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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 33 (1993), No. 1

  • Preface

    pp. 1-1

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    DOI:10.2355/isijinternational.33.1

  • Mathematical Expression of Slag-Metal Reactions in Steelmaking Process by Quadratic Formalism Based on the Regular Solution Model

    pp. 2-11

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    DOI:10.2355/isijinternational.33.2

    During the past three decades many theoretical treatments have been developed to predict the thermodynamic properties of silicate melts. In this paper, an attempt has been made to describe the slag-metal reactions in steelmaking process quantitatively by the relation of quadratic formalism based on the regular solution model. The approximate validity of the model was quite satisfactory to formulate the reactions of the oxygen distribution, the ferrous-ferric iron equilibrium, the manganese distribution, the phosphorus distribution and the hydroxyl capacity. The prediction of activities of components in FetO-CaO-SiO2 and FetO-MnO-SiO2 ternaries are also in good agreement with the measurements.
    x

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    1. Some Advances on the Theoretical Research of Slag ISIJ International Vol.33(1993), No.1
    2. Preface ISIJ International Vol.33(1993), No.1
    3. Kinetics of Solid Titania Reduction by Carbon in Liquid Iron ISIJ International Vol.30(1990), No.1
  • Estimation of Water Vapor Solubility in Molten Silicates by Quadratic Formalism Based on the Regular Solution Model

    pp. 12-19

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    DOI:10.2355/isijinternational.33.12

    An attempt has been made to estimate the hydroxyl capacities of some molten silicates by the regular solution model of Lumsden, which has been extensively developed to be applied to slag-metal reactions in steelmaking process by the authors. The slag systems discussed were of Na2O-SiO2, K2O-SiO2, Li2O-SiO2, CaO-SiO2 binaries and CaO-SiO2-Al2O3, CaO-SiO2-MgO, CaO-SiO2-MnO and CaO-SiO2-P2O5 ternaries. In the present work, it was assumed that the water vapor is dissolved in the slag as COH'=XHO0.5/(PH2O/P°)1/2, where, PH2O, P° are partial pressure of water vapor in the gas phase and the atmospheric pressure (Pa), respectively.
    The interaction energies between hydrogen ion and other cation i, αH-i, have been derived based on the regular solution model in the present work. As the result, it has been confirmed that the model has been applicable to predict the hydroxyl capacities over the wide range of slag composition discussed. It has been found that COH' calculated by the model showed the minimum value at the slag composition of about unit basicity. The hydroxyl capacities calculated by the model have agreed with the measured within ±0.002.
  • Some Advances on the Theoretical Research of Slag

    pp. 20-25

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    DOI:10.2355/isijinternational.33.20

    This paper is a review and a comment regarding slag models and optical basicity. It was thought to be better to establish slag model and basicity concept based on the cell structure of slag.
  • Prediction of the Thermodynamic Properties and Phase Diagrams of Silicate Systems–Evaluation of the FeO-MgO-SiO2 System

    pp. 26-35

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    DOI:10.2355/isijinternational.33.26

    Molten silicates are ordered solutions whose excess Gibbs energies cannot be well represented by the usual polynomial representation of deviations from ideal solution behavior. An adaptation of quasichemical theory has been proposed which is capable of describing the properties of ordered solutions and of representing the measured properties of binary silicates over broad ranges of composition and temperatures. For simple silicates such as the MgO-FeO-SiO2 ternary system in which silica is the only acid component, a combining rule generally leads to good predictions of the thermodynamic properties of ternary (and probably higher order) solutions from those of the binaries. In basic solutions, these predictions are consistent with those of the Conformal Ionic Solution Theory. Our results indicate that our approach could provide a potentially powerful tool for representing and predicting the thermodynamic properties of multicomponent molten silicates. A complete critical evaluation of the thermodynamic properties and phase diagrams of the FeO-MgO, FeO-SiO2, MgO-SiO2 and FeO-MgO-SiO2 systems is presented in which the modified quasichemical model is used for the liquid phase. Optimized equations for the thermodynamic properties of all phases are obtained which reproduce all thermodynamic and phase diagram data to within experimental error limits from 25°C to liquidus temperatures at all compositions. The optimized thermodynamic properties and phase diagrams are the best estimates presently available.
    x

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    1. Determination of Activities in Slags Containing Chromium Oxides ISIJ International Vol.33(1993), No.1
    2. Surface Tensions and Densities of Molten Al2O3, Ti2O3, V2O5 and Nb2O5 ISIJ International Vol.33(1993), No.1
    3. Redox Equilibria in Al2O3-CaO-FeOx-SiO2 and Al2O3-CaO-FeOx-MgO-SiO2 Slags ISIJ International Vol.33(1993), No.1
  • Sulphide Capacities of CaO-Al2O3-MgO and CaO-Al2O3-SiO2 Slags

    pp. 36-42

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    DOI:10.2355/isijinternational.33.36

