Steel Bath Research Articles

Application of New Generation Electromagnetic Stirring in Electric Arc Furnace

Today's electric arc furnace (EAF) normally operates with high power input and short tap-to-tap time and has high demands on the bath mixing capacity to improve the heat and mass transfer. A new generation of electromagnetic stirrer (ArcSave) for EAF operation has been developed by ABB Metallurgy and applied in the industrial furnaces. The stirrer installed underneath the furnace bottom creates a whole bath mixing effect thus accelerates the homogenization of the temperature and chemical composition of the steel. Two ArcSave systems have been installed in 2014. One has been installed on a 90 ton Eccentric Bottom Tapping (EBT) furnace for carbon steel production in the United States and the other installed on a 90 ton spout tapping furnace for stainless steel production in Sweden. The effect of ArcSave on the EAF process has been studied during the hot test period and the resulting performance has been compared based on 6-month-data without stirring and 6-month-data with ArcSave. This paper will present the detailed information of the investigation results obtained from these two installations. ArcSave speeds up the scrap and FeCr melt-down, reduces the scrap cave-ins, homogenizes the temperature and chemical composition of the steel bath, forces the metal/slag reactions closer to equilibrium state, increases the decarburization rate. ArcSave reduces the consumption of electric energy and increase the scrap yield which makes the electric arc furnace more cost effectiveness. ArcSave is a potential and reliable solution to improve the operation safety, increase the productivity, and reduce the cost.

Researches Regarding the Influence of Technological Parameters on the Alloying Efficiency in Powder Injection Process

The injection of the powdered materials into molten melts is a common practice in the metallurgical technology of steel refining and alloying. During process development, within the metal bath is formed a mixed three-phase with different structures depending on the parameters of the hydrodynamic injection. The “plume zone” represents a domain inside of the molten metal in which takes place the forming, coalescence and disintegration of the gas bubbles, that penetrate into the molten metal together with the powdered material. The “plume zone” is the primary contact zone between the powdered particles and the molten metal. Inside of contact zone is take place the chemical reactions between the reactive material and the metal bath components. The “plume zone” size, shape and structure are functions of the hydrodynamic parameters of the injection process, the most important being the injection speed. The size of this parameter leads at the appearance of a multitude of possible structures types of the metal bath. These structures dictate the metallurgical process efficiency in defining the steelmaking process and refining of metal bath. In the present paper are investigated and discussed the “plume zone” structures formed during injection with graphite particle of a molten steel bath and the metallurgical results obtained experimentally under the influence of the injection velocity.

Modelling Coalescence of a Particle Laden Bubble with a Bare Bubble in Steel Bath

The phenomenon of bubble coalescence is encountered along with the interaction of hydrophobic particles in metallurgical industries and flotation processes. In the context of steel making industries where inert gas bubbles are used to remove inclusions from steel, coalescence of bubbles was expected to show an effect on the stability of the particles or agglomerates at the bubble interface. This was verified by carrying out experiments using a cold model with polymeric low density polyethylene particles which are hydrophobic in nature. The effect of particle size and particle loading on coalescence of two equal sized bubbles, one bare and the other coated with particles has been investigated. It has been found that individual particles remained stable to bubble surface oscillations, however, agglomerated particles were unstable and their detachment had a dependency in particle size and loading fraction on the bubble.

Modeling of flow behaviour in a LD vessel by an impinging gas jet

Present study is focused towards development of computational fluid dynamic model of oxygen impingement in the melt pool in case of LD (basic oxygen converter) steelmaking process. 1/30th scaled down model of the 100 ton LD converter has been developed and flow simulation has been performed based on volume of fluid technique, using Fluent as solver engine. Simulation of the steel bath and oxygen is carried out by using water and air, respectively. Effect of process variables on the LD steelmaking practice has been studied and the findings ascertain penetration depth of the oxygen jet into the liquid (metal) pool as a strong function of bath (lance) height, gas flow rate and nozzle exit diameter. Furthermore, an equation is developed by carrying out regression analysis using results obtained from numerical simulation. The study also provides insight into the surface deformation modes, their onsets and transition regimes, which originates due to the gas impingement into the melt pool. Finally, the computed results are compared with the experimental findings for selected cases and good agreement has been found.

