Showing papers in "Isij International in 2014"

Phase-field Modeling and Simulations of Dendrite Growth

Abstract: The phase-field method has recently emerged as the most powerful computational tool for simulating complicated dendrite growth. However, these simulations are still limited to two-dimensional or small three-dimensional spaces; therefore, to realistic and practical dendritic structures, it is crucial to develop a large-scale phase-field simulation technique. This review discusses the phase-field modeling and simulations of dendrite growth from the fundamental model to cutting-edge very-large-scale simulations. First, phase-field models for the dendrite growth of pure materials and binary alloys and their histories are summarized. Then, models and studies of interface anisotropy, polycrystalline solidification, and solidification with convection, which are very important in dendritic solidification, are reviewed. Finally, by introducing very-large-scale phase-field simulations performed recently using a graphics processing unit supercomputer, the power, potential and importance of the very-large-scale phase-field simulation are emphasized.

Tensile Behavior of Ti,Mo-added Low Carbon Steels with Interphase Precipitation

Abstract: Tensile behavior and structure-property relationship of ferritic steels with nano-sized carbide dispersion were invesigated using Ti-added steel and Ti,Mo-added low carbon steels By austenitizing followed by isothermal heat treatment at 700°C, polygonal ferrites containing very fine carbides of TiC and (Ti,Mo)C were obtained in the Ti-added and the Ti,Mo-added steels, respectively The size of such carbides was finer in the Ti,Mo-added steel than in the Ti-added steel at the same isothermal holding The results of tensile tests for these samples showed that the strength is higher as the carbide size is smaller The structure-based strength calculation led to a good agreement with the experiments, when it was assumed that the Ashby-Orowan mechanism is dominant for precipitation strengthening of nano-sized alloy carbides It was also suggested that a relatively large tensile ductility is related to enhanced recovery during the tensile deformation, accompanied with promotion of secondary slips or cross slips in a finer scale due to the nano-sized particles

Structure-Viscosity Relationship of Low-silica Calcium Aluminosilicate Melts

Abstract: The structure-viscosity relationship of the low-silica (SiO2 ≤ 10 wt%) calcium aluminosilicate melts, which represent the secondary refining ladle slag systems, was investigated by employing the rotatingcylinder viscosity measurement in conjunction with the Raman spectroscopy measurement for linking the macroscopic thermophysical property and molecular (ionic) structural information. Furthermore, the influence of CaF2 on the structure-property relationship was explored. The viscosity of low-silica calcium aluminosilicate melts decreased with increasing both CaO/Al2O3 and CaO/SiO2 ratios. However, the effect of the former on the viscosity of low-silica calcium aluminosilicate melts was larger than that of the latter. By employing the Neuville’s structure model, in which the silicate structural units with various NBO, i.e. QSi are located at the boundary of the AlO4 aluminate, and the Raman scattering data of the glass samples, it was demonstrated that the aluminate and silicate units are more effectively modified by increasing the CaO/Al2O3 ratio at fixed silica content. The addition of small amounts of CaF2 (~5 wt%) to the low-silica calcium aluminosilicate melts decreased the viscosity of the melts. From the analysis of Raman scattering data, the liberation of SiO4 (QSi) units from the AlO4 aluminate structure by addition of CaF2 was understood. However, the effect of CaF2 addition on the viscosity became less discernible at higher CaF2 content (≥ 10 wt%) region, where the F ions simply substitute for the non-bridging oxygen ions in AlO4 tetrahedra.

Transient Evolution of Inclusions during Calcium Modification in Linepipe Steels

Abstract: The laboratory experiments of Al2O3 inclusions modified by calcium treatment in linepipe steels with the S content of 30 ppm and 310 ppm were performed at 1 873 K. Particularly, samples were taken before calcium treatment ( 1 minute before the calcium addition) and at various times (typically 1 minute, 10 minutes and 30 minutes) after calcium treatment to study the transient inclusions evolution during calcium modification. Traditional modification mechanism of Al2O3 inclusions is that Al2O3 inclusion is directly modified by dissolved calcium or indirectly modified via CaO formed from calcium and oxygen. In the current study, after Ca–Si alloy power addition, CaS outer layer were promptly formed on the angular Al2O3 inclusion. With the reaction of the CaS outer layer and the Al2O3 core or [O], the Al2O3 inclusion was modified to a spherical liquid calcium aluminate. Moreover, the equilibrium curve of Ca–O and Ca–S, the stability diagram of inclusions and equilibrium precipitation of inclusions during solidification in linepipe steels were calculated to study the formation of inclusions.