    The sulphide capacities of CaO-Al2-Al3, CaO-Al2O3-MgO and CaO-Al2O3-SiO2 slags were studied at 1823 to 1923 K to estimate the sulphur distribtion ratio between secondary steelmaking slag and liquid steel.
    From the obtained results, it was confirmed that substitution of MgO or SiO2 for CaO at a given NAl2O3 decreased the sulphide capacities in both systems of CaO=Al2O3-MgO and CaO-Al2O3-SiO2. The evaluated maximum values of sulphide distribution ratio for both slags were higher than 1000 at 1873 K on the condition of CaO-saturation if the dissolved aluminium content in steel was assumed to be 0.01 mass%.
  • Effects of CaO, MnO, MgO and Al2O3 on the Sulfide Capacities of Na2O-SiO2 Slags

    pp. 43-47

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    DOI:10.2355/isijinternational.33.43

    As a fundamental study on the thermodynamic properties of Na2O-based slags, the sulfide capacities of the Na2O-SiO2 slags with and without CaO, MnO, MgO, or Al2O3 were measured at 1500°C by conducting a method of gas/slag equilibration, and the effects of CaO, MnO, MgO, and Al2O3 on the sulfide capacities of Na2O-SiO2 slags were investigated in connection with slag basicity.
    The results show that the additive oxides of CaO, MnO, and MgO increase the sulfide capacities of Na2O-SiO2 slags, but that of Al2O3 decreases it. From the evaluation of these contributions the sulfide capacities of Na2O-SiO2 slags can be expressed as a function of the modified slag basicity B' as follows.
    logCS=4.64B'–6.88 (1500°C)
    B'={(Na2O)+m(MO)}/{(SiO2)+m'(MO')} [mole ratio]
    m=0.7 for MO=CaO, 0.4 for MnO, 0.3 for MgO
    m'=0.5 for MO'=Al2O3.In addition, the relation between sulfide capacity and theoretical optical basicity for Na2O-SiO2 slags was also investigated in comparison with that for CaO-based slags. As a result, the present correlation can be expressed by logCS=27.0Λth–21.2 (1500°C)
    and is not in agreement with that previously developed for CaO-based slags.
    x

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    1. Sulphide Capacities of CaO-Al2O3-MgO and CaO-Al2O3-SiO2 Slags ISIJ International Vol.33(1993), No.1
  • The Solubility of Nitrogen in the CaO-CaF2-Al2O3 System and Its Relationship with Basicity

    pp. 48-52

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    DOI:10.2355/isijinternational.33.48

    Nitrogen solubility in its different forms has been determined for the CaO-CaF2-Al2O3 system at 1773 K. Carbonate ions solubility has also been determined for the same temperature. Free incorporated nitride depend on the slag structure and its interaction with other cations. It is shown that nitrogen solubility does not depend on the activity of a single component. Flourine ions behave in a similar way as the do in the ternary silicate system CaO-CaF2-SiO2, liberating both oxygens and incorporated nitride from the networks. The effect of addition of silica, titania and barium chloride to the system on nitrogen solubility has been determined.
    x

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    1. Effect of CaF2 Addition on the Viscosity and Structure of CaO–SiO2–MnO Slags ISIJ International Vol.53(2013), No.6
  • Phosphorus Partition between CaOsatd.-BaO-SiO2-FetO Slags and Liquid Iron at 1873 K

    pp. 53-58

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    DOI:10.2355/isijinternational.33.53

    Unconventional, highly basic slags such as CaO bearing slags are to be used for producing high quality steel. The purpose of this study is to find out what the thermodynamic properties of CaOsatd.-BaO-SiO2-FetO slags are at steelmaking temperatures. The phosphorus partition between CaOsatd.-BaO-SiO2-FetO slags and liquid iron was measured as a function of slag composition, together with the CaO solubility. The phosphate capacity of the present system at 1873 K ranged from 1017.3 to 1020.0. BaO has been observed to be more effective than CaO for dephosphorization of steel in a thermodynamic sense. The activity coefficients of FeO and FeO1.5 have been measured and discussed in terms of the stability of orthosilicates. The FeOn(2n-3)- anion is likely to be a species of iron in the CaOsatd.-BaO-SiO2-FetO system, judging from the measurement of Fe3+/Fe2+ ratio.
  • Thermodynamic Aspects of Na2O and CaF2 Containing Lime-based Slags Used for the Desulphurization of Hot-metal

    pp. 59-65

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    DOI:10.2355/isijinternational.33.59

