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

ISIJ International Vol. 33 (1993), No. 3

  • Measurements of Silicon Activities in Fe-C-Si and Fe-B-Si Alloys Using Electrochemical Silicon Sensors

    pp. 347-351

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    DOI:10.2355/isijinternational.33.347

    A simple electrochemical silicon sensor was fabricated using a solid MgO-stabilized ZrO2 electrolyte oxygen sensor with ZrO2+ZrSiO4 auxilliary electrode. Silicon activities in liquid Fe-C-Si and Fe-B-Si alloys were measured using the sensor at 1 773 and 1 715 K, respectively. Reliable measurements were preformed in Fe-C-Si melts at up to 3 wt% Si and in Fe-B-Si melts at up to 10 wt% Si. Results were in good agreement with calculated values from melt compositions. The value of 0.23 was proposed for the interaction coefficient, eSiB, at 1 715 K. The silicon sensor was proved to be applicable for the in situ determination of silicon activities or concentrations in Fe-C-Si and Fe-B-Si melts.
  • Manganese Distribution between a Slag and a Bath of Molten Sponge Iron and Scrap

    pp. 352-360

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    DOI:10.2355/isijinternational.33.352

    Sponge iron and scrap were charged and melted in a 70 ton UHP electric arc furnace. Samples of molten metal and slag were taken and the data obtained from their analysis were used to investigate the effects of some process parameters on the thermodynamics and kinetics of manganese oxidation.
    The present work shows that the activity coefficient of (MnO) is mainly dependent on temperature and varies only slightly with the basicity. The partial molar enthalphy of solution of MnO in the slag is 45.3 kJ/mol. The activity of (MnO) varies linearly with the concentration in the temperature range from 1 550 to 1 670°C and basicity range between 0.63 and 3.82.
    A linear relationship between the activity of [Mn] and the concentration upto about 1 wt% has been obtained, which shows that the average value of the activity coefficient is 0.9503.
    The manganate capacity and manganese distribution ratio are influenced mainly by the temperature and slightly by the basicity.
    The rate controlling step in manganese oxidation is the transport of manganese to the slag-metal interface. The activation energy of manganese oxidation is 63.4 kJ/mol. The mass transfer coefficient and the diffusion coefficient of manganese are 0.0226 cm/s and 7.0×10–5 cm2/s respectively at 1600°C.
  • Effects of the Viscosity of Liquid on the Characteristics of Vertical Bubbling Jet in a Cylindrical Vessel

    pp. 361-368

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    DOI:10.2355/isijinternational.33.361

    Water and aqueous glycerol solutions were used to examine the effects of the viscosity of liquids on the bubble dispersion in vertical bubbling jets. Gas holdup, bubble diameter, and bubble rising velocity were measured using the electro-resistivity probe method. Observation of bubbles was made by means of Schlieren method and a high speed video camera system. With increasing the viscosity, bubbles tended to flock together around the center line of the vessel and rise after the foregoing bubble. The radial distributions of gas holdup were classified into four types as functions of the axial distance, gas flow rate and the viscosity of liquid. Correlations of gas holdup developed for air-water bubbling jets were valid for bubbling jets in aqueous glycerol solutions when the bubble Reynolds number was greater than about 400.
  • A Numerical Study on the Combustion Phenomena Occurring at the Post Combustion Stage in Bath-type Smelting Reduction Furnace

    pp. 369-375

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    DOI:10.2355/isijinternational.33.369

    The turbulent combustion phenomena in the gas phase occurring at the post combustion stage in a bath-type smelting reduction process was simulated by use of a mathematical model, which combines the simple chemical reaction system (SCRS) combustion model with instantaneous reaction up to the chemical equilibrium state allowing the concentration fluctuation and the k-ε turbulence model. The finite difference method based on the control volume approach was used to solve the transport equations which compose the mathematical model. A 100 ton capacity converter was used as the model of the bath-type smelting reduction furnace. The effects of the injecting method on the oxidation were studied mainly. The combustion reaction in the gas phase is concentrated in the vicinity of the oxygen jet boundary. The combustion flame is spread more widely with the decrease of the inlet velocity of injecting oxygen. The efficiency of the post combustion operation was evaluated by the post combustion ratio (PCR) at the outlet of furnace. The post combustion ratio increases with the decrease of inlet velocity of the injecting oxygen and with the increase of the lance height from the iron bath surface.
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  • Raw Material Feeding and Its Influence on Operation Performance of Smelting Reduction Process with a Large Amount of Slag

    pp. 376-384

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    DOI:10.2355/isijinternational.33.376