Dissolution Behavior of Mg from MgO into Molten Steel Deoxidized by Al

Abstract: 1) Graduate Student, Department of Metallurgy, Graduate School of Engineering, Tohoku University, 2-1-1 Katahira Aoba-ku, Sendai City, 980-8577 Japan. 2) Formerly Graduate Student, Department of Metallurgy, Graduate School of Engineering, Tohoku University. Now at Research & Development Division, UACJ Corporation, 1351 Uwanodai, Fukaya City, 366-8511 Japan. 3) Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira Aobaku, Sendai City, 980-8577 Japan.

Recent Progress on Advanced Blast Furnace Mathematical Models Based on Discrete Method

Abstract: From the backgrounds of the recent trends towards low reducing agent operation of large blast furnaces and application of diversified charging modes for various burdens, an advanced mathematical model of the blast furnace is required. Although conventional models based on the continuum model have been widely used, these models are not sufficient for the recent demands. Discrete models such as discrete element model (DEM) and particle method are expected to enable precisely simulation of the discontinuous and inhomogeneous phenomena in the recent operating conditions. With discrete models, microscopic information on each particle in the packed bed can be obtained in addition to the overall phenomena in the blast furnace. Visual information for understanding in-furnace phenomena can be also obtained with high spatial resolution. Liquid dripping and the movement of fines in the lower part of the blast furnace can be simulated with high accuracy by using DEM and particle methods such as the Moving Particle Semi-implicit Method (MPS). Moreover, the optimum bed structure for low reducing agent operation is being clarified by application of the Eulerian-Lagrangian method. This review summarizes recent progress on the mathematical models based on the discrete model.

Analysis and Application of Soft Reduction Amount for Bloom Continuous Casting Process

Abstract: Based on the principle of solidification shrinkage compensation, a soft reduction amount calculation method was derived for bloom continuous casting process, and the bearing steel GCr15 was chosen as specific research steel to describe calculation process in detail. A two-dimensional heat transfer model was built to predict the solidification process of bloom, and the material properties of GCr15 were derived by weighted averaging of the phase fractions. The predicted temperature and shell thickness were verified by a thermal infrared camera and nail shooting results, respectively. The soft reduction amount of typical high carbon alloy steel blooms were calculated and discussed. The plant results showed that after the application of soft reduction to the bloom, centerline segregation and “V” type segregation were improved significantly. The carbon and sulfur ratios of the bloom centerline were reduced from 1.39 to 1.09 and 2.14 to 1.29, respectively.

Effect of Mg and Ca Treatment on Behavior and Particle Size of Inclusions in Bearing Steels

Abstract: 1) State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Room 1012, Metallurgical Building of University of Science and Technology in Beijing, No. 30, Xueyuan Road, Haidian District, Beijing, 100083 China. 2) School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Room 1012, Metallurgical Building of University of Science and Technology in Beijing, No. 30, Xueyuan Road, Haidian District, Beijing, 100083 China.

Measurements of Molten Steel Surface Velocity and Effect of Stopper-rod Movement on Transient Multiphase Fluid Flow in Continuous Casting

Abstract: Surface velocity of the molten steel in the mold is critical to final product quality during continuous casting of steel, and is one of the few flow parameters that can be measured in the plant to validate fluid flow models. Surface velocity was measured using two different sensors: Sub-meniscus Velocity Control (SVC) devices and nail dipping, to evaluate their performance, and to quantify surface velocities in a commercial steel caster under different casting speeds, argon gas fractions, and mold widths. A correlation between the height difference of the solidified lump on the nail and surface velocity is confirmed and extended. Reasonable agreement between the two sensing methods was obtained, both in trends and magnitudes for both time-averaged velocity and transient flows. Transient CFD models are applied to simulate multiphase flow of steel and gas bubbles in the Submerged Entry Nozzle (SEN) and mold and are validated with nail dipping measurements. To obtain the transient inlet boundary conditions for the simulation, two semi-empirical models, a stopper-position-based model and a metal-level-based model, predict the liquid steel flow rate through the SEN based on recorded plant data. The model system was applied to study the effects of stopper rod movements on transient flow in the SEN and mold. Mold level fluctuations were calculated using a simple pressure method and compared with plant measurements. The results show that severe stopper rod movements cause significant disturbances of the meniscus level, which may cause slag entrapment, leading to sliver defects in the final product.