    Sulphur distribution ratios have been determined between carbon-saturated iron and Na2O-SiO2, Na2O-SiO2-CaO and Na2O-SiO2-CaO-CaF2 slags at 1350°C. The experiments were performed in graphite crucibles under a carbon monoxide atmosphere. Sulphide capacities were calculated based on the sulphur distribution ratios. Additions of Na2O increase the sulphide capacity of silicate as well as lime-based slags significantly and the Na2O-equivalent of CaO was determined as 0.30. CaO-Na2O-SiO2-CaF2 slags possess high sulphide capacities as well as low melting points, and can consequently be utilized for hot-metal treatment at relatively low temperatures. However, additions of CaF2 decrease the sulphide capacity of these slags and consequently only enough CaF2 should be used to ensure that the slags remain liquid during the desulphurization treatment.
  • Determination of Activities in Slags Containing Chromium Oxides

    pp. 66-74

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    DOI:10.2355/isijinternational.33.66

    Activities of CrO and CrO1.5 were determined in slags based on the systems of CaO-SiO2-CrOx, CaO-SiO2-MgO-CrOx, CaO-SiO2-Al2O3-CrOx, and CaO-SiO2-MgO-Al2O3-CrOx with electro-motive force method. Equilibrium was achieved between Cr-saturated CrAg alloy and slags. Effects of temperature and slag composition on the activities of chromium oxides and the oxidation state of chromium in the slags were investigated. Chromium oxides activities decreased but the divalent chromium fraction in the slags increased when elevating temperature in the range of 1500-1600°C. The slag basicity has a significant effect, the higher the slag basicity, the higher the activities of chromium oxides, and the lower the divalent chromium fraction. By partial substituting MgO for CaO, activities of CrO and CrO1.5 will decrease, but the effect on the oxidation state of chromium in the slag is not obvious. Increasing Al2O3 content from 0 to 10 mol% results in higher activities of chromium oxides and lower divalent chromium fraction. Further increasing of Al2O3 content to 20 mol% does not cause any significant effect. In addition, activities of chromium oxides and oxidation state of chromium in a FeCr type slag system were examined.
  • An Equation for Vapor Pressure and Its Application to Molten Salts

    pp. 75-78

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    DOI:10.2355/isijinternational.33.75

    An equation for the vapor pressure of molten salts has been derived by combining the formula based on the harmonic oscillator model of a liquid with the modified Lindemann's equation proposed previously by one of the authors, as follows:
    p=4.2×1013σ3/2T-1/2exp(-ΔHV/NkT)
    where p is the vapor pressure, σ the surface tension, ΔHV the enthalpy of evaporation, T the absolute temperature, N Avogadro's number, and k Boltzmann's constant.
    The values of the enthalpy of evaporation for various molten salts have been calculated from this equation using the experimental values of surface tension. The calculated values agreed well with experimental data within ±10%.
  • Thermodynamics of Phase Separation between Molten Metal and Slag, Flux and their Process Implications

    pp. 79-87

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    DOI:10.2355/isijinternational.33.79

    Most metallurgical processes are consisting of two essential steps of chemical reaction followed by phase separation. When the process is in equilibrium, the both steps can be evaluated based upon thermodynamic data. To explain the principle of phase separation, systems related to practical smeltings such as slag-metal or slag-matte was reduced into ternary system and ternary phase equilibria were derived from binary data based upon the regular solution model. The special interest is focussed to the fact that ternary phase separation tendency is observed between a neutral component and a strong intermediate compound even though all the constituent binary systems have miscible trends.
    The experimental results on the oxidic dissolution of valuable metals in the binary and ternary slags in FeOx-SiO2-CaO system are reasonably explained by taking into account the immiscible trend between MO and xBO·AO in a ternary MO-AO-BO (metal oxide-acidic oxide-basic oxide) system. The behavior of activity or activity coefficient of metal oxide derived by the regular solution model is compared with the experimental results obtained for SnO, CuO0.5 and PbO.
    The experimentally determined ternary miscibility gaps for the systems Cu-Pb-As, Cu-Pb-Sb, Sn-Fe-Si and Sb-Fe-S are explained thermodynamically, and it is recognized that the basic principles of a few smelting processes for lead, tin and antimony are reasonably explained by these ternary miscibility gaps. Through these examples, it is suggested, in principle, that the process of metal extraction can be designed thermodynamically.
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    1. Wettability between Molten Slag and MgO–C Refractories for the Slag Splashing Process ISIJ International Vol.53(2013), No.4
    2. Preface ISIJ International Vol.33(1993), No.1
    3. Determination of Activities in Slags Containing Chromium Oxides ISIJ International Vol.33(1993), No.1
  • Microanalytical Investigations of Oxidizing Slags with Special Consideration of Phosphorus- and Sulphur-containing Phases

    pp. 88-97

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    DOI:10.2355/isijinternational.33.88

