Slag-metal Interface Research Articles

Study on Splashing Mechanism in Basic Oxygen Furnace Based on Slag Foaming Modeling

Inappropriate slag foaming is the main cause of splashing in basic oxygen furnace (BOF). Through the physical modeling, the effects of slag–metal reaction rate, viscosity of slag, slag–metal interface tension, and lance height on the slag foaming are investigated, and further analyzed the relation between the extent of BOF slag foaming and splashing. Consequently, two patterns of overflowing splashing and eruptive splashing and their critical conditions are summarized. The experimental results indicate that gas released by slag–metal reaction is primarily responsible for slag foaming in BOF, and the maximum height of foamed slag increases with increasing reaction rate of slag–metal. Moreover, an increase in dynamic viscosity of slag prevents the foam structure transforming from spherical foam to polyhedral foam, and thus improves the maximum foaming ability of slag and the stability of foam structure. With decreasing slag–metal interface tension, the slag–metal emulsification and the stability of foam structure are promoted. Finally, it is concluded that overflowing splashing occurs under the conditions of the higher dynamic viscosity of slag and the larger gas generation amount; whereas, eruptive splashing occurs under the conditions of the lower dynamic viscosity of slag and the higher gas generation rate.

Large Eddy Simulation of Multi-Phase Flow and Slag Entrapment in Molds with Different Widths

Slag entrapment is a critical problem that affects the quality of steel. In this work, a three-dimensional model is established to simulate the slag entrapment phenomenon, mainly focusing on the slag entrapment phenomenon at the interface between slag and steel in molds with different widths. The large eddy simulation (LES) model and discrete particle model (DPM) are used to simulate the movements of bubbles. The interactions between phases involve two-way coupling. The accuracy of our mathematical model is validated by comparing slag–metal interface fluctuations with practical measurements. The results reveal that the average interface velocity and transverse velocity decrease as the mold width increases, however, they cannot represent the severity of slag entrapment at the interface between slag and steel. Due to the influence of bubble motion behavior, the maximum interface velocity increases with mold width and causes slag entrapment readily, which can reflect the severity of slag entrapment. On this basis, by monitoring the change of impact depths in different molds, a new dimensionless number “C” is found to reveal the severity of slag entrapment at the interface between slag and steel. The results show that the criterion number C increases with mold width, which is consistent with the results of flaw detection. Therefore, criterion number C can be used to reflect the severity of slag entrapment in different molds.

Interface Behavior and Interaction Mechanism between Vanadium-Titanium Magnetite Carbon Composite Briquette and Sinter in Softening-Melting-Dripping Process

As an innovative and promising BF iron-bearing burden, the vanadium-titanium magnetite carbon composite briquette (VTM-CCB) charging significantly affects the softening-melting-dripping characteristics and cohesive zone of the mixed burden. In this study, the interface behaviors between VTM-CCB and sinter were investigated by conducting interrupted softening-melting experiments to elucidate intrinsic structure evolution and interaction mechanisms. During softening, when the FC/O ratio of VTM-CCB ranges from 0.8 to 1.0, the molten slag-metal coexisting structure formed at the interface, thereby promoting the shrinking and decreasing T4 and T40. However, with increasing FC/O ratio higher than 1.0, the interface slagging and bonding would be suppressed due to the unconsumed carbon particles. During melting, the increasing of FC/O ratio would lower the FeO content and decrease the molten slag, and the interface layer transformed from molten slag-iron coexisting structure to dense metallic iron shell, suppressing the collapse of molten mixtures and increasing Ts. In the dripping process, increasing the FC/O ratio appropriately could promote the interface iron carburization and the aggregation of molten iron, thereby decreasing TD and improving the dripping performance. Besides, the VTM-CCB, acting as skeleton in the molten mixtures, could provide more gas channels to improve the permeability of packed bed. However, as the FC/O ratio exceeds 1.2, the Ti(C,N) would precipitate at the slag-metal interface and deteriorate the fluidity of molten mixtures, thereby deteriorating the gas permeability and increasing TD notably. Fully considering the softening-melting-dripping characteristics and the gas permeability, the appropriate FC/O ratio of VTM-CCB should not be higher than 1.2.

