the Fe t O activity in the slags and the related mass action concentrations of structural units or ion couples in the slags. The calculated mass action concentrations of structural units or ion couples in the slags equilibrated or reacted with molten steel show that the calculated equilibrium mole numbers or mass action concentrations of structural units or ion couples, rather than the mass percentage of components, can present the reaction ability of the components in the slags. The predicted total phosphorus distribution ratio by the developed IMCT model shows a reliable agreement with the measured phosphorus distribution ratio by using the calculated mass action concentrations of iron oxides as presentation of slag oxidation ability. Meanwhile, the developed thermodynamic model for calculating the phosphorus distribution ratio can determine quantitatively the respective dephosphorization contribution ratio of Fe t O, CaO + Fe t O, MgO + Fe t O, and MnO + Fe t O in the slags. A significant difference of dephosphorization ability among Fe t O, CaO + Fe t O, MgO + Fe t O, and MnO + Fe t O has been found as approximately 0.0 pct, 99.996 pct, 0.0 pct, and 0.0 pct during a combined blown converter steelmaking process, respectively. There is a great gradient of oxygen activity of molten steel at the slag–metal interface and in a metal bath when carbon content in a metal bath is larger than 0.036 pct. The phosphorus in molten steel beneath the slag–metal interface can be extracted effectively by the comprehensive effect of CaO and Fe t O in slags to form 3CaO·P2O5 and 4CaO·P2O5 until the carbon content is less than 0.036 pct during a top–bottom combined blown steelmaking process.

Some Investigations into the Dynamic Mass Transfer at the Slag–Metal Interface Using Sulfur: Concept of Interfacial Velocity

In the current work, dynamic studies of mass transfer of sulfur from the gas phase to the metal phase of pure iron through CaO-SiO2-Al2O3-FeO quaternary slag were carried out. X-ray videos were taken that were later processed to identify the oscillation of the metal drop occurring during the mass transfer. It was observed that the metal drop had hybrid oscillations. Each of these oscillations could be identified as composed of a symmetric and an asymmetric element, which was attributed to the changes in the shape of the droplet. The latter (asymmetric part) could be identified by the deviation of the left and right contact angles from the stable configuration. The symmetric oscillations were traced to the surface movement of sulfur at the interface, which created an instantaneous area change at the slag–metal interface. This area change was due to the combined effect of Marangoni flow and interface dilatation. The velocity of sulfur at the interface was calculated from the area change and had a maximum order of magnitude as 10−4 m/s. It was also observed that the interfacial velocity increased with increase in temperature.

Interfacial Phenomena in Metal–Slag–Gas System during AOD Process

Significance of interfacial phenomena and properties such as surface tension are essential in iron and steelmaking processes due to chemical reactions occurring on the interfaces including elements transfer through the phase boundaries. In this study, the influences of surface tensions of slag and metal and interfacial tension between slag and metal on the behavior of metal–slag–gas system were analysed based on the energy bound to system surfaces. Effects of reactions between slag and steel on the behavior of metal–slag–gas system during AOD process were evaluated by two cases: evaluation of top slag–steel melt system and single bubble rising in the metal bath.Simulations for metal–top slag system show that there are no possibilities to form metal film around the gas bubbles when they penetrate through metal–slag interface. Behavior of system is also independent of intensity of reactions between slag and steel. According to the calculations during intensive metal–slag reactions metal droplets are disintegrated more easily into top slag layer. If there are no metal–slag reactions metal droplets are attached into the gas bubbles.Calculations prove that, when reactive oxygen gas bubble forming oxides is injected into steel bath, slag film can be formed around the gas bubble if the intensity of reactions between the slag and the metal is high. During effective oxidation reactions at the vicinity of nozzles formed micro slag is attached with the rising gas bubble.

Optimisation of Steel Desulphurisation by Lime Powder Injection by Numerical Simulations

This paper focuses on the simulation of steel desulphurisation by lime powder injection. Thereby, the particle laden plume as well as additional gas stirring plumes are modelled by an multifluid Eulerian method. In addition, a transitional heterogeneous reaction is assumed to happen between the rising lime particles and the dissolved sulphur. Furthermore, a permanent reaction mechanism is defined at the metal-slag interface. With help of these macroscopic simulations the desulphurisation performance of a given ladle-lance-stirrer configuration can be estimated. Once the simulations are calibrated by steel plant experiments, these simulations should be able to hint to possible geometrical or operational improvements. Nevertheless, since a sound validation of the macroscopic simulation tool is not feasible many modelling uncertainties remain. Therefore, in a second part this paper focuses on the detailed modelling of the initial momentum of the injected powder which is critical for the powder penetration depth. In this context dedicated experiments are performed in order to substantiate the boundary conditions of the macroscopic simulations.

Fluid Flow and Interfacial Phenomenon of Slag and Metal in Continuous Casting Tundish With Argon Blowing

The fluid flow and the interfacial phenomenon of slag and metal in tundish with gas blowing were studied with mathematical and physical modeling, and the effects of gas flowrate, the placement of porous beam for the generation of bubbles, and the combination of flow control devices on the flow and slag-metal interface were investigated. The results show that the position of gas bubbling has a significant effect on the flow in tundish, and the placement of porous beam and gas flowrate are the two main factors affecting the entrapment of slag in tundish. The closer the porous beam to the weir, the more reasonable is the flow, which is in favor of the control of slag entrapment in tundish.

In situ studies of the agglomeration phenomena for calcium–alumina inclusions at liquid steel–liquid slag interface and in the slag

Studies of inclusion behavior at the metal–slag interface are of great importance for the steel industry in order to obtain better control of the size and of inclusions as well as improving the steel quality and casting process. In this work the agglomeration of liquid Al 2O 3–CaO particles at the liquid steel–liquid slag interfaces are studied with a confocal scanning laser microscope. In addition, the agglomeration of liquid Al 2O 3–CaO inclusions already transferred to the slag is investigated. It is found that agglomeration of the liquid inclusions at the steel–slag interface could only take place when the inclusions were forced towards each other, while the agglomeration of liquid particles was seen to be noticeably enhanced when the particles were already in the slag.