Morphology and composition changes of spinel (MgAl2O4) inclusions in steel

In this study, spinel inclusions of close to stoichiometric MgO.Al2O3 composition and known size distribution were added to a liquid steel bath before assessing their reactivity. The inclusions were then tracked for changes in size, morphology and composition with time in an aluminium killed steel at 1600°C, by sampling of the melt followed by automatic SEM based inclusion analysis techniques. The majority of the inclusions in the melt were alumina and complex sulphide inclusions, with the added spinel inclusions being a small proportion of the total inclusions. The proportion of alumina inclusions increased with time. The spinel inclusions were found to be evenly distributed through the melt and there was little change in their average size during the reaction. However, the composition of the inclusions did change, with the Mg/Al mass-% ratio changing from ∼0·5 to 0·08.

Synthesis of Highly Dispersed and Conductive Graphene Sheets by Exfoliation of Preheated Graphite in a Sealed Bath and its Applications to Polyimide Nanocomposites

E-mail: cnt@kist.re.kr Received January 28, 2014, Accepted March 17, 2014A simple method for exfoliating pristine graphite to yield mono-, bi-, and multi-layers of graphene sheets as ahighly concentrated (5.25 mg/mL) and yielded solution in an organic solvent was developed. Pre-thermaltreatment of pristine graphite at 900 °C in a sealed stainless steel bath under high pressures, followed bysonication in 1-methyl-2-pyrrolidinone solvent at elevated temperatures, produced a homogeneous, well-dispersed, and non-oxidized graphene solution with a low defect density. The electrical conductivities of thegraphene sheets were very high, up to 848 S/cm. These graphene sheets were used to fabricate graphene-polyimide nanocomposites, which displayed a higher electrical conductivity (1.37 S/m) with an improvedtensile strength (95 MPa). The synthesized graphene sheets and nanocomposites were characterized bytransmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray photo-electron spectroscopy, and Raman spectroscopy. Key Words : Graphene sheets, Thermal exfoliation, Polyimide nanocomposites, Electrical conductivity, Ten-sile strengthIntroductionGraphene is formed by a single atomic layer of sp

TiO<sub>2 </sub>Nanoparticle Addition into Molten Steel: From Lab Scale to Industrial Scale

In this work, the design of a new technology for nanoparticle addition into molten steel that improves the mechanical properties of the material, as well as the upscale of the process, was pursued. The process was scaled from laboratory to industrial level starting from first experiments carried out in pure iron bath, in order to analyze the behavior of nanoparticles in molten metal environment, and finishing with the addition of nanoparticles into microalloyed steel bath as industrial trials. The first steps of the research were performed in the levitation furnace at Tecnalia R&I installations that can cast samples up to 1 kg, continuing with a high vacuum furnace with a capacity up to 35 Kg. By the end of the investigation, the process was scaled up to industrial level at Gerdau facilities.

High yield and high concentration few-layer graphene sheets using solvent exfoliation of graphite with pre-thermal treatment in a sealed bath

We developed an efficient method for exfoliating pristine graphite in an organic solvent to produce a high yield (14%) and high concentration (5.25mg/mL) of well-dispersed mono-, bi-, and multi-layered graphene sheets. Pre-thermal activation of pristine graphite at 900°C in a sealed stainless steel bath under high pressure, followed by sonication in a solvent of 1-methyl-2-pyrrolidinone at elevated temperatures produced a solution of homogeneous, well-dispersed, defect-free, and non-oxidized graphene. The resulting electrical conductivities of the graphene sheets were high, up to 849S/cm.

Efficiency of Inclusion Absorption by Slags during Secondary Refining of Steel

One of the functions of secondary refining in steelmaking is to remove non-metallic inclusions produced through deoxidation of the steel bath during the process. Removal of these inclusions occurs in three fundamental stages: flotation, separation and dissolution of the inclusions in supernatant slag. Given that dissolution is subject to the action of slag, this study aims to clarify the inclusion absorption capacity of industrial slags and factors that influence slag properties in absorbing inclusions, as well as the impact of each factor on the cleanliness of the steels analyzed. To that end, the results of industrial steel and slag samples collected during the different stages of secondary refining were analyzed. The amount and chemical composition of the inclusions was determined by SEM/EDS (scanning electron microscopy coupled with energy-dispersive spectroscopy). The chemical composition of slag samples was measured by XRF (X-ray fluorescence) and subsequently submitted to thermodynamic simulations using FactSage 6.4 software. Calculations were made with the SlagViscosityPredictor, which uses FactSage 6.2 software. This made it possible to establish the chemical composition and proportion of the solid phase in the slags and inclusions, as well as the effective viscosity of the slags. The efficiency of absorption inclusion by the industrial slags was found to be greater in the presence of high thermodynamic driving force between slags and inclusions, low slag effective viscosity and when inclusions were not liquid.