Multistage desulfurization mechanism to reduce sulfur content of high ferrotitanium prepared using thermite method

High ferrotitanium is used as a deoxidizer and alloying agent in steelmaking processes and is mainly produced using high-cost remelting processes. The thermite method is a simple and low-cost method for preparing low ferrotitanium. However, the high levels of S, Al, and O residues in the product severely restrict its applicability in the low-cost preparation of good-quality high ferrotitanium. In this study, a novel multistage deep reduction method for preparing high-quality high ferrotitanium is proposed, and the multistage desulfurization mechanism is systematically investigated. The results indicate that multistage desulfurization is an effective method for reducing the S content of high ferrotitanium prepared via the thermite method. During the strong desulfurization stage, Ti2S reacts with CaO at the slag–metal interface and produces CaS. The S content decreases, while the O content increases, with the increase of CaO in the CaO–Al2O3-based slag. During the deep desulfurization, Ti2S is deeply reduced by the Ca and produces CaS, thus further reducing the S content. The S content decreases with the incremental addition of Ca and can be reduced to 0.035 wt% after multistage desulfurization.

Insight into droplet formation in electroslag remelting process by numerical simulation

In this paper, a transient three-dimensional (3D) model is proposed to study the formation of metal droplets during electroslag remelting (ESR) process. The solution of the mass, momentum and energy conservation equations are simultaneously implemented with fully coupling electromagnetic field based on the finite volume method. The volume of fluid (VOF) model is used to capture the interface between slag and metal implicitly. Furthermore, the adaptive mesh refinement is adopted to improve the computational accuracy and efficiency. The model is firstly validated and then applied to industrial scale ESR process. Moreover, the simulation results illustrate that a two-stage process of the droplet formation occurs during the ESR process: the primary droplet formation and the satellite droplet formation. The primary droplet is formed by the gravity stretch, the pinch-off effect of the Lorentz force and surface tension. The formation process of the satellite droplet can be divided into two types: the tip pinch-off of the ligament controlled by the surface tension and the bifurcation of the ligament controlled by the Lorentz force. In addition, the effect of the metal-slag interface tension on the droplet formation is analyzed. The development of the model supports further understanding of the metallurgical reaction and non-metallic inclusion movement during ESR process.

Elucidating the Roles of SiO2 and MnO upon Decarburization During Submerged Arc Welding: A Thermodynamic Study into EH36 Shipbuilding Steel

By employing CaF2-SiO2 and CaF2-SiO2-MnO system fluxes, the roles of SiO2 and MnO in decarburization behaviors during submerged arc welding of EH36 shipbuilding steel have been quantified and evaluated. All possible reactions associated with C transfer and interfaces at which these reactions occur are systematically discussed. It is concluded that the addition of SiO2 and MnO exerts synergistic effects on the extent of decarburization due to increased partial pressures of O2 and SiO gases in the plasma, improved O level in the weld pool, and higher activities of the oxides, such as SiO2, MnO, and FeO, at the slag–metal interface. The investigation over the macrographic detached slag surfaces shows that the possibility of bubble nucleation is highly influenced by flux formula. The effect of heat input on decarburization is discussed, and the optimal flux compositions expected in the present study are analyzed.

A Numerical Investigation on the Electrochemical Behavior of CaO and Al2O3 in the ESR Slags

Field structures including electromagnetic, concentration of ions, and flow fields in an ESR-like process composed of a graphite crucible containing a molten slag, air, and an iron electrode are computed. Both CaF2—(mass pct 2) CaO and CaF2—(mass pct 2) Al2O3 slags are examined. Tertiary current distribution is calculated. Therefore, polarization overpotential and Faradic reactions at metal–slag interface are considered using Tafel law, whereas transport of ions in the bulk of slag is determined through Nernst–Planck equations. The main goal is to shed light on the invisible phenomena such as magnetohydrodynamics caused by transport of ions, electrical conductivity of CaF2-based slag using additives (e.g., CaO or Al2O3), and the role of complexation of ions (e.g., {text{AlO}}_{3}^{3 - } ) in the molten slag applied to the ESR. An explanation is given for the observation of higher oxygen content in the metal using Al2O3 than that using equivalent amount of CaO in the CaF2-based slag of a DC-operated ESR.