Effect of Slag Properties on Mixing Phenomena in Gas-stirred Ladles by Physical Modeling

Abstract: The effect of slag properties (thickness and viscosity), have been evaluated in terms of mixing time, exposed surface or ladle eye and energy dissipation. A nozzle configuration defined in terms of the number of nozzles, its radial position and gas flow rate has been employed to describe the influence of the top layer on mixing phenomena. It has been found a negative effect of both slag thickness and slag viscosity on mixing time, on the other hand, the same properties are useful to decrease the exposed surface or ladle eye. An empirical approach using water modeling is suggested to evaluate the average velocity of the bulk liquid. The method was used to define the fraction of stirring energy consumed by the top layer. The result is in agreement with a previous investigation.

Transient Fluid Flow during Steady Continuous Casting of Steel Slabs: Part I. Measurements and Modeling of Two-phase Flow

Abstract: (DPM) for argon gas injection. The surface level of the molten steel fluctuates due to sloshing and shows greater fluctuations near the nozzle. The slag level fluctuates with time according to the lifting force of the molten steel motion below. Surface flow shows a classic double roll pattern with transient cross-flow between the Inside Radius (IR) and the Outside Radius (OR), and varies with fluctuations up to ~50% of the average velocity magnitude. The LES results suggest that these transient phenomena at the surface are induced by up-and-down jet wobbling caused by transient swirl in the slide-gate nozzle. The jet wobbling influences transient argon gas distribution and the location of jet impingement on the Narrow Face (NF), resulting in variations of surface level and velocity. A power-spectrum analysis of the predicted jet velocity revealed strong peaks at several characteristic frequencies from 0.5–2 Hz (0.5–2 sec).

Modeling the Gas-solid Flow in the Reduction Shaft of COREX

Abstract: COREX is a promising alternative to blast furnace ironmaking. It includes two main reactors: a reduction shaft (RS) for the direct reduction of iron ore and a melter gasifier for the melting reduction of directly reduced iron. This work uses a two-dimensional slot model to investigate the gas-solid flow in the RS by a combined computational fluid dynamics and discrete element method approach. The three-dimensional flow of cohesive solids is then examined for three RS designs by the discrete element method. The effects of gas flow, the stickiness between particles, the rotational speed of screws, and different designs are depicted in terms of gas-solid flow pattern, overall bed pressure drop and solid flowrate. The results show that the effect of gas flow is insignificant on gas-solid flow pattern due to the small gas-solid interaction forces under the considered conditions. Solid flow varies in a complex manner with the rotational speed of screws and the sticking force, and a correlation is formulated for predicting the solid flowrate based on the simulated results. It is also shown that the effect of geometrical design on solid flow is complicated and significant. Caution should be taken for any changes in the design. The findings should be useful for the design, control and optimization of the RS operation.

3D Coupled Cellular Automaton (CA)–Finite Element (FE) Modeling for Solidification Grain Structures in Gas Tungsten Arc Welding (GTAW)

Abstract: A coupled Cellular Automaton (CA) – Finite Element (FE) model is proposed to predict the grain structure formation during Gas Tungsten Arc Welding (GTAW). The FE model solves the heat flow problem based on an adaptive meshing. This is done on a first FE mesh. The CA model simulates the development of the envelope of the grains in the liquid. For that purpose, a second FE mesh, referred to as CA mesh, is used. Fields can be interpolated between the adaptive FE mesh and the CA mesh. A CA grid made of a regular lattice of cubic cells is defined and superimposed onto the CA mesh. A new dynamic strategy for the allocation/ deallocation of the CA grid is proposed to reduce the computation and memory costs. This CAFE model is applied to partial melting of an initial grain structure and epitaxial growth in the undercooled zone of a liquid pool, thus simulating the formation of solidification structure during the GTAW process. Examples of single linear passes simulations for various processing conditions and a multiple pass simulation are presented.