Numerical Modeling of Inclusion Behavior in Liquid Metal Processing

Thermomechanical performance of metallic alloys is directly related to the metal cleanliness that has always been a challenge for metallurgists. During liquid metal processing, particles can grow or decrease in size either by mass transfer with the liquid phase or by agglomeration/fragmentation mechanisms. As a function of numerical density of inclusions and of the hydrodynamics of the reactor, different numerical modeling approaches are proposed; in the case of an isolated particle, the Lagrangian technique coupled with a dissolution model is applied, whereas in the opposite case of large inclusion phase concentration, the population balance equation must be solved. Three examples of numerical modeling studies achieved at Institut Jean Lamour are discussed. They illustrate the application of the Lagrangian technique (for isolated exogenous inclusion in titanium bath) and the Eulerian technique without or with the aggregation process: for precipitation and growing of inclusions at the solidification front of a Maraging steel, and for endogenous inclusions in the molten steel bath of a gas-stirred ladle, respectively.

Retainment, Recovery and Recycling: A Swedish Success Story of ECO-Steelmaking

With a view to optimize the environmental aspects of steelmaking, the Swedish Steel Producers Association took the initiative to start a national project on ECO-steelmaking with financial support from Swedish Foundation for Strategic Environmental Research. The Division of Materials Process Science at the Royal Institute of Technology has an important part of the project, viz. “Retention, Recovery and Recycling”, with emphasis on the retention of metal values in the steel bath without loss to the slag or gas phases, to recover the metal values that are lost to the slag phase by the development of new or optimized process concepts and aim at a total recycling of the metal values as well as the slag components within or outside the steel sector. The present paper describes the optimization of existing process concepts as well as evolving newer concepts to meet the above project goals. The use of CO2–O2–Ar gas mixtures for the decarburization of high-alloyed steels, development of a low cost precursor for the addition of molybdenum to steel in EAF, direct alloying in EAF are some of the concepts initiated in the present work. Successful recovery of iron and manganese values by oxidation of the slag and separation of the magnetite or manganese ferrate by electromagnetic separation formed part of the recovery part. As part of the project, a salt extraction process was developed by which the metal values in slags could be extracted into a chloride phase followed by electrolysis in fused chloride medium. This method was found to be successful in the recovery of metal values from slags. This process could be extended to the recovery of a variety of metal values from a variety of secondary sources. The salient features of the process designs and the results are presented in this paper.

Toward a Full Simulation of the Basic Oxygen Furnace: Deformation of the Bath Free Surface and Coupled Transfer Processes Associated with the Post-Combustion in the Gas Region

The present article treats different phenomena taking place in a steelmaking converter through the development of two separate models. The first model describes the cavity produced at the free surface of the metal bath by the high-speed impinging oxygen jet. The model is based on a zonal approach, where gas compressibility effects are taken into account only in the high velocity jet region, while elsewhere the gas is treated as incompressible. The volume of fluid (VOF) method is employed to follow the deformation of the bath free surface. Calculations are presented for two- and three-phase systems and compared against experimental data obtained in a cold model experiment presented in the literature. The influence on the size and shape of the cavity of various parameters and models (including the jet inlet boundary conditions, the VOF advection scheme, and the turbulence model) is studied. Next, the model is used to simulate the interaction of a supersonic oxygen jet with the surface of a liquid steel bath in a pilot-scale converter. The second model concentrates on fluid flow, heat transfer, and the post-combustion reaction in the gas phase above the metal bath. The model uses the simple chemical reaction scheme approach to describe the transport of the chemical species and takes into account the consumption of oxygen by the bath and thermal radiative transfer. The model predictions are in reasonable agreement with measurements collected in a laboratory experiment and in a pilot-scale furnace.