Physical and chemical bases of decarburization of high-carbon ferromanganese melt

The aim of the work is to establish physicochemical patterns of behavior of carbon, silicon, manganese when using the method of oxygen purge of high-carbon ferromanganese. Method. The process of blowing red metal to sour is neglected. With the fusion of fused acid, it is more important to oxidize silicon. Its presence in metal is practical in the block of oxidized manganese. Because oxygen is an assimilation gas, the mixing processes of the converter bath components and the reduction of manganese oxides at the metal-slag interface do not develop properly during purging. The smelters of the medium-carbonaceous ferromanganese in the converter are characterized by a stable chemical warehouse and even a higher number of vimogs for this type of alloy. The low concentration of silicon in metal over a number of swimming trunks can be easily shoved with a hat of pre-purge bathtub with sour at the final stage of refining. The behavior of phosphorus in these smelts is not controlled. The content of P2O5 in the final slag is 0.1%. To achieve acceptable concentrations of phosphorus in the metal, it is necessary to use starting materials with a low phosphorus content. Scientific novelty.Taking into consideration the high affinity of silicon for oxygen, the physical and chemical basis for the production of medium-carbon ferromanganese, as well as metallic manganese and low-carbon ferromanganese, is the process of the interaction of manganese oxides of a certain basicity slag melt with silicon dissolved in ferromanganese (manganese), that is, as combined reduction -refining process to produce manganese ferroalloys with a given silicon content standard

Physical and Mathematical Modeling of Flow Structures of Liquid Steel in Ladle Stirring Operations

Flow structures of liquid steel during stirring operations with argon injection in a ladle are studied using physical and mathematical models. Emphasis is made on the turbulent conditions near the metal-slag interface since this region is important for mass transfer and capture of inclusions by the slag phase. Experiments in a water model are analyzed through two multiphase models; the volume of fluid (VOF), and the Population Balance Model (PBM), which uses the input as the results provided by a Euler-Euler model. It is shown that the VOF model is accurately decomposed into the velocity fields of liquid and gas phases along the plume axis by the PBM model. Turbulent flow near the metal-slag interface is characterized by one and two-point correlations. Statistical correlations decrease under the presence of a top layer (slag). Fields of liquid velocities are well predicted by the VOF, and PBM models. Dimensionless velocity fields of the liquid lower phase, along the dimensionless plume height, can be correlated for a group of experiments or simulations but this procedure cannot be generalized. Increasing the thickness of the top layer breaks down all statistical correlations in the region near the interface. The VOF and PBM models are complementary and became the most suitable tools for ladle metallurgy furnace process-design and analysis.

CFD and Experimental Investigation of Desulfurization of Rejected Electrolytic Manganese Metal in Electroslag Remelting Process