    In order to know the necessary conditions of pretreatment of raw materials and feeding technologies, fine ore and highly volatile coal were supplied to the smelting reduction furnace directly, and the relation between feeding conditions and operation performance was investigated.
    Fine materials were supplied by injection into the metal bath or by pouring with a small amount of carrier gas from above the slag layer. In injection, excessive stirring of bath causes the decrease of post combustion and the increase of iron dust generation. For fine ore, it is possible to supply by pouring with negligible carry-over, by keeping the specific surface area of a stream small.
    When coal is supplied directly, volatile matter influences the post combustion, coal consumption and the amount of carry-over of carbon. It is possible to operate a smelting reduction furnace with direct addition of coal by suppressing carry-over, but pretreatment for decreasing coal consumption further was discussed.
  • Simulation Analysis of Coal Packed Bed Type Smelting Reduction Process

    pp. 385-390

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    DOI:10.2355/isijinternational.33.385

    The simulation analysis of material and heat flow in coal packed bed type smelting reduction process, such as COREX process, was conducted by use of the computer model developed based on the heat and material balance. The simulation was conducted by focusing on the amount of volatile material in coal used in the process and the operation condition of the fluidized bed melter gasifier where the reducing gas used in the reduction shaft is generated. The coal consumption decreases with decrease amount of the volatile material in coal. By increasing the oxidation degree of off-gas from the fluidized bed melter gasifier, the coal consumption decreases but the increasing amount is limited by the requirements of reduction shaft. The simulation results show that it is important for efficient process to control the volume and temperature of off-gas from the fluidized melter gasifier to be matched with the requirement of reduction shaft, which is necessary for reducing the amount of gas scrubbed and cooled as much as possible. It can be accomplished by using the low volatile coal and by increasing the oxidation degree of off-gas from the fluidized melter gasifier within the allowable range.
  • Decarburization Reaction in Ultra-low Carbon Iron Melt under Reduced Pressure

    pp. 391-399

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    DOI:10.2355/isijinternational.33.391

    The kinetics of the decarburization reaction with dissolved oxygen in a liquid iron in the ultraolow carbon concentration range under reduced pressure have been studied, using an induction furnace with a 20 kg melt. The results obtained are as follows:
    (1) The decarburization reaction proceeds to less than 5 ppm of carbon, and the decarburization rate constant, K, decreases as the carbon content decreases.
    (2) As the pressure in the chamber decreases, the decarburization rate increases with a carbon content of more than 10 ppm. On the other hand, the dependency of decarburization rate on the pressure in the chamber is small, with less than 10 ppm of carbon.
    (3) The influence of the sulphur content on the decarburization rate is small with a carbon content of more than 10 ppm. The decarburization rates are not affected by the mass transfer of CO in the gas phase under experimental conditions. Thus, it is concluded that the decarburization rate is controlled by the mass transfer of carbon in liquid iron.
    (4) The fact that the decarburization rate at a carbon content of more than 10 ppm is affected by the total pressure of the chamber has been explained by the change in interfacial area of the reaction between the gas and liquid phases resulting from CO boiling in the bulk melt.
    (5) The decrease in the decarburization rate in t he ultra-low carbon concentration range in RH is also caused by the decrease in interfacial area of the reaction between the gas and liquid phases.
  • Fabrication of Small Aluminum Ingot by Electromagnetic Casting

    pp. 400-404

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    DOI:10.2355/isijinternational.33.400

