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

ISIJ International Vol. 31 (1991), No. 9

  • Mechanisms of Hanging Caused by Dust in a Shaft Furnace

    pp. 939-946

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    DOI:10.2355/isijinternational.31.939

    The mechanism of hanging caused by the dust in reducing gas in the reduction shift furnace was investigated. Through experimental studies using a rectangular model and theoretical studies using a two dimensional mathematical simulation model, it was clarified that the dust in reducing gas stuck on the packed particles to form a dust blockade zone in front of tuyeres and when the dust concentration of reducing gas was increased or the descending velocity of packed bed was decreased, the dust blockade zone expanded and the gas pressure drop increased to cause hanging.
  • Buoyancy and Expansion Power in Gas-agitated Baths

    pp. 947-951

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    DOI:10.2355/isijinternational.31.947

    The derivation of the energy input to a gas-stirred bath is re-examined. The formula for the work done by the expansion of gas due to pressure decrease as it rises through the bath is found to be different from that given in the literature. According to the previous derivation, this energy input is numerically equal to the work done by the buoyancy force, but the present formula gives a much lower value. The so-called 'buoyancy power', which is conventionally taken to be the sum of this expansion power and the power due to the buoyancy force itself, is therefore approximately half the value given by the previously published formulas. A similar correction applies to the work done by the gas as it expands due to heating in a pyrometallurgical bath: the new formula is smaller than the published one by a factor equal to the ratio of the static pressure drop across the bath to static pressure at the bottom of the bath.
  • Bubble Characteristics in the Momentum Region of Air-Water Vertical Bubbling Jet

    pp. 952-959

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    DOI:10.2355/isijinternational.31.952

    The flow field in vertical bubbling jet in a cylindrical vessel was found to be divided into four regions. They were named the momentum, transition, buoyancy and surface regions from the nozzle exit toward the bath surface. However, the bubble characteristics in each region have not been made clear even in air-water bubbling jets. The present paper proposed empirical correlations for bubble frequency and gas holdup in the momentum region of air-water vertical bubbling jet. The momentum region was defined as the region where the gas holdup on the centerline decreased from 100 to about 10%. These correlations were applicable to bubbling jets of the modified Froude number from about unity to 2×105.
  • Effect of Varying Ladle Stream Temperature on the Melt Flow and Heat Transfer in Continuous Casting Tundishes

    pp. 960-967

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    DOI:10.2355/isijinternational.31.960

    The effect of varying ladle stream temperature on the fluid flow and heat transfer phenomena in a typical twin strand slab caster tundish has been mathematically modeled in the present study. The model involves solution of the transient, three dimensional form of the turbulent Navier-Stokes' equation, along with the equations of turbulence energy, energy dissipation rate of turbulence energy and thermal energy conservation. The incoming melt stream temperature has been assumed to decline at a constant rate of 0.5°C/min over a casting period of 50 min. Under the conditions examined in the present mathematical model, the temperature of the incoming melt stream becomes lower than the bulk temperature of the melt in the tundish by about 1-2°C, after 25 min from the start of teeming of a heat. Due to buoyancy effects, the cooler incoming melt starts to flow along the bottom of the tundish instead of the normal top free surface directed flow. The calculations show that the inverse flow pattern develops over the remainder of the teeming period and persists for about 1 min into the teeming of the next heat. Thus, the inclusion flotation and removal of the non-metallic inclusions during the later half of the casting period are expected to be worse compared to the first half.
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  • Electromagnetic Atomization of Molten Metals

    pp. 968-972

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    DOI:10.2355/isijinternational.31.968

    A new atomization process for molten metal is proposed. The electromagnetic energy induced by direct electric current and stationary magnetic field is utilized in the process instead of kinetic energy as in the fluid impingement and disk rotation which have been used in the conventional metal atomization processes. In order to improve the controllability of this process, splashing phenomena were carefully examined and main obstacles interrupting the continuous operation of the process and obtainment of the sharp particle distribution were searched and removed. A mathematical model was proposed for better understanding of the process. On the basis of the visualization of splashing phenomena and the calculated results of the mathematical model, it was found that the particle size can be mainly controlled by the distance between the nozzle and the electrode, the delay time of the electric current and the mass flow rate of molten metal. The impulse defined as the product of the electric current and the duration of the electric current, and the momentum defined as the product of the mass and the velocity of a splashed particle were calculated from the observed data. From the linear relation found between the impulse and the momentum, the efficiency in which electromagnetic energy was transformed into the kinetic energy for splashing a particle was evaluated.
  • Analysis of Warping Phenomenon in Plate Rolling

    pp. 973-978

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    DOI:10.2355/isijinternational.31.973

