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

ISIJ International Vol. 32 (1992), No. 10

  • Positioning Coke Particles in Iron Ore Sintering

    pp. 1047-1057

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    DOI:10.2355/isijinternational.32.1047

    Coke is the most widely used solid fuel in iron ore sintering. Generally coke is blended with the other sinter mix components dry before granulation. Several studies in the literature have shown that, in addition to the properties of coke, e.g., size distribution, the delayed introduction of coke into the sinter mix, e.g., added towards the discharge end of the granulation drum, affected sintering and the sinter quality parameters. This study was initiated with the view to determine if the granulation practice at the sinter plant of The Broken Hill Proprietary Co., Ltd. (BHP), Rod and Bar Products Division (RBPD) could be altered to improve the positioning of coke in the granulated sinter mix. As pilot-scale sintering studies did not indicate positive results, further studies were carried out including the use of longer granulation time, and the use of optical microscopy to characterise the structure of the formed granules. Results showed that the positioning of the finer coke particles depended on when the coke was introduced into the granulating mix. In contrast, the large coke particles remained free, i.e., unattached to other materials, regardless of the coke addition technique. When the fine coke particles were well-embedded into granules their combustion rate was decreased; this broadened the width of the coke combustion zone resulting in lower sinter productivity.
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  • Production Test of High-carbon Ferrochrome Using a Shaft Furnace with Coke Packed Bed Injected with Oxygen and a Large Quantity of Pulverized Coal

    pp. 1058-1065

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    DOI:10.2355/isijinternational.32.1058

    High-carbon ferrochrome has been produced by electric arc furnace, but its production cost is very high because of the high electricity cost in Japan. So, for the purpose of decreasing its production cost, experiments of high-carbon ferrochrome production (production rate=50-110 kg/h) were performed using an experimental melting furnace with coke packed bed injected with oxygen and a large quantity of pulverized coal and following results were obtained.
    (1) In the experimental plant, high-carbon ferrochrome of [Cr]=40-60% was produced by this process.
    (2) It was confirmed that sintering of chromium ore had the effects to improve the characteristics of the reduction and melt down of chromium ore and the favorable characteristics of chromium ore sinter were cleared as follows: CaO/SiO2=1.0-1.3, slag rate=1100-1300 kg/t-(Cr+Fe).
    (3) It was confirmed that the fuel rate and productivity could be improved under the stable operation by using the chromium ore sinter as a material.
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    1. Mechanisms of Hanging Caused by Dust in a Shaft Furnace ISIJ International Vol.31(1991), No.9
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    3. Suppression of the Formation of Large Pores in the Assimilated Parts of Sinter Produced Using Pisolitic Ores ISIJ International Vol.36(1996), No.11
  • Influence of Gaseous Sulfur on Hydrogen Reduction of Wustite Added with Foreign Oxides

    pp. 1066-1075

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    DOI:10.2355/isijinternational.32.1066

    Dense wustite plates added separately with major gangues in ironmaking were reduced using a thermobalance at 900°C with H2-H2O-H2S mixtures to elucidate the coexisting influence of each added oxide and gaseous sulfur on the reduction behavior.
    In the tests without sulfur, the reduction was retarded by the existence of Al2O3 as well as MgO in wustite mostly by the formation of dense iron in porous wustite (B type iron), while it was enhanced by adding CaO or SiO2 with porous iron (A type iron). These results coincided with several earlier works.
    The tests with as=0.01 as the sulfur activity in gas phase, which was defined relative to Fe/FeS equilibrium, showed that their reduction behavior did not change significantly compared with those without sulfur. However, with increasing as up to 0.10 most of the reduction rates tended to approach a moderate level regardless of adding above oxides, being affected by the reducing potential and the two cases whether traces of oxysulfides are formed in Fe/FeO interface or not. In the former case, coarse iron morphology (AC or FC type iron, C; coarse, F; fibrous) was observed with relatively less reduction rates than the latter, in which fine morphology (A or F type iron) was realized except the case of Al2O3 (B type iron) to eliminate the extreme reduction retardation. Only under the coexistence of sulfur at as=0.10 and CaO, F type morphology was predominated.
    These reduction behavior is discussed focusing a few actions caused by gaseous sulfur.
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  • Thermodynamics of Reducing Dephosphorization of Manganese and Manganese Ferroalloys

    pp. 1076-1080

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    DOI:10.2355/isijinternational.32.1076