    The necessity to minimize the slag volume, to adjust the phosphorus content in the steel as low as possible and to utilize the converter slag, as far as possible, also for desulphurization requires an efficient slagging practice. This paper presents results of investigations on solidified converter and laboratory slags obtained with the microanalyzer. The factor responsible for the binding of phosphorus in converter slags is the formation of dicalcium silicate, whereas for the binding of sulphur it is dicalcium ferrite.
    In slags from laboratory melts with an SiO2-content below 1 wt% phosphorus is detected in a separate calcium phosphate phase. The negative effects on metallurgical results caused by higher contents of MgO and Al2O3 in converter slags are described on the basis of an interpretation of evaluations from large-scale tests. The sequence of dephosphorization and desulphurization in the converter process is discussed with the aid of the ionic theory of slags.
    x

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    1. Surface Tensions and Densities of Molten Al2O3, Ti2O3, V2O5 and Nb2O5 ISIJ International Vol.33(1993), No.1
    2. Redox Equilibria in Al2O3-CaO-FeOx-SiO2 and Al2O3-CaO-FeOx-MgO-SiO2 Slags ISIJ International Vol.33(1993), No.1
    3. The Kinetics of Reduction of MnO in Molten Slag with Carbon Saturated Liquid Iron ISIJ International Vol.33(1993), No.1
  • Manganese Reaction Rate in Combined Blowing Converter with Less Slag

    pp. 98-103

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    DOI:10.2355/isijinternational.33.98

    Manganese behaviors under oxygen gas blowing are investigated in the 50 kg combined blowing converter and 250 t combined blowing converter. Manganese reaction mechanism is discussed and reaction rate model is established. Rate parameters in the model were discussed. Using the rate model, manganese contents at latter period and the end of operations were estimated. The accuracy of the estimation is good and proved the possibility of operational use.
  • The Kinetics of Reduction of MnO in Molten Slag with Carbon Saturated Liquid Iron

    pp. 104-108

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    DOI:10.2355/isijinternational.33.104

    This investigation devotes to the kinetics of the reduction of (MnO) with carbon-saturated liquid iron. The experiment condition involves high content realm of both (%MnO) and %Mn. It was found that the reduction is limited by the interfacial reaction. By means of a X-TV dynamic metallurgical phenomena displaying device, the slag-iron interface was proved to be the essential site for evolving the reduction product CO. The content variation of surface active agent S affects obviously on the reduction rate. If no carbon is added in slag, then a hump emerges on the curve of (%FeO) vs. reaction time. In this case, the apparent reaction order is 2. If there is a carbon addition in slag, the process is of apparent first order. Based on the three step model of reactions in series, the aforementioned phenomena and regularities were elucidated unitedly.
  • Effects of Both Flux Compositions and Oxidizing Conditions on the Dephosphorization of High-chromium Hot Metal by Using CaO-CaF2 Based Fluxes

    pp. 109-115

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    DOI:10.2355/isijinternational.33.109

    Owing to the spread of using coke for melting of stainless steel scrap and smelting reduction of chromium ore in the stainless steel production, it is thought that the development of an inexpensive and effective method of dephosphorization of chromium-containing hot metal is a necessity. In this study, the dephosphorization was investigated by a method of injecting the powder mixtures of lime and fluorspar with the carrier gas containing oxygen into chromium-containing hot metal. The results show clearly that even with about 30 mass% of chromium content, effective dephosphorization is possible. A powder mixing ratio of lime to fluorspar of 1/1 by weight has been found to be favorable, and under optimum oxidation conditions, chromium oxidation loss has been kept at 0.1 mass% or below at the chromium content of about 30 mass%. Finally, from a thermodynamic viewpoint, the oxygen potential of the dephosphorization with high chromium content levels has been considered to be determined by the formation reaction of CaO·Cr2O3.
  • Kinetic Behavior of Dissolution of Sintered Alumina into CaO-SiO2-Al2O3 Slags

    pp. 116-123

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    DOI:10.2355/isijinternational.33.116