Influencing Factors and Effects of Assimilation Characteristic of Iron Ores in Sintering Process

Abstract: Iron ore’s assimilation characteristic reflecting the beginning formation temperature of liquid phase in sintering process plays very important role on the fluidity of liquid phase and bonding strength of sinter body. Experimental study of assimilation characteristics of 12 kinds of iron ores were conducted using micro-sinter equipment, and pure reagent simulating tests of assimilation characteristic were also carried out for the purpose of achieving the influence of chemical composition on the assimilation characteristic. In addition, effects of assimilation characteristic of iron ore on the fluidity and bonding capacity of bonding phase were also researched. This study showed that SiO2 and LOI promoted the assimilation of iron ore, low Al2O3 (<1.5 mass%) was good to the assimilation, but high Al2O3 (≥1.5 mass%) was bad, MgO was adverse to assimilation of magnetite concentrate. In addition, lower assimilation temperature of iron ore led to higher superheat degree of liquid phase at a certain sintering temperature, then higher liquid fluidity and bonding strength.

Toughness and Microstructure of Coarse Grain Heat Affected Zone with High Heat Input Welding in Zr-bearing Low Carbon Steel

Abstract: The microstructure and toughness of simulated coarse grained heat affected zone (CGHAZ) in low carbon steel have been investigated in this study. In order to simulate microstructure evolution in CGHAZ, specimens were subject to weld thermal cycle with heat input of 100 kJ/cm, 400 kJ/cm and 800 kJ/cm at 1 400°C peak temperature using thermal simulator. As increase in heat input energy of weld thermal cycle, prior austenite grain size increases due to longer holding time at peak temperature. Excellent impact toughness of CGHAZ with heat input of 800 kJ/cm was obtained because of high volume fraction of fine acicular ferrite (AF) inside gain acting as an obstacle to cleavage propagation owe to its high angle grain boundary, forcing cleavage crack to change the route of propagation and effectively impedes the propagation of crack. The primary AF mainly originated from Zr-oxide particle with MnS and subsequently secondary AF nucleated sympathetically in form of side arms and grew from the primary AF in CGHAZ.

Effect of Micro-porosities on Fatigue Behavior in Aluminum Die Castings by 3D X-ray Tomography Inspection

Abstract: In this investigation, porosities in fatigue specimens obtained from practical ADC12 high pressure die castings were detected and reconstructed with high resolution X-ray computed tomography technology. Three dimensional (3D) characterizations of the porosities were analyzed. The high cycle fatigue tests were carried out at five stress amplitudes on seven groups of the specimens with different porosity contents. The Weibull analysis suggested less scatter of the fatigue life at larger stress condition. With the SEM observation on the fatigue fractured surfaces, the porosities initializing the fatigue cracks were identified. A pore-fatigue life prediction equation was deduced with the pore characteristics from the fracture surface and 3D X-ray tomography inspection. With 3D reconstruction of tomography data and FEA method, the simulation of the stress distribution around the actual 3D pores were carried out and analyzed further.

Thermal Decomposition Behaviour of Fine Iron Ore Particles

Abstract: In the smelting cyclone of HIsarna process, both thermal decomposition and gaseous reduction of iron ore contribute to the expected pre-reduction degree about 20%. However, the fine ore reduction and melting process in the smelting cyclone is extremely fast and it is very difficult to differentiate between the thermal decomposition and gaseous reduction. This study focused on the thermal decomposition mechanism of the fine iron ore under different conditions. Firstly, the theoretical evaluation has been conducted based on the thermodynamics, and then the laboratory investigation was conducted in three stages with three reactors: the TGA-DSC, the electrically heated horizontal tube furnace and the High-temperature Drop Tube Furnace (HDTF). According to the experimental results of the first two stages and the theoretical evaluation, it was found that the temperature of intensive thermal decomposition of Fe2O3 in the inert gas environment is in the range of 1 473–1 573 K, while the thermal decomposition of Fe3O4 could be sped up when the temperature is above 1 773 K in the inert gas. Temperature plays an important role in the thermal decomposition degree and reaction rate. Finally, it was found that the thermal decomposition of the individual iron ore particles took place very rapidly in the HDTF and no significant influence of the particle size and residence time (t ≤ 2 020 ms) on the equivalent reduction degree could be observed, when the particle diameter was smaller than 250 μm in the CO2 gas.