An innovative electroslag remelting furnace with a water-cooled electrode was introduced to recycle the rejected electrolytic manganese metal (EMM) scrap. To clarify the desulfurization process in the rejected EMM scrap, a transient three-dimensional comprehensive numerical model was elaborated. Using the magnetic potential vector approach, the respective electromagnetic fields were calculated via the Maxwell equations. The Lorentz force and the Joule heating fields were derived as phase distribution functions and interrelated via the momentum and energy conservation equations as source terms, respectively. The molten manganese metal droplet motion, as well as the fluctuation of the slag–metal interface, was described by the volume-of-fluid (VOF) approach. Besides, the solidification was modeled via the enthalpy-based technique. A thermodynamic module was established to estimate the sulfur mass transfer rate between the molten manganese metal and the molten slag. Furthermore, a factor related to the magnitude and frequency of the alternating current and the physical properties of the melt was introduced to include the electro-emulsification phenomenon. An experiment has been carried out with a commercial-scale ESR device. The predicted values of the slag temperature and sulfur content in the final manganese ingot were found to agree reasonably with the corresponding measured data. Under continuous melting of the rejected EMM scrap, molten manganese metal droplets are formed at the domain inlet, grow, and fall down. Highly conductive molten manganese metal droplets significantly change distributions of the current streamline, the Joule heating, and the Lorentz force around and within it. Moreover, droplets are inclined to rotate and move inside the mold. With the renewal of the slag–manganese interface, sulfur in the molten manganese metal is constantly transferred to the molten slag. With the applied current ranging from 3000 to 4000 A, the average sulfur content of the manganese ingot dropped from 0.0447 to 0.0291 pct, and thus, the desulfurization rate rose from 55.3 to 70.9 pct.

Up-pulling force analysis for ESC hollow cylindrical casting

Electroslag casting (ESC) is an important method to produce high quality castings. In this study, the ESC up-pulling inner mold method (EUPIM) was used to produce hollow cylindrical castings with the multiple consumable electrodes. The radial deformation, the axial and radial internal stress of the inner mold, and the axial internal stress of the slag shell were analyzed using the finite element method (FEM) with the aid of ANSYS software. The ProCAST software was used to calculate the specific heat, heat conductivity and density curve of Cu. Simulation results show that the radial deformation, the axial and radial internal stress of the inner mold, and the axial internal stress of the slag shell near the slag-metal interface of hollow cylndrical casting gradually increase from 0 s to 360 s after the ESC starting (slagging) process but before applying the up-pulling force. The suitable initial up-pulling moment of the inner mold is at around 180–198 s after the starting process.

An Improved Dynamic Model of the Vanadium Extraction Process in Steelmaking Converters

The production process from iron ore to steel can be divided into several stages, among which the processes of vanadium extraction and steelmaking are two key technological sections. The products of vanadium extraction are important strategic resources for modern industrial countries, and the remaining molten iron after vanadium extraction provides the material used in the subsequent steelmaking processes. In some mechanism models of vanadium extraction and the steelmaking process, the contact area of the reactions is considered to be constant in the empirical formula; furthermore, even the masses of the molten steel and slag are taken to be constants. This paper presents an important improvement to the existing models, in which the contact areas of the slag–metal interface and the emulsion system are considered to be non-constant. The improved model is simple and easy to analyze theoretically. Theoretical analysis of the model equations can be used to explain the competitive oxidation between each element, as well as the oxygen conservation of the system. The numerical simulations are consistent with existing production data, showing that the mass fraction of vanadium can be reduced to the specified threshold after about 3.5 min of blowing, which provides an important reference for production control. Furthermore, it is shown that the model captures the “trapezoid” structure of the decarburization rate. This paper also considers the relationship between FeO and O, the numerical simulation partly reflecting the dependence between the concentrations of FeO and O. The improved model can be used to describe and predict the change of the molten steel and slag composition in the process of vanadium extraction, which provides a mathematical foundation for the automatic control of the vanadium extraction process.