    The effects of revolution speed, temperature and slag composition on the dissolution rate of sintered alumina into molten CaO-SiO2-Al2O3 slags were examined by the rotating cylinder method. The slags used had 10% Al2O3 and CaO/SiO2 ratios of 0.64 to 1.25.
    The dissolution rate of alumina into CaO-SiO2-Al2O3 slags increased with increasing revolution speed and rising temperture. It was concluded from these results that the dissolution rate was controlled by mass transport in the slag boundary layer. The dissolution rate of alumina also increased with increasing CaO/SiO2 and an abrupt increase was observed in the vicinity of CaO/SiO2=1.
    The addition of 15% NaF or CaF2 to slags with CaO/SiO2 ratio of 0.80 to 1.25 increased the dissolution rate by a factor of 2 to 6 compared with those of CaO-SiO2-Al2O3 slags. Such an increase of the dissolution rate is estimated to be caused mainly by the increase of mass transport coefficient.
    The penetration of slag components, CaO and SiO2, into an alumina cylinder was observed in all experiments. Besides, CaO·6Al2O3 compound was formed in the slag penetration layer for CaO-SiO2-Al2O3 slags with CaO/SiO2≥1.
  • The Characteristics and the Function of a Thick Slag Layer in the Smelting Reduction Process

    pp. 124-132

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    DOI:10.2355/isijinternational.33.124

    The characteristics of the slag layer in smelting reduction with a large amount of slag were examined with various devices, and its influence on the operation performance was investigated.
    (1) The characteristics of slag layer. The average density of the slag layer calculated by the detected slag height was 0.6-1.1 t/m3. In the practical smelting reduction condition, the average density of slag layer seems to be 0.8-1.0 t/m3. The temperature difference between the slag layer and the metal bath was 30°C or less. The amount of metal droplets in the lower 30 vol% of the slag layer reaches 30 wt% or more. In the upper 70 vol% of the slag layer, it depends on the stirring intensity of metal bath and slag compositions. 85-95 wt% of these originated in the stirred metal bath according to the tracer test.
    By combining the sampling test and the calculation using measured data, the distribution of carbonaceous materials in the slag layer could be obtained.
    (2) The influence of the characteristics of slag layer on the operation performance: The increase of metal droplets in the slag layer decreases post combustion and increases iron dust generation. The increase of the amount of slag decreases the generation of iron dust and carbon dust. When coal is used instead of coke, the carbon content of the metal bath decreases. This phenomenon was explained by the distribution of carbonaceous materials and metal droplets in the slag layer.
    The principle for the simultaneous achievement of high post combustion, acceleration of reduction and heat transfer, suppression of dust generation, and the adjustment of carbon content of metal bath by controlling the distribution of metal droplets and carbonaceous materials in slag layer is shown.
  • Transport Phenomena of Oxygen through Molten CaO-SiO2 System Containing Zinc and/or Nickel Oxide

    pp. 133-139

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    DOI:10.2355/isijinternational.33.133

    Oxygen transfer rates, P, through molten NiO-CaO-SiO2, ZnO-CaO-SiO2 and NiO-ZnO-CaO-SiO2 systems were observed by using a molten thin film penetration method developed by the author. Observation temperature were about 1450, 1500 and 1550°C.
    Magnitudes of the transfer rate are 1 to 5 times 10-8 mol O2·cm-1·s-1, the same magnitude as that in the iron oxide-CaO-SiO2 system measured previously. In the system containing NiO, the greater NiO content, the higher the oxygen transfer rate. In the system containing ZnO, in contrast, the greater the ZnO content, the higher the oxygen transfer rate in the case of less than 20 mol% ZnO and the lower the oxygen transfer rate in the case of more than 20 mol% ZnO.
    Effects of constituents on oxygen transfer rate, P, in mol O2·cm-1·s-1 are empirically expressed as follows:
    A system less than 12.5 mol% NiO:
    P=3.15×10-9(mol%NiO)
    A system less than 35 mol% ZnO:
    P=–8.5×10-11(mol%ZnO-22)2+4.2×10-8
    Temperature dependencies of the oxygen transfer rates are:
    7.5mol%NiO-46.3mol%CaO-46.3mol%SiO2;
    P=3.51×10-2exp(-25.3×103/T)
    10mol%ZnO-45mol%CaO-45mol%SiO2;
    P=3.24×10-2exp(-25.3×103/T)
    20mol%ZnO-40mol%CaO-40mol%SiO2;
    P=6.39×10-2exp(-25.3×103/T)
    30mol%ZnO-35mol%CaO-35mol%SiO2;
    P=4.96×10-2exp(-25.3×103/T)
    It is speculated that NiO and ZnO act as p- and n-type semiconductors, respectively, on the basis of the discussion of the dependency of the transfer rate on oxygen partial pressure at the surface of molten oxide.
  • Heat Transfer between Mold and Strand through Mold Flux Film in Continuous Casting of Steel

    pp. 140-147

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    DOI:10.2355/isijinternational.33.140