    Thermodynamic conditions of dephosphorization of manganese and its ferroalloys with calcium containing fluxes have been analyzed with the help of experimental data on the thermodynamic properties of Mn-P and Ca-P alloys obtained earlier. Equilibrium coefficients of phosphorus distribution between liquid manganese and slag have been calculated. An influence of oxygen and nitrogen partial pressures in the reaction zone on dephosphorization has been established.
  • The Kinetics of Desulfurization of Hot Metal by CaO-CaF2 Based Fluxes

    pp. 1081-1083

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    DOI:10.2355/isijinternational.32.1081

    A kinetic model, which considers the effect of transitory reaction and permanent-contact reaction on sulfur removal rate, as in the case of using CaO-CaF2 based fluxes powder injection to desulfurize hot metal containing vanadium of 0.34% and sulfur content of 0.08% is developed in the present work. Some important factors affecting kinetics of desulfurization, such as the transitory reaction parameter E, rate constant for permanent contact reaction K, can be determined by means of experimental and industrial practice results, respectively. The influence of E and K on sulfur content in hot metal is discussed. The model will be available for predicting the variation of sulfur content in hot metal and will contribute to control automatically for the desulfurization process.
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  • Effect of Slag Foaming on the Reduction of Iron Oxide in Molten Slag by Graphite

    pp. 1084-1090

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    DOI:10.2355/isijinternational.32.1084

    A kinetic study has been made on the reduction of iron oxide in molten slag, held in an alumina crucible under argon gas atmosphere, with graphite, cylindrical in shape. The composition of the primary slag was 20.5%Li2O-38.4%CaO-41.1%SiO2 (molar ratio=1:1:1). The initial concentration of iron oxide was changed between 3% and 12.5%. The experimental temperature was 1300°C. The rotation speed of the graphite cylinder was varied from zero to 1900 rpm. The reaction rate was largely affected by slag foaming. At higher FeO concentrations, the apparent rate constant was almost independent of the mechanical stirring. At lower concentrations, the effect of the rotation on the apparent rate constant was found to be small at lower speeds but tended to become larger at higher speeds. This was an indication that the melt was strongly agitated by CO gas bubble evolution. The effect of foaming is taken into account by introducing gas holdup factor into ordinary (foam-free) kinetic equations. Values of the mass transfer coefficient of oxygen in the molten slag, calculated by applying the penetration theory, are close to those of the apparent rate constant, measured experimentally. This implies that the rate of the reduction is controlled predominantly by the mass transfer in the slag phase.
  • Deoxidation Equilibrium of Silicon in Liquid Nickel and Nickel-Iron Alloys

    pp. 1091-1096

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    DOI:10.2355/isijinternational.32.1091

    The deoxidation of liquid nickel with silicon has been determined at temperatures between 1500 and 1650°C using quartz crucibles in order to investigate the deoxidation of nickel based alloys. The effect of temperature on the equilibrium constant of the deoxidation reaction:SiO2(s)=Si+2Owas found to be:log KSi(Ni)= – 15680 / T + 1.83 while the deoxidation product, log K'Si(Ni) ( = [%Si][%O]2), up to 2 mass% of silicon was expressed as follows:log K'Si(Ni)=log KSi(Ni) – 0.06[%Si]The deoxidation of nickel–iron binary with 0.5 mass% silicon has been measured over all the ranges of the binary system including pure iron at temperature of 1600 and 1650°C. On the nickel basis, the deoxidation product of nickel–iron alloys, which increased by the addition of iron up to 20 mass%, was empirically represented to be:log K'Si(Ni–Fe) = log KSi(Ni)–(288 / T–0.197)[%Fe]The temperature dependence of the equilibrium constants for the deoxidation of iron was given by the expression:log KSi(Fe) = – 30960/T+11.86at temperatures between 1550 and 1650°C. On the iron basis, the value of log K'Si(Fe–Ni)' which decreased with the increase of nickel content up to 60 mass%, was calculated as:log K'Si(Fe–Ni) = log KSi(Fe) – 0.01[%Ni].
  • Deoxidation Equilibrium of Silicon in Liquid Nickel-Chromium, Nickel-Molybdenum and Nickel-Tungsten Alloys

    pp. 1097-1101

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    DOI:10.2355/isijinternational.32.1097