Recycling silicon from silicon cutting waste by Al–Si alloying

Abstract Large amounts of silicon cutting waste (SCW) will be generated as the photovoltaic (PV) industry grows, which not only wastes valuable resources, but also causes environmental issues if SCW is not addressed. In this study, a novel and effective method to recycle Si from SCW by Al–Si alloying with a cryolite additive is proposed. The influence of the smelting parameters including smelting temperature, holding time and cryolite/SCW ratio, on the Si content of alloys and the utilization ratio of SCW was investigated and optimized. The optimal conditions were a smelting temperature of 1150 °C, holding time of 30 min and cryolite/SCW ratio of 6.3. Under these optimized conditions, the Si content of alloys and the utilization ratio of SCW were 12.02 wt% and 64.25%, respectively. The characterization analysis results of the products showed that Al–Si alloys with a uniform distribution of Si were successfully prepared. Furthermore, the mechanism of the alloying process was studied. Cryolite additives can efficiently dissolve the SiO2 film on the surface of Si particles and hence contribute to the subsequent transfer of the exposed Si to molten Al. The study of the slag-metal interface demonstrates that Si is recycled with a highly efficiency from SCW. Despite the relatively large amount of cryolite, the generated slag can be recycled and used as an additive for the next batch of experiments. This method not only recycles silicon scrap for use as valuable raw materials, but also reduces the production cost of Al–Si alloys, and thus, this method is a feasible way to commercially recycle SCW in an economically and environmentally friendly manner.

Numerical study on the effect of vacuum on oxygen transfer in electroslag remelting process

With increasing demands for high quality and ultra-low oxygen grade steel, the electroslag remelting process carried out under vacuum has been developed. A transient model coupling the magnetohydrodynamic flow, heat transfer and species transport was proposed to study the effect of vacuum on oxygen transfer during the electroslag remelting process. A reaction kinetic model was established to predict the mass transfer rates caused by the interfacial reactions. The predicted result agrees well with the experimental data. The oxygen is produced at the slag-metal interface due to the decomposition of Al2O3. The oxygen transfer is primarily achieved at the electrode-slag interface (ESI) and droplet-slag interface (DSI). The carbon deoxidization, which mainly occurs at DSI weakens the oxygen transfer from slag to steel, and can be promoted by lower pressure. The oxygen contents remelted under 101.325 kPa, 10 kPa and 1 kPa are 19.2 ppm, 15.5 ppm and 13.1 ppm, respectively. A low vacuum degree (no less than 10 kPa) is recommended regarding the stability of molten slag. The oxygen content increases from 14.3 ppm to 19.2 ppm with the carbon content ranging from 0.6% to 0.15%. The carbon deoxidization cannot occur when the carbon content is less than 0.15%.

Evaluation of carbide capacity in CaO-based ternary systems at 1773k for refining process

Refining slags is widely used in the production of high-value-added alloys and special steels. The removal of impurities depends on the mass transfer between the slag-metal interface, and the carbide capacity of the refining slags is crucial to control the carbon content in the final products. A phenomenological model is introduced in this article for the calculation of carbide capacity of different CaO-based ternary refining slags. The contour lines of carbide capacity in CaO-Al2O3- CaF2, CaO-SiO2-CaF2 CaO-SiO2-MnO systems are calculated based on limited experimental data by the present model. The experimental data within the calculation boundary are compared with the predicted values and satisfactory agreements are observed with the mean deviation being 1.4%, 2.3%, and 1.6%, for these three systems respectively. The present model is powerful and flexible in the calculation of carbide capacity of CaO-based ternary refining slags and can be applied to other systems.

Migration behaviors and kinetics of phosphorus during coal-based reduction of high-phosphorus oolitic iron ore

To understand the migration mechanisms of phosphorus (P) during coal-based reduction, a high-phosphorus oolitic iron ore was reduced by coal under various experimental conditions. The migration characteristics and kinetics of P were investigated by a field-emission electron probe microanalyzer (FE-EPMA) and using the basic principle of solid phase mass transfer, respectively. Experimental results showed that the P transferred from the slag to the metallic phase during reduction, and the migration process could be divided into three stages: phosphorus diffusing from the slag to the metallic interface, the formation of Fe-P compounds at the slag-metal interface and P diffusing from the slag-metal interface to the metallic interior. The reduction time and temperature significantly influenced the phosphorus content of the metallic and slag phases. The P content of the metallic phase increased with increasing reduction time and temperature, while that of the slag phase gradually decreased. The P diffusion constant and activation energy were determined and a migration kinetics model of P in coal-based reduction was proposed. P diffusion in the metallic phase was the controlling step of the P migration.