    Warping in plate rolling causes the decrease in productivity, the deterioration in product quality, and at times damage of the equipment. Because warping is generally caused by multiple factors, it is difficult to quantify the effect of each factor on warping.
    A non-steady state deformation model based on the rigid-plastic FEM was therefore developed to analyze warping phenomenon and is capable of dealing with the deformation of material during asymmetrical rolling. Analysis with this model was carried out at varying speeds of upper and lower roll speeds, coefficients of friction, and material temperatures.
    Also a simulation model was developed by combining the non-steady state deformation model with a torsional vibration model of the driving system of a mill.
    As the results of analysis by these models, the effect of asymmetrical conditions on warping depends on the shape factor ld/hm (length of contact/mean thickness).
    Experiments were made in a commercial mill to verify these simulation models, confirmed that the analysis of warping phenomenon by means of these model is possible.
  • Determining Transient Temperature Distribution in Solids from Measurements of the Surface Temperature

    pp. 979-984

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    DOI:10.2355/isijinternational.31.979

    The paper is concerned with a method that enables one to determine transient temperature distribution in a heat conducting body from measurements of the surface temperature. It means that an initial condition is not necessary. The solution can be obtained using analytical or numerical methods. It is presented in terms of a series containing the derivatives of the surface temperature with respect to time. In order to calculate the derivatives the regularization method is employed. Some test cases are included. They prove that the proposed method can produce stable results for a wide range of problems except for rapid processes of heat conduction. It means that the method can be employed when, e.g. one estimates the temperature distribution within blooms or ingots during heating or cooling under moderate conditions.
  • Production and Properties of Carbide Dispersion-strengthened Coppers by Compocasting

    pp. 985-991

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    DOI:10.2355/isijinternational.31.985

    An investigation was made on the electrical and mechanical properties of dispersion-strengthened (DS) coppers compocast at 25 rev/sec with the addition of fine carbide particles in the range of 0.5 to 30 mass% WC, TaC, VC, TiC, NbC, ZrC, Mo2C, Cr3C2 and Al4C3. Homogeneous dispersion of carbides was observed in the microstructures of the compocast DS coppers except with the addition of Mo2C, Cr3C2 or Al4C3. The measured values of electrical conductivity of the DS coppers were 77.9%IACS at 20 mass% WC, 73.4%IACS at 20 mass% TaC, 72.0%IACS at 10 mass% NbC, 85.2%IACS at 5 mass% TiC and 68.9%IACS at 5 mass% VC. The values of Vickers hardness were HV 197 at 30 mass% WC, HV 155 at 30 mass% NbC, HV 110 at 30 mass% TaC, HV 158 at 20 mass% VC and HV 121 at 20 mass% TiC. Ultimate tensile strength values were 402 Mpa at 30 mass% NbC, 357 Mpa at 20 mass% TiC, 330 Mpa at 20 mass% WC, 269 Mpa at 20 mass% TaC and 323 Mpa at 10 mass% VC. The values of elongation were 12.9% at 20 mass% TaC, 10.9% at 20 mass% WC, 25.2% at 10 mass% NbC, 21.8% at 10 mass% VC and 17.5% at 5 mass% TiC.
  • Effects of Silicon and Manganese Addition on Mechanical Properties of High-strength Hot-rolled Sheet Steel Containing Retained Austenite

    pp. 992-1000

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    DOI:10.2355/isijinternational.31.992

    An 80 kgf/mm2 grade high-strength hot rolled sheet steel with a significantly high product of tensile strength and total elongation (TS×EI=3 000) has been developed by utilizing transformation-induced plasticity of retained austenite in 0.2% carbon sheet steels by optimizing the silicon and manganese content and hot rolling conditions. Finish rolling temperature and coiling temperature are important factors in terms of introducing a large amount of retained austenite. Silicon addition over 1.0% results in a significant increase in the volume fraction of retained austenite due to the change in second phase from bainite+pearlite to bainitic ferrite. The maximum volume fraction of retained austenite and the consequential optimum combination of tensile strength and ductility is obtained in a 0.2%C-2.0%Si-1.5%Mn steel. The effect of retained austenite on ductility becomes small with further addition of manganese over 1.5%, because the retained austenite transforms in the early stage of the straining process due to the presence of martensite.
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  • Creep-fatigue of 1Cr-Mo-V Steels under Simulated Cyclic Thermal Stresses

    pp. 1001-1006

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    DOI:10.2355/isijinternational.31.1001