Foaming in Electric Arc Furnace—Part II: Foaming Visualization and Comparison with Plant Trials

The kinetics of slag foaming by limestone particles was studied at 1773 K (1500 °C) with the aid of an X-ray imaging system. Two models were implemented to describe the decrease in foam height with the time on the basis of the lowering of the average temperature and CaO shell formation during decomposition reaction. The energy impact of carbonate additions was studied on an industrial scale in a 100-ton electric arc furnace (EAF). It was found that, in the case of the addition of carbonates after the scrap is completely molten, the heat effects for limestone and dolomite (2255 and 2264 kJ/kg, respectively) were only 70 pct from theoretical values. Comparing these values with similar additions during the scrap melting stage shows that the energy requirements in the case of carbonate additions to steel bath are much smaller. It was found from the trial heats with dolomite addition to the steel bath that the partial substitution of lime by raw dolomite can be made without an increase in energy consumption.

Understanding stainless steelmaking through computational thermodynamics: Part 3 – AOD converting

The major issue in stainless steelmaking is the difficulty of oxidising carbon from molten steel without also oxidising large proportions of expensive chromium. This can, however, be achieved by reducing the partial pressure of the gaseous product of carbon oxidation, carbon monoxide, by dilution with argon. Modern stainless steelmaking is dominated by duplex processes which prepare a high carbon melt in an electric arc furnace, and then decarburise it in an argon–oxygen decarburisation (AOD) converter. In this work, the thermodynamic basis of preferential carbon oxidation by dilution of oxygen with argon is discussed, together with a review of AOD practice. The AOD process was simulated using computational thermodynamics software to illustrate the way in which it can achieve very low carbon levels in the molten steel bath without excessive co-oxidation of chromium. The slag reduction stage using ferrosilicon additions was also modelled and shown to be able to recover almost all oxidised chromium from the slag, limited only by the accompanying increase in the silicon content of the steel. The models, although simple and easy to develop, correctly predicted all trends in output variables as input parameters were changed and often matched plant data very well. The models provide a valuable learning tool for those interested in pyrometallurgical processing in general, and stainless steelmaking in particular.

Inclusion Removal at the Free Surface of Steel Bath by Bubble Flotation

In the present work, physical model experiments were carried out to clarify the inclusion removal at the free surface of steel bath. Polyethylene particles were used to simulate the non-wetting inclusions like alumina and silica. The influence of gas flow rate and bubble size on the inclusion removal at the free surface was evaluated. It is demonstrated that not all particles are removed when they arrive at the free surface of liquid bath, and those which are not removed will get back to the bath. It is found an annular particle layer is formed by the removed particles at free surface, which can capture other particles arriving at the free surface. However, the attachment of particles to the annular particle layer is not stable, and re-entrainment of particles occurs at high gas flow rate. It is shown the overall particle removal is determined by a balance of removal and re-entrainment. The particle removal constant increases with the increase in the gas flow rate, but decreases with the increase in bubble size. The equilibrium concentration of particles increases with the increase in gas flow rate and bubble size.

Bottom-Blown Stirring Technology Application in Consteel EAF

Bottom blown stirring technology application in EAF was studied in this paper. The basic principle of bottom blowing process was researched, the bottom blown stirring can give strong stirring effect on the molten steel bath, thus bath mixing time was shortened, decarburization and dephosphorization were improved, however over stirring would lead to liquid steel incontact with atmosphere air. Reasonable process was considered on Consteel EAF. results show that: with bottom-blown stirring technology, decarburization and dephosphorization increase significantly; oxygen and lime consumption decrease; content of FeO in final slag reduces; and heat time becomes short.

The influence of chromate quenching and chloride contamination level on the performance of the painted hot-dipped galvanized steel (duplex system)

The influences of the chromate quenching step and the surface chloride contamination levels of galvanized steel on the performance of duplex systems were studied. Steel panels were galvanized in a commercial steel bath adopting three different postdipping procedures. A comparative study of the galvanized steel, both painted and nonpainted, was performed by electrochemical techniques. It was verified that the chloride contamination level of the galvanized steel surfaces is the main cause of duplex system failures. An explanation for the influence of the chromate quenching on the performance of duplex systems was presented.