Fundamental Experiment to Extract Phosphorous Selectively from Steelmaking Slag by Leaching

Abstract: Steelmaking slag, including hot metal dephosphorization slag, is usually in the dicalcium silicate (C2S) saturated composition range. C2S is known to form a pseudo-binary solid solution with tricalcium phosphate (C3P) over a wide composition range, and most of the phosphorus in the slag forms a solid solution. The authors investigated the dissolution behavior of the solid solution and matrix phases in aqueous solutions, and the dissolution ratio of each element in matrix phase was much lower than that in the solid solution at every pH. To clarify the possibility of selective extraction of the solid solution from slag, leaching experiments were conducted on the steelmaking slag. The CaO–SiO2–Fe2O3 steelmaking slag system was made by a mixture of reagents and ground into particles smaller than 53 μm. After immersion, holes were observed on the surface of the slag particles. The area that selectively dissolved is considered as the solid solution phase prior to leaching. At pH 3, most of the Ca and Si in the solid solution dissolved after 120 min; however, the dissolution ratio of P was approximately 65% smaller than that of Ca. Compared to the matrix composition, the CaO/SiO2 ratio in the residue was close to the matrix and P2O5/Fe2O3 ratio was slightly larger than that of the matrix. XRD analysis revealed that the peak corresponding to the solid solution disappeared in the residue. The mass ratio of the residue to the dissolved slag was close to the ratio of the matrix to the solid solution before leaching.

Relationship between Molten Oxide Structure and Thermal Conductivity in the CaO–SiO2–B2O3 System

Abstract: Using a transient hot-wire method, the thermal conductivity of the CaO–SiO2–B2O3 mold flux system was measured. The effects of temperature, BO1.5 concentration and basicity on the thermal conductivity were considered, along with structural investigation by Raman spectroscopy. It was found that the addition of boron oxide caused both a decrement and increment of thermal conductivity, depending on the basicity. These conflicting effects on thermal conductivity were considered to be caused by the following two different behaviors in the oxide melts. Boron oxide is incorporated into silicate networks at a lower basicity, while it tends to form borate networks at higher CaO/SiO2 ratios. In the case of basicity dependency, thermal conductivity initially decreases or remains constant with increasing CaO/SiO2 ratio in regions of low basicity, but increases when the CaO/SiO2 ratio is higher than 1.15. Due to the incorporated state of boron oxide in silicate networks at low basicity, the thermal conductivity is likely to be predominantly affected by the silicate networks. However, at a relatively high CaO/SiO2 ratio, an increase in chain-type metaborate was observed through Raman spectroscopy; this structural change in borate being responsible for the increment in thermal conductivity with higher basicity. Finally, the apparent activation energy of thermal conductivity was calculated, and was found to be reduced by the addition of boron oxide.

Novel Process of Ferronickel Nugget Production from Nickel Laterite by Semi-molten State Reduction

Abstract: Rotary kiln-electric furnace (RKEF) process is the main technology to deal with nickel laterite for the ferronickel alloy production in the world. However, this process needs huge amount of electric power due to the large ratio of slag to metal. Therefore, a novel process was proposed to directly produce ferronickel alloy nugget at a related low temperature from nickel laterite by the semi-molten reduction in the reactor like the rotary hearth furnace (RHF). The effects of temperature and basicity of the slag on the separation between the slag and metal were investigated, the results revealed that it is reasonable to achieve the ferronickel alloy nugget directly at 1 400°C when the quaternary basicity ((mCaO+mMgO)/(mSiO2+mAl2O3)) was fixed at 0.60. Bad wettability of the refractory by the slag is good for the discharge of product from RHF and avoiding the corrosion of the slag. The high-temp wettability of refractory materials by the molten slag was also carried out with the sessile drop method, the results shows that the wettability order of the refractory by the slag from good to bad is Al2O3, MgO and graphite. It seems that the graphite is the suitable refractor material for bottom of RHF. However, the anti-oxidation of the graphite in the charging and discharging area is another potential problem which needs further study.

Effect of Al Content on the Characteristics of Inclusions in Al–Ti Complex Deoxidized Steel with Calcium Treatment