    Laboratory experiments have been performed to make clear heat transfer behavior in the mold of continuous casting of steel. The overall thermal resistance of a parallel-sided plate filled with mold flux has been measured. The interfacial thermal resistance between the mold and flux film interface and the thermal conductivity of the mold flux are analyzed quantitatively. An interfacial thermal resistance corresponding to the air gap of 20-50 μm is observed in the case of solid mold flux. When the temperature of the mold surface exceeds solidification temperature of the flux, the interfacial thermal resistance disappears together with disappearance of air gaps. The crystallization of the mold flux inhibits the radiative heat transfer that is equivalent to 20% in the total heat flux. The thermal conductivity of the mold flux depends on the size of silicate ions. Large size of silicate ion promotes the conductive heat transfer.
    x

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    1. Prediction of the Thermodynamic Properties and Phase Diagrams of Silicate Systems–Evaluation of the FeO-MgO-SiO2 System ISIJ International Vol.33(1993), No.1
  • The Influence of Structure on the Physico-chemical Properties of Slags

    pp. 148-155

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    DOI:10.2355/isijinternational.33.148

    The current knowledge of the structures of silicate slags is summarised and the relationships between measures of the depolymerisation of the melt and various physical properties are examined. It is shown that the optical basicity when corrected for the cations required to charge-balance any AlO45- tetrahedra present, provides a reasonable measure of the depolymerisation of the melt and has the advantage over the (NBO/T) ratio that it compensates for cation effects. It is shown that the depolymerisation of the melt is the primary factor affecting most physical properties, the cations having only a secondary effect. The relationships between structure and the viscosity, electrical and thermal conductivity, diffusion coefficient, density, thermal expansion coefficient, thermodynamic and optical properties of melts are discussed.
    x

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    1. Redox Equilibria in Al2O3-CaO-FeOx-SiO2 and Al2O3-CaO-FeOx-MgO-SiO2 Slags ISIJ International Vol.33(1993), No.1
    2. Surface Tensions and Densities of Molten Al2O3, Ti2O3, V2O5 and Nb2O5 ISIJ International Vol.33(1993), No.1
    3. The Effect of Aluminium Content on Thermophysical Properties of Ni-based Superalloys ISIJ International Vol.46(2006), No.1
  • Surface Tensions and Densities of Molten Al2O3, Ti2O3, V2O5 and Nb2O5

    pp. 156-165

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    DOI:10.2355/isijinternational.33.156

    Surface tensions and densities of molten Al2O3, Ti2O3, V2O5 and Nb2O5 were determined accurately by the maximum bubble pressure method. The measurements were carried out under Ar+10%H2 for molten Al2O3 and Ti2O3, and under air for molten V2O5 and Nb2O5. Surface tension and density of molten Al2O3 near the melting point are 606±6 mN m-1 and 3.06±0.03×103 kg m-3, and those of molten Ti2O3 are 584±5 mN m-1 and 3.91±0.03×103 kg m-3, respectively. The temperature coefficient of surface tension of molten V2O5 is slightly positive value of 0.0111 mN m-1 K-1, while for molten Nb2O5 it is negative value of -0.0596 mN m-1 K-1. This suggests that the network structure of molten V2O5 changes with temperature. The temperature coefficient of density of molten V2O5 is very low. The results are discussed in comparison with those of other molten pure oxides and fluorides having high melting points.
  • Observations on the Role of Interfacial Phenomena in Materials Processing

    pp. 166-175

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    DOI:10.2355/isijinternational.33.166

    Examples of the role interfacial phenomena can play in materials processing are highlighted in the description of a number of recent research studies conducted at Imperial College. Interfacial phenomena play critical roles in increasing or retarding the rates of chemical reaction and in promoting or hindering wetting and dispersion of phases in each other.
    The reduction of ilmentite to iron and titanium carbide or titanium oxycarbide has been studied with the ultimate aim of achieving separation of the titanium and its subsequent conversion to pigment grade titanium dioxide. The need to achieve good separation of iron from other reaction products is then a prime concern. The effects of reducing conditions on the wetting of titanium carbides and oxycarbides by iron alloys has therefore been studied. It seems that associative adsorption of titanium and carbon may be responsible for the observed effects of dissolved titanium and carbon on the wetting of TiC by liquid iron alloys.
    As a result of this work a further project has been generated involving the identification of conditions for achieving good dispersions of refractory carbides including titanium carbide in iron alloys. The major motivation behind this work was the desire to develop a cheap casting based process for the production of iron based metal matrix composites capable of producing near net shape products. As a result of this work a novel rapid testing technique for the assessment of the wettability and compatibility of potential filler materials with liquid metal matrices has been developed. The technique employs levitation and quenching of liquid metal drops containing added filler materials to permit assessment of alloy composition, filler coatings and temperature on matrix/filler interactions. The levitation technique has been further utilised in a study of the conditions required for dispersion or non dispersion of second phase particles in liquid superalloys. In this case the cleanliness of the superalloys achieved during recycling procedures is determined by the ease with wich inclusions can be removed. Some observations with ternary oxides also indicate the importance of the associative adsorption phenomenon.
    The importance of interfacial considerations has also been highlighted by our studies on the production of aluminium-titanium-boron grain refining master alloys from fluoride fluxes. Entrapment of the products can result from emulsification occurring during the reduction reactions. A detailed study of this phenomenon has been conducted using a modified sessile drop technique. The results obtained indicate the critical role that interfacial tension plays in determining the ease of metal-flux separations and in determining whether products are dispersed in the metal or slag.
    The kinetics of metal-salt reactions were also found to be of importance. Fast transfer of Ti and B to the metal results in the build up to TiAl3. TiB2 or AlB12 at the interface. These compounds when present at the interface can be wet by the flux and result in emulsion formation. Inhibition of emulsification can be achieved by the presence of surface active elements such as magnesium and calcium.
    The role of interfacial phenomena in influencing the kinetics of the reduction of slags has been studied in an investigation of the kinetics of alkali metal oxide release from silicate melts. The kinetics of K2O and Na2O release during heating in graphite crucibles has been studied from binary alkali oxide-silicon dioxide melts and from a wide range of CaO-Al2O3-SiO2 slags. The contribution of the wetting of the graphite by the slag towards influencing reaction kinetics represents a notable feature of the study.
  • Viscoelastic Properties of Molten ZnCl2-MCl (M: Na, K) Binary Systems