    Isothermal long term creep-fatigue tests and combined temperature-strain cycling tests were conducted with the newly developed testing machines suitable for long term running. The aim of these tests was to establish a more reliable method for the life prediction of structural components subjected to complex stress-strain histories due to load-temperature variations. Three heats of 1Cr-Mo-V forged steels widely adapted for steam turbine rotors were sampled and the differences of creep-fatigue properties due to technological evolution of steel making were examined. The two heats were produced in the 1960s and the one in the 1980s. The results were analyzed by the life prediction method proposed by the present authors, which was characterized by a quantitative description of the materials degradation with time based on the creep rupture ductility.
  • Effect of Silicon Content on Secondary Recrystallization in Grain-oriented Electrical Steel Produced by Single-stage Cold Rolling Process

    pp. 1007-1012

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    DOI:10.2355/isijinternational.31.1007

    A study was made on the effect of the silicon content on secondary recrystallization in grain-oriented electrical steel produced by the single-stage cold rolling process where both MnS and AlN are utilized as inhibitors. The following conclusions were derived from the study:
    (1) The onset and progress of secondary recrystallization are retarted when the silicon content is increased from 3.0 to 3.3 mass% No secondary recrystallization occurs when the silicon content is increased further to 3.7 mass%.
    (2) This secondary recrystallization behavior may be ascribed to the decrease in the {110} density of primary-recrystallized texture, the increase in the mean diameter of primary-recrystallized grains, and the decrease in the inhibiting effect with the increase in the silicon content.
  • Effect of Cold Rolling Reduction on Secondary Recrystallization in Grain-oriented Electrical Steel Produced by Single-stage Rolling Process

    pp. 1013-1019

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    DOI:10.2355/isijinternational.31.1013

    A study was made on the effect of cold rolling reductions of 80 to 94% on secondary recrystallization in grain-oriented electrical steel produced by the single-stage cold rolling process. The following conclusions were derived from the study.
    (1) As the cold rolling reduction increases, secondary-recrystallized grains increase in diameter, and fine grains other than Goss oriented grains start to develop and eventually fill the entire sheet section. This may be ascribed to the decrease in the amount of Goss nuclei in the primary-recrystallized matrix as a result of the increased cold rolling reduction.
    (2) As the cold rolling reduction increases, secondary-recrystallized grains, other than fine grains, increase in sharpness to the ideal Goss orientation. This may be ascribed to the increase in the amount of orientations in the Σ9 coincidence relationship with the ideal Goss orientation.
    (3) Secondary recrystallization is affected more greatly by the change in the texture than by the change in the diameter of primary-recrystallized grains as a result of the increased cold rolling reduction.
  • Characterization of Precipitates in Vanadium and Titanium Microalloyed Steels

    pp. 1020-1025

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    DOI:10.2355/isijinternational.31.1020

    Transmission electron microscopic observations were carried out on carbon extraction replicas prepared from two commercial V-microalloyed steels and one commercial Ti-microalloyed steel hot rolled to 10 mm diameter bars at different rolling conditions.
    The presence of about 0.13% Cu in V- or Ti-microalloyed steels led to the formation of copper sulphides preferentially rather than manganese sulphides although the steels containing more than 1% Mn. In Ti-microalloyed steel, globular titanium carbosulphides of the type Ti4C2S2 are observed in addition to copper sulphide.
    In V-steels, transmission electron microscopy revealed very fine precipitates in the pro-eutectoid ferrite (≅5 nm) which are identified as carbides or carbonitrides of the type M (C, N) (M=V and Cr, where V/Cr≅5). Some relatively coarse particles (≅0.1 μm) were also observed (with V/Cr>15) which are suggested to be V-nitrides or carbonitrides formed at relatively high temperatures in austenite.
    In Ti-steel, coarse titanium nitride particles (>5μm) were observed together with precipitates of the type MC (M=Ti and Cr) in the form of very fine precipitates (≅5 nm, Ti/Cr≅9) or relatively coarse carbide particles (≅0.1μm, Ti/Cr>30).

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  1. blast furnace
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