Abstract: To improve the effect of calcium treatment and the cleanliness of steel and to make use of fine TiOx to refine the microstructure of steel, the effect of aluminum content on inclusion characteristics of aluminum-titanium complex deoxidized and calcium treated steel is investigated based on the experiment with SEM/EDS, Image Pro-Plus 6.0 and FactSage 6.1 softwares and thermodynamic calculation in the present work. The results show that the inclusions in two steels with different aluminum content are obviously spherical composite inclusions with a two-layer complex structure, consisting of an Al2O3–CaO–TiOX core surrounded by MnS. In low aluminum steel, the oxide core of inclusions contains much TiOx and CaO, and their composite structure is mosaic compared with bundle in high aluminum steel, the number of inclusions is 2.5 times more than that in high aluminum steel, the thickness of MnS on oxides surface is also thinner. In addition, melting point of the inclusions in low aluminum steel is lower, the cleanliness of the steel is relatively improved because of the inclusions floating up, and the deformation aspect ratio of calcium aluminate inclusions with a certain amount of Ti2O3 is effectively improved, which is about 1–2 while the composition of oxide core is xAl2O3 = 35–55%, xTi2O3 = 15–35%, and xCaO = 10–25%. As a result, less calcium is needed to modify the alumina inclusions to liquid calcium aluminate in the case of lower aluminum deoxidized steel, thus the calcium treatment effect can be improved. The low aluminum in steel is more effective to control the inclusion characteristics to reduce the harm of MnS and to improve the cleanliness of steel.

Prediction of Bainite Start Temperature in Alloy Steels with Different Grain Sizes

Abstract: Bainite microstructure in alloy steels yields materials with an excellent combination of mechanical properties such as high strength and toughness, resistance to creep and fatigue, and hydrogen embrittlement.1,2) During cooling, bainite transformation is initiated at the bainite start (Bs) temperature, which is the highest isothermal temperature at which upper bainite is observed, and ceases when the temperature reaches the martensite start (Ms) temperature. Addition of alloying elements mostly lowers the Bs temperature. Especially, carbon and manganese known as strong austenite stabilizing elements effectively decrease the Bs temperature. Several quantitative investigations have been performed to determine the relationship between the addition of alloying elements and Bs temperature variations in alloy steels. Some empirical equations have been proposed to predict the effect of adding alloying elements to carbon and alloy steels on Bs temperature.3–12) Prior austenite grain size (PAGS) can also affect the Bs temperature. Lee et al.13) reported that Bs temperature decreased with decreasing PAGS. Bs temperature variations due to the decrease in PAGS simultaneously influenced bainite transformation kinetics.13–15) However, few researchers have attempted to develop the equations for Bs temperature by considering both chemical composition and PAGS effects. Therefore, in the present study, we developed a simple empirical equation for Bs temperature prediction that includes both the alloying element effect and the PAGS effect based on experimental data obtained from the literature. We compared the accuracy of our empirical equation with existing equations and verified the performance of our equation using experimental data. Experimental Bs temperature data for carbon and alloy steels were extracted from published time-temperaturetransformation (TTT) diagrams.16) Both chemical composition and PAGS were used to evaluate existing equations and to derive a new equation. We selected the following alloying elements in the present work: C, Mn, Si, Ni, Cr, and Mo. Data for other alloying elements were excluded. The chemical composition range of the selected steels was limited to that of low alloy steels, thus high alloyed steels such as a stainless steel was excluded. Ranges of chemical composition, PAGS, and Bs temperature used for equation derivation are summarized in Table 1. The total number of Bs data points used in the present work was 97. The effects of alloying elements on Bs temperature prediction are generally expressed by a linear type relationship as follows:3–6,8,10)

Effect of Woody Biomass Addition on Coke Properties

Abstract: 1) EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8603 Japan. 2) Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8603 Japan. 3) Research and Development Center, Kansai Coke and Chemicals Co., Ltd., 2-30 Ohama-cho, Amagasaki Hyogo, 660-0095 Japan. 4) Process Research Laboratories, Nippon Steel & Sumitomo Metal Corporation, 20-1 Shintomi Futtsu, Chiba, 293-8511 Japan.

Modeling of a Thermo-Electromagneto-Hydrodynamic Problem in Continuous Casting Tundish with Channel Type Induction Heating

Abstract: A mathematical model has been developed to understand the electromagnetic phenomena, heat transfer and molten steel flow in a continuous casting tundish with channel-type induction heating. Maxwell equations are first solved using the finite element method to determine the electromagnetic force and joule heating. Then, the Navier-Stokes equations and energy conservation equation are also solved with the electromagnetic force and joule heating as a source term, respectively. The two-equation RNG k-e model is used to represent the turbulent mixing. Additionally, the tracer distribution is determined by solving a scale transport equation. The coupled flow field, temperature distribution and concentration distribution are solved by the finite volume method. A non-isothermal water model experiment is performed to observe significantly buoyancy driven flow in the tundish with induction heating. The results indicate that a current loop would be formed by the induced current through the two channels. The electromagnetic force points to the center of the channel generating a pinch effect on molten steel. As skin effect and proximity effect, the electromagnetic force as well as the joule heating in the region closer to the induction coil is greater than that in another region. Therefore, spiral recirculation would occur in the channels when molten steel flows through. After flows through the channels, the molten steel lifts upward under the effect of buoyancy. The heat loss of molten steel can be compensated effectively by the joule heating, and the temperature distribution become more uniform in the continuous casting tundish with induction heating.