    In this study, as the first step to explicate the fundamental phenomena of Electromagnetic Casting (EMC), we provided an electromagnetic force generated by an electric source of 20 kW, 3 kHz and a electromagnetic coil with 18 turns to the molten aluminum. After confirming a stable meniscus in the electromagnetic mold, the bottom block was drawn in vertical direction. And a cylindrical aluminum ingot which size can be varied from 30 to 60 mm in diameter was fabricated. This ingot has the luster and the smooth surface typical for EM cast. Microstructural observation showed that the secondary dendrite arm spacing was 6 to 8 μm.
  • Apparent Viscosity of Al-10mass%Cu Semi-solid Alloys

    pp. 405-412

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    DOI:10.2355/isijinternational.33.405

    Cold model and stirring experiments for Al-10mass%Cu semi-solid alloys by continuous cooling investigated factors affecting viscosity and the relationship between apparent viscosities and stirring conditions of semi-solid alloys.
    In the cold model experiments, the suspension viscosity of spherical particles was lower than that of irregularly shaped particles, and decreased with the broadening of particle size. These behaviors were explained very well by the equation proposed by Mori-Ototake that defines viscosity as a function of particle shape, the critical fraction of solid for fluidity and the fraction of solid of suspension. The coefficients of this equation were determined by fitting the measured apparent viscosities of Al-10mass%Cu semi-solid alloys using regression method. The measured values were well fitted to the determined curves of this equation. And it has been shown that the determined coefficients varied with solidification rate and shear rate. The apparent viscosity increased with increasing solidification rate and increasing shear rate. The critical fraction of solid for fluidity increased with decreasing solidification rate and increasing shear rate. These results depended on the shapes of suspended particles in semi-solid alloys. In dendritic structures with many arms or network structures, the viscosity was increased and the critical fraction of solid was decreased. The apparent viscosity equation of Al-10mass%Cu semi-solid alloy proposed was:
    ηaLa{1+(2.41×105C1/3γ−4/3)/[2(1/fs−1/(0.72−8.82C1/3γ−1/3))]}    (Pa · s)
  • Influence of Heat Treatment and Carbon Content on the Hot Ductility of Nb-Ti Microalloyed Steels

    pp. 413-419

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    DOI:10.2355/isijinternational.33.413

    The influence of C and heat treatment on the hot ductility of Nb-Ti microalloyed steels, in the temperature range 800 to 1300°C, was investigated by tensile testing at low strain rates. The C range was varied between 0.07 and 0.14 wt% (peritectic composition). The heat treatments involved direct heating to the test temperature, annealing at 1330°C and subsolidus reheating at 1480°C . The increase of the C content to 0.14 wt% slightly affects the hot ductility after the direct heating and annealing treatments. However, after subsolidus reheating, the width of the ductility trough is increased in the 0.14 wt% C steel. This effect is attributed to the coarser austenite structure inherited from this prior heat treatment.
  • Nitriding of Fe-Cr Powdered Alloys by Ball Milling in Nitrogen Gas

    pp. 420-425

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    DOI:10.2355/isijinternational.33.420

    Elemental iron and Fe100-XCrX (X=30, 50 and 70) powder mixtures were milled in a vibrational ball mill under nitrogen atmosphere. Structural changes during milling, and thermal stabilities and magnetic properties of the milled powders were examined by means of X-ray analysis, HRTEM, DSC and Mössbauer spectroscopy. It was found that Fe-Cr-N powdered alloys with very high concentrations of nitrogen were able to be prepared by this technique. The structure of the powder particles was composed of nanometer-sized b.c.c grains supersaturated with nitrogen. With the nitrided Fe50Cr50 alloy, the grain size decreased to about 2 nm after alloying with about 12 ar% of nitrogen, and then X-ray diffraction took on an amorphous-like pattern. On annealing of the nitrided powders, a heat evolution due to the precipitation of chromium nitride was observed at temperatures around 850 K. The Mössbauer analysis revealed that the nitrided Fe70Cr30 alloy had paramagnetic and ferromagnetic components. The nitrided Fe50Cr50 alloy became entirely paramagnetic after the reduction in grain size below about 5 nm.

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