    pp. 176-181

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    DOI:10.2355/isijinternational.33.176

    In order to clarify the viscoelastic properties of ZnCl2-MCl (M: Na, K) binary melts, hypersonic velocities have been measured in the temperature range covering about 150 K above the liquidus temperatures of the melts over the composition range of 0 to 50 mol% MCl by means of the Brillouin scattering method. Absorption coefficients of ultrasound were measured for molten ZnCl2 at the frequency range of 5-55 MHz. The hypersonic velocity of ZnCl2 decreases linearly with increasing temperature at the high and the low temperature regions, but at the intermediate temperature region, shows a curvilinear temperature dependence, indicating dispersion of sound propagation.
    The dispersion behavior observed is well described in terms of the single relaxation theory. It was found that the relaxation frequency of the binary melts increases steeply with an addition of MCl. This is considered to be due to the depolymerization of the network structures in the melts.
  • Infrared Emission Spectra of a Thin Film of Molten Alkali-metal Nitrates

    pp. 182-187

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    DOI:10.2355/isijinternational.33.182

    A hot thermocouple technique was applied to measure the emission spectra of a thin film of molten nitrates. The thickness of the sample must be less than one micro meter to obtain a reasonable spectrum. Spectra obtained for various nitrates were the sharpest of the kinds and agreed with those measured by the conventional complicated technique. The shifts of the absorbance were observed by changing the cation and these could be correlated by the Pauling's ionic radii of the cations. The correlation was similar to those reported for the molten carbonate.
  • Structural Analysis of Na2O-B2O3 Melts by Pulsed Neutron Total Scattering Method and Molecular Dynamics Simulation

    pp. 188-194

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    DOI:10.2355/isijinternational.33.188

    In order to obtain direct information on the structure of sodium borate melts which are of use in metallurgical processes, pulsed neutron total scattering measurements have been carried out on 10mol%Na2O- and 30mol%Na2O-B2O3 melts at 1073 K, in addition to the previous measurement on pure B2O3 melt. Molecular dynamics (MD) calculations have also been made on pure B2O3 and 30mol%Na2O-B2O3 melts at 1073 K.
    With increase in Na2O content, the first peak of RDF(r), representing B-O correlation, spread asymmetrically to larger r side, and the coordination number of O atoms around a reference B atom nB-O increased from 3.0 to 3.5, showing variation of B-O correlation. This increase in nB-O could be explained by the simple assumption that two BO3 triangle structure units are converted to two BO4 tetrahedron structure units with the addition of one Na2O molecule in the same way as in Na2O-B2O3 glasses. These nB-O values also agreed well with those obtained by MD calculations, which showed the clear evidence of the appearance of BO4 units that the distribution of O-B-O bond angle spread from 120° to smaller angle side for 30mol%Na2O-B2O3.
    From these results, it is safely concluded that a part of BO3 triangle structure units converted to BO4 tetrahedron structure units with the addition of Na2O up to 30 mol% to B2O3 melt in the same way as in Na2O-B2O3 glasses.
    x

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  • Redox Equilibria in Al2O3-CaO-FeOx-SiO2 and Al2O3-CaO-FeOx-MgO-SiO2 Slags

    pp. 195-203

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    DOI:10.2355/isijinternational.33.195