Investigation of desulfurization of Inconel 718 superalloys by ESR type slags with different TiO2 content

In the present study, effect of CaF2–CaO–Al2O3–MgO–TiO2 slag with various TiO2 contents on the desulfurization of Inconel 718 alloy was investigated at 1773K to provide the fundamental information for the establishment of desulfurization procedure during electroslag remelting (ESR) process. The melt-quenching method did not accurately determine the change in content of sulfur and oxygen in the nickel-based alloy with time for the present study, which uses a novel experimental apparatus. The results indicated that the final sulfur content in the nickel-based alloy increased from 7 to 9ppm when the TiO2 content in slag of CaF2–CaO–Al2O3–MgO–TiO2 system increased from 2.17 to 10% without addition of deoxidizer. In order to further expound the desulfurization mechanism, meanwhile, the relationship between the oxygen activity at slag–metal interface and reaction time under conditions of various TiO2 in the slag was studied by coupling with the developed mass transfer model. The calculated oxygen content in bulk metal has a good corresponding relationship with the measured oxygen content in the nickel-based alloy. The oxygen activity at slag–metal interface increased up to 9.6ppm when TiO2 content was 10% in the slag, giving rise to the decrease in desulfurization ratio in high TiO2 content. The optimal condition for simultaneously ensuring low sulfur content and maintaining oxidative elements, such as Al and Ti, uniformly from bottom to top of the ESR ingot is also discussed.

Fluid Flow Turbulence in the Proximities of the Metal-Slag Interface in Ladle Stirring Operations

Three-phase interactions (metal-slag-argon) in ladle stirring operations have strong effects on the metal-slag mass transfer processes. Specifically, the thickness of the slag controls the fluid turbulence to an extent that once trespassing a critical thickness, increases of stirring strength no longer effect the flow. To analyze these conditions, a physical model considering the three phases was built to study liquid turbulence in the proximities of the metal-slag interface. A velocity probe placed close to the interface permitted the continuous monitoring and statistical analyses of any turbulence. The slag eye opening was found to be strongly dependent on the stirring conditions, and the mixing times decreased with thin slag thicknesses. Slag entrainment was enhanced with thick slag layers and high flow rates of the gas phase. A multiphase model was developed to simulate these results and was found to be a good agreement between experimental and numerical results.

Development of Speciality Grade Wire by Controlling the Inclusions in High-Carbon Steel Using Synthetic Slag Treatment

The high-carbon wire rods essentially permit controlled traces of the aluminium and calcium dissolved in the molten steel bath due to the generation of un-deformable complex oxide inclusions. These inclusions can be controlled by treating the liquid steel with suitable synthetic slag. In the present investigation, slag with suitable composition was synthetically prepared based on the thermodynamic study. After melting the plant wire rods, synthetic slag was added in the bath and slag–metal reactions were carried out at around 1600 °C for a pre-specified period. Experimental results showed significant improvement in inclusion rating of hot-rolled specimens prepared by induction melting for the residence time of about 30 min across the slag–metal reaction. It thus depicts that slag–metal reaction residence time of 15 min is rather less than the residence time of 30 min for any significant improvement in inclusion rating under identical reactions across the slag–metal interface.

Effect of Slag Layer on the Multiphase Interaction in a Converter

A supersonic oxygen jet impinging onto the slag–metal interface is studied using computational fluid dynamics modeling with the aim of obtaining a better understanding of the multiphase interaction behavior in a converter. The dynamic interaction behavior as well as the effects of the slag thickness, viscosity, and surface tension are studied numerically. The results show that the geometrical dimensions of the cavity generated by the multiphase interaction decrease with increasing slag thickness. The presence of the slag layer can restrain splashing and droplet generation in the converter. However, the slag viscosity and surface tension have little effect on the momentum of the multiphase interaction, especially in the area away from the interaction zone under the present simulation conditions. The splashing behavior is not sensitive to the slag properties. The droplet generation rate changes slightly with variation of the slag viscosity and surface tension.