    In order to understand the effect of various alloying elements on the equilibrium constant of the doeixidation of liquid nickel, the doexidation of nickel based alloys with silicon has been measured at tempertures between 1550 and 1650°C by the use of quartz crucibles.
    In nickel-chromium alloys containing 0.65 mass% silicon, the deoxidation product, log K'Si(Ni-Cr) (=[%Si][%O]2), which drastically increased by the addition of chromium until 20 mass%, was empirically represented to be:log K'Si(Ni-Cr) = log KSi(Ni) + 0.347[%Cr] – [%Cr]2below 15 mass% chromium, while the deoxidation product in nickel-molybdenum alloys containing 0.65 mass% silicon, log K'Si(Ni-Me), which also linearly increased with the increase of molybdenum content up to 16 mass%, was given the expression:log K'Si(Ni-Mo) = log KSi(Ni) + 0.047[%Mo]In nickel-tungsten alloys bearing 0.4 mass% silicon, the value of the deoxidation product was found to be as follows:log K'Si(Ni-W) = log KSi(Ni) + 0.007[%W]up to 11 mass% tungsten.
    For the effect of the alloying elements on the activity coefficient of oxygen in nickel, the following parameters wre obtained:log fO(Ni)Cr= – 0.171[%Cr]     Cr<5 mass%
    log fO(Ni)Mo= – 0.025[%Mo]    Mo<16 mass%
    log fO(Ni)W = – 0.004[%W]     W<11 mass%
  • Hot Ductility of High Purity Steels Containing Niobium

    pp. 1102-1109

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    DOI:10.2355/isijinternational.32.1102

    Ductility of high purity steels containing niobium was investigated at low strain rates at temperatures ranging from higher ferrite-pearlite region to lower austenite region. Ductility loss is observed at temperature where austenite phase is stable regardless of loading, and it increases with decreasing temperature. Ductility shows minimum at temperature where ferrite phase is induced to form by loading. Hot ductility reduces with increase of niobium content. At the temperature corresponding to minimum ductility, crack and thin film of ferrite are formed along grain boundary, but their location does not always coincide with each other. Grain boundary is easy to move at higher temperature with good ductility, whereas grain boundary keeps straight during deformation at temperature range with poor ductility. Very fine niobium carbide particles are homogeneously precipitated by deformation at austenite temperatures, and then no precipitate free zone can be found. Aluminum deepens and widens the ductility trough by coprecipitating with niobium during deformation, manganese shifts the ductility loss to lower temperature, and nitrogen slightly deteriorates hot ductility. The cause of the ductility loss is proposed on the basis of the role vacancies. Both dynamic recovery and grain boundary migration are depressed by the fine particles, and some amount of dislocation pile up occurs at grain boundaries, to which vacancies diffuse to annihilate the dislocation, and the incompatibility of the strain. Microvoids are nucleated as far as the grain boundary is immobile due to locking by either segregation of impurities or fine precipitation, and microvoids coalesce to form crack along grain boundary. The ferrite formation relaxes the grain boundary incompatibility and recovers the ductility.
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  • Effect of Retained Austenite on Formability of High Strength Sheet Steels

    pp. 1110-1116

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    DOI:10.2355/isijinternational.32.1110

    Effects of retained austenite on press formability were investigated, using austempered 0.4C-Si-1.2Mn sheet steels with high tensile strength of more than 980 MPa.
    The results showed plausible relationships between formability and initial volume fraction of retained austenite (Vγ0). With an increase in Vγ0, height of stretch forming increased linearly to its maximum at about 0.2Vγ0, and bending as well as expanding of a mechanically ground hole were gradually improved to the best at 0.15 to 0.2Vγ0. On the other hand, expanding of a punched hole was slightly deteriorated with increasing Vγ0 in less than 0.15-0.2Vγ0. These various types of formability were all extraordinarily deteriorated beyond 0.2Vγ0 in stretch forming and 0.15-0.2Vγ0 in the others.
    It was concluded that these effects of retained austenite on formability can be clearly understood in terms of Vγ0 and k: a rate constant relating rate of deformation-induced transformation with uniaxial tensile strain, as a parameter showing stability of retained austenite in press forming.
  • An Analysis of the Cr-Fe-Mo-C System and Modification of Thermodynamic Parameters

    pp. 1117-1127

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    DOI:10.2355/isijinternational.32.1117

    The thermodynamic properties of the Cr-Mo-C and Cr-Fe-Mo-C systems are analysed, and the parameters in the thermodynamic models of the two systems are revised in order to introduce a recent modification of the description of the Cr-C system. More experimental information on the Cr-Fe-Mo-C system is taken into account in the present assessment, which was ignored in previous ones. Particular attention is paid to the thermodynamic properties at temperatures below 1273 K. A new set of parameter values describing the Gibbs energy of various phases is obtained. A number of calculated sections of the Cr-Mo-C and the Cr-Fe-Mo-C phase diagrams are presented and compared with experimental information. The present calculation shows better agreement with experimental results than the previous assessments.
  • A New Method of Deriving Fundamental Rate Equations for Ostwald Ripening

    pp. 1128-1129

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    DOI:10.2355/isijinternational.32.1128

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