    Measurements of the Fe3+/Fe2+ ratio in Al2O3-CaO-FeOx-SiO2 and Al2O3-CaO-FeOx-MgO-SiO2 slags in equilibrium with Ar-CO-CO2 gas mixtures have been made in the temperature range of 1400 to 1500°C and oxygen potentials between 3×10-9 and 10-5 atm. The results from these experiments indicate that in Al2O3-CaO-FeOx-SiO2 slags with 0-10 wt% MgO, the ratio of activity coefficients of ferrous oxide to that of ferric oxide decreases sharply as the total iron oxide content increases from about 0.8 to 3 wt%. However, at total iron contents of greater than 6 wt% the ratio of the activity coefficients of iron oxides becomes virtually independent of the iron content of the slag.
  • Limitations in the Metallurgical Application of Optical Basicity

    pp. 204-209

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    DOI:10.2355/isijinternational.33.204

    Basicity is a useful concept in metal processing inspite of its uncertain theoretical basis. The unlimited application of basicity in metallurgical systems, however, results in confusion of the basicity concept.
    After a short review on the basicity of metallurgical slags was done in the present study, optical basicities in some pure oxides and two phase glases in alkaline borate systems measured by the photoacoustic spectroscopy are reported. Two optical basicity values were obtained in the two phase regions of the borate glasses. It is suggested that basicity can not work usefully in such extreme composition regions and that limitations in basicity should be considered in its metallurgical application.
  • Applicability of Molecular Dynamics to Analyses of Refining Slags

    pp. 210-217

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    DOI:10.2355/isijinternational.33.210

    By the use of molecular dynamics simulation (MD), varieties of properties including structural, transport, optical and thermodynamic properties can be calculated. Since this feature is very attractive to the analyses of refining slags, its applicability was studied. CaO-SiO2 melts with CaO contents ranging from 40 to 60 at% were simulated at 1873 K. The calculated pair distribution functions and general tendency of silicon ion fractions with various number of non-bridging oxygen ions agreed well with experiments reported elsewhere. The calculated diffusion coefficient of every ion as a function of CaO content was also in good agreement with the measured values. These demonstrate the promising applicability of MD to slag analyses.
    The melt of 45at%CaO-45at%SiO2-10at%CaF2 was also simulated by MD to study the effects of fluorine addition to silicate melt. The hypothesis of the existence of di-fluorine ions in some thermodynamic modeling of slags was not verified due to the lack of appropriateness of the interatomic potentials used in this study.
  • Effect of Reflected Wave from the Wall of a Vessel and End Effect of the Plate in the Oscillating-plate Method

    pp. 218-223

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    DOI:10.2355/isijinternational.33.218

    The effect of reflected wave and the end effect of a new oscillating-plate viscometer, constructed by Sasahara et al., have been investigated experimentally over a wide range of viscosity. The results obtained are as follows:
    (1) The resonant frequencies of the plate oscillations in liquid samples decrease with increasing ρμ values. However, the viscosity dependence of the resonant frequency is negligibly small when an adequate leaf-spring is used for chinning the plate attached to stem.
    (2) The effect of reflected wave from the wall of a vessel is negligible when the distance between the plate and wall is kept over one wavelength of the wave produced by the plate oscillations.
    (3) The end effect of the oscillating-plate increases with increasing not only the thickness of the plates but also the viscosity of liquids.
    (4) The working formula for viscosity determination by the oscillating-plate method should be corrected by considering the above two effects.
  • Physical Model of Slag Foaming

    pp. 224-232

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    DOI:10.2355/isijinternational.33.224

    Physical model of slag foaming was developed by using results of cold and hot model experiments. The bubble size at the slag/metal interface, the void fraction of foam and the film life of a bubble at the top surface of slag were calculated. The governing factors of slag foaming have been clarified with this model. It was confirmed that the bubble size at the slag/metal interface is determined basically by the static balance between the buoyancy force and the adhesive force to the slag/metal interface. It was resulted that the slag/metal interfacial tension and the surface tension of metal also affect the foam height besides the surface tension and the viscosity of slag because they change the bubble size.
  • Critical Cooling Rates for the Formation of Glass for Silicate Melts

    pp. 233-238

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    DOI:10.2355/isijinternational.33.233

    The critical cooling rate required for the formation of glass is one of the important characteristics for silicate slag. The critical cooling rates have been measured for R2O (R=Li, Na and K)-SiO2 and R'O (R'=Ca, Sr and Ba)-SiO2 systems by the combined use of the hot-thermocouple method and an ordinary melt-quenching method. In all systems, the minima in critical cooling rate corresponded with the composition range of low liquidus temperatures near the eutectics; the critical cooling rates decreased with increasing viscosities at the liquidus temperatures. The measured critical cooling rates were similar to those predicted by the Uhlmann equation and Ota equation. Some factors affecting the critical cooling rate were discussed.

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