Mathematical and physical simulation of the interaction between a gas jet and a liquid free surface

In this work a two phase 3D mathematical model was developed using the volume of fluid (VOF) algorithm, which is able to accurately describe the cavity geometry and size as well as the liquid flow patterns created when a gas jet that impinges on a liquid free surface. These phenomena are commonly found in steelmaking operations such as in the Electric Arc Furnace (EAF) and the Basic Oxygen Furnace (BOF) where oxygen jets impinge on a steel bath and they control heat, momentum and mass transfer. The model was successfully validated with measurements made on a physical model through velocity fields obtained by Particle Image Velocimetry (PIV) and high speed camera images of the cavity. Agreement between model predictions and experimental measurements is excellent in both x-velocity component of the liquid and cavity sizes. The cavity formed in the liquid by the impinging jet depends on a force balance at the free surface where the inertial force of the jet governs this phenomena, while the liquid circulation depends on also the jet inertial force of the jet, but its angle plays an important role, being the lowest angle the best choice to shear the bath and promote stronger circulation and better mixing in the liquid.

Microstructural evolution of intermetallic layer in hot-dipped aluminide mild steel with silicon addition

Mild steel was coated by hot-dipping into molten pure aluminum, Al–0.5 Si, Al–2.5 Si, Al–5 Si and Al–10 Si (wt.%) baths at 700°C for 180seconds. The microstructure and phase constitution of the aluminide layers were characterized by means of optical microscope, scanning electron microscope with energy dispersive X-ray spectroscopy, X-ray diffraction and electron backscatter diffraction. Also, the thicknesses of the intermetallic layers and the metal losses of the steel substrate were measured to investigate the interaction between mild steel and aluminum baths. The results revealed that the additions of silicon to the aluminum baths caused Al7Fe2Si and Al2Fe3Si3 phases to form above the FeAl3 layer and in the Fe2Al5 layer, respectively. As the silicon content in the aluminum bath increased, the thickness of the intermetallic layer decreased, and the intermetallic layer/steel substrate interface transformed from an irregular morphology into a flat morphology. The decrease of the thickness of the intermetallic layer was principally attributed to the detachment of the Al7Fe2Si layer from the intermetallic layer into the aluminum bath. The flattened intermetallic layer/mild steel substrate interface was due to the formation of Al2Fe3Si3 precipitates in the Fe2Al5 layer by the serration-like steel substrate reacting with the Fe2Al5 layer containing solid-solute silicon.

UsING of CALCIUM MAGNESIUM ALUMINATE FLUX WITH HIGH MGO CONTENT TO IMPROVE secondary STEEL LADLE LIFE TIME

One of the most corroded zones in the secondary steel ladle is the contact area between the metallurgical slag and the refractory lining. The slag zone, even with specially designed Magnesia-Carbon and Doloma-Carbon bricks, is in many cases the life time limiting factor for the whole steel ladle. This makes repairs by gunning or intermediate slag zone replacements necessary. During the slag zone replacement the ladle has to be cooled down with further negative effect on the other parts of the ladle due to thermally induced stresses and consequently crack formation. In order to improve the life time of the slag zone, the impact of OPTIMET TM RG (FLUX B) and OPTIMET TM HM (FLUX C), novel synthetic Calcium Magnesium Aluminate Fluxes (CMA) with high MgO-content, has been studied. Thermodynamic simulations with the FactSage © software and laboratory experiments have been conducted. A traditional slag fluxing practice with fluorspar (CaF 2 ) has been compared with Calcium Aluminate (CA), LDSF ® RG (FLUX A), and with these novel synthetic fluxes with different MgO-contents. Calcium Magnesium Aluminate Fluxes (CMA) allow a quick formation of a homogeneous and liquid slag with a high capacity to absorb sulphur and oxide inclusions from the steel bath, very similar to Calcium Aluminate (CA). Calcium Magnesium Aluminate Fluxes (CMA) bring the MgO-content in the slag, right after tapping, close to the saturation concentration and minimise the dissolution of Magnesia-Carbon or Doloma-Carbon bricks in the slag. Life time increase of the slag zone can be expected. Calcium Magnesium Aluminate Fluxes (CMA) help to reduce the specific ladle costs per tonne of steel. The efficiency of high quality steel production can be increased which supports the efforts to reduce the CO 2 -emissions per ton of produced steel.