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

ISIJ International Vol. 31 (1991), No. 1

  • State of the Art in Precoated Steel Sheet for Automotive Body Materials in Japan

    pp. 1-10

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    DOI:10.2355/isijinternational.31.1

    The history of precoated steel usage as car body materials in Japan is reviewed first. Japanese steelmakers developed galvannealed steel, duplex Zn–Fe coated steel, Zn–Ni coated steel and organic composite coated steel. All of them have been widely used. Recently, electrolytically Fe–Zn plated galvannealed steel and 1μm thick organic painted Zn–Ni electroplated steel have been applied. They have not only excellent corrosion resistance, but also good paintability, formability and weldability. Car body corrosion is classified into cosmetic corrosion and perforation. Newly clarified mechanisms for these two are explained. As for current research subjects, the development of inorganic and organic dispersion coating, Zn–Mn plating, galvannealed steel by vapor deposition, and vapor phase deposited Zn–Mg coating are described. Surface roughness control, application to vibration damping sheet, adhesive bonding, and the adaptation to lightweight cars are also important subjects to be studied now.
  • Reduction of Microwave Irradiated Iron Ore Particles in CO

    pp. 11-16

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    DOI:10.2355/isijinternational.31.11

    The effect of microwave (2.45 GHz) pre-treatment on the reduction of magneto-hematite ore particles in CO was investigated. It was found that the presence of magnetite in the ore has considerable effect on the microwave treatment and that the oxidation of the goethite, present in the ore, is obtained after the magneto-hematite grains are almost entirely oxidized to hematite.
    The results of the reduction tests show that microwave treatment enhances reduction but benefit optima exist. In the present ore optimum reduction was obtained for an irradiation of 6 min at a power level of 1 300 W. It is also shown that in addition to a reducibility gain post-reduction strength and decrepitation were likewise improved by microwave treatment.
  • Factors Governing the Strength of Agglomerated Granules after Sintering

    pp. 17-23

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    DOI:10.2355/isijinternational.31.17

    Segregations of materials exist more or less in iron ore sintering beds and they are essential for the sintering process. Therefore, control of the segregations can be a key technology to improve the performance of the process. Granule design for raw materials seems to be an effective technology to realize it. However, there is still insufficient information available for establishing the technology. This study focused to estimate factors governing the strength of sintered granules and following results were obtained: Fluidity of the fine mixtures in high temperatures can be qualitatively estimated considering liquidus temperature indicated in an appropriate phase diagram which corresponds to the main components of the mixtures. Fair linear relations were obtained between the fluidity of the adhering layers of each type of model granules and the strength of the sintered granules. Chemical composition of the adhering layers and fraction of large (+0.01 mm) pores and loss on ignition of the core particles are the estimated dominant factors governing the strength of sintered granules.
    x

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    1. Commercial Production of Iron Ore Agglomerates Using Sinter Feeds Containing a Large Amount of Fine Ores ISIJ International Vol.33(1993), No.4
    2. Mechanisms of Hanging Caused by Dust in a Shaft Furnace ISIJ International Vol.31(1991), No.9
    3. Prediction of a Blast Furnace Burden Distribution Variable ISIJ International Vol.36(1996), No.9
  • Heat Transfer Simulation on Drying Processes of Nonfired Pellets Containing Combined Water in the Moving Bed Reactor

    pp. 24-31

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    DOI:10.2355/isijinternational.31.24

    Attention has been focussed on nonfired pellets used in ironmaking industries from the point of view of energy saving. Heat transfer experiments for nonfired pellets were carried out for the better understanding of the fundamental process characteristics which would provide the basis for utilization technology of nonfired pellets. Heat transfer characteristics were investigated by both numerical simulation and experiments using moving beds. Decomposition rate of combined water contained in the nonfired pellets and temperature dependence of effective thermal conductivity were measured by means of TG-DTA and laser flash method, respectively. Heat transfer coefficient between gas and solid in the moving bed was determined by using fired pellets and a correlated equation was proposed. One dimensional mathematical model developed here provided excellent agreement between estimated temperature distribution in the moving beds and observed data.
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    Readers Who Read This Article Also Read

    1. Mechanisms of Hanging Caused by Dust in a Shaft Furnace ISIJ International Vol.31(1991), No.9
    2. Prediction of a Blast Furnace Burden Distribution Variable ISIJ International Vol.36(1996), No.9
    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
  • Disintegration of Coke by Mechanical Impact under Gasification Reaction

    pp. 32-39

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    DOI:10.2355/isijinternational.31.32

    In order to elucidate the behavior of coke fines in blast furnace, fundamental experiments were carried out on the disintegration of coke during gasification reaction accompanied by mechanical impact.
    The following results were obtained:
    (1) Coke fines of high ash content are generated with the progress of gasification, which suggests the close correlation between generation of coke fines and gasification.
    (2) Coke fines generate increasingly when the mechanical impact strength is beyond a critical value.
    (3) Reaction temperature, gas composition and coke size also affect the generation of coke fines causing a different rate of gasification.
    A mathematical model was introduced using the rate equation of coke fine generation based on the experimental results. The calculation results by this model agree very well with the experimental results. The model, therefore, is supposed to be applied for the investigation of the behavior of coke fines in blast furnaces.
    x

    Readers Who Read This Article Also Read

    1. Mechanisms of Hanging Caused by Dust in a Shaft Furnace ISIJ International Vol.31(1991), No.9
    2. Prediction of a Blast Furnace Burden Distribution Variable ISIJ International Vol.36(1996), No.9
    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
  • Numerical Analysis of Fluid Flow in Continuous Casting Mold by Bubble Dispersion Model

    pp. 40-45

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    DOI:10.2355/isijinternational.31.40

    Surface and internal defects of cold rolled steel sheet attributable to steelmaking conditions arise from the entrapment, by the solidifying shell in the continuous casting mold, of alumina clusters, mold powder, and argon gas bubbles blown into the immersion nozzle. In order to prevent such defects, it is necessary to control the fluid flow of molten steel in the mold. In this study, actual-scale water model experiments were first carried out