Structure Analysis of CaO–SiO2–Al2O3–TiO2 Slag by Molecular Dynamics Simulation and FT-IR Spectroscopy

Abstract: The structure information in the CaO-SiO2-14 mass% Al2O3–TiO2 slag was investigated by the molecular dynamics simulation and the FT-IR spectroscopy at 1 773 K. The influence of different additions of TiO2 and varying CaO/TiO2 ratios on the structure was studied to clarify the role of TiO2 in the slag. The results show that there exist three stable units, [SiO4] tetrahedron and [AlO4] tetrahedron as well as [TiO6] octahedron in the CaO-SiO2-14 mass% Al2O3–TiO2 slag. The average coordination numbers, CNSi–Al and CNAl–Al, are all approximately equal to 1 and are barely influenced by additions of TiO2 and varying CaO/TiO2 ratios, which indicates that both the [SiO4] and [AlO4] tetrahedrons are surrounded by only one [AlO4] tetrahedron and some other units. Nevertheless, [AlO4] can be linked by more than one [SiO4] tetrahedron but [SiO4] can only be surrounded by one [AlO4] tetrahedron. The bridging oxygen, classified into Si–O–Si, Al–O–Al and Si–O–Al, is preferentially localized in Si–O–Al. However, it is found a little violation of the so-called Al avoidance principle which states that the Al–O–Al linkage is absent have been obtained with about (less than) 5% Al–O–Al, and the bond of Al–O–Al is hardly affected by TiO2 additions. Replacement of CaO by TiO2 can only result in a slight change of the degree of polymerization, indicating TiO2 has the similar role as CaO to be a basic oxide.

Numerical Simulations of Inclusion Behavior and Mixing Phenomena in Gas-stirred Ladles with Different Arrangement of Tuyeres

Abstract: A CFD-PBM (Computational Fluid Dynamic-Population Balance Model) coupled model has been developed to investigate the effects of different number and position of bottom tuyeres and gas flow rate on the bubbly plume flow, inclusion removal and mixing phenomena in gas-stirred ladle. It is found that the dual blowing gives a shorter mixing time and higher inclusion removal ratio in comparison with the center blowing or eccentric blowing with one tuyere. With the increasing of separation angle of two tuyeres, the inclusion removal ratio increases, while mixing time decreases first and then increases. With the increasing of radial position of two tuyeres, the inclusion removal first increases and then decreases, and the mixing time decreases until the radial position exceeds 0.7R from the bottom center, where R is the bottom radius of ladle. It is recommended to use the two tuyeres placed at radial position of 0.6R and the angle of 135 deg in ladle to improve the joint efficiency both the inclusion removal and mixing. With the gas flow rate increasing, the efficiency both mixing and inclusion removal with the optimized tuyeres arrangement increases, however when the gas flow rate exceeds 300 NL/min in 150 ton ladle, the removal ratio and mixing time change little.

Effects of Supercooling Degree and Specimen Size on Supercooling Duration of Erythritol

Abstract: The duration of supercooling for erythritol, a promising phase change material with a melting point of 118°C, was investigated in a glass tube using three small specimen volumes of 0.025, 0.40, and 16.0 cm in glass tube diameters of 1.02, 10.0, and 27.3 mm, respectively. The supercooling duration was measured by the temperature increase of the specimen due to the release of latent heat under a constant degree of supercooling from 38 to 98°C. The supercooling duration was largely dependent on the supercooling degree and specimen sizes, and increased from approximately 0.1 to 20 000 min with a decrease in the supercooling degree and specimen size. The effects of the supercooling degree and specimen size on the supercooling duration are discussed in terms of the Johnson-Mehl-Avrami equation and three nucleation theories based on the observed solidification position; homogeneous nucleation, heterogeneous nucleation from the wall, and heterogeneous nucleation from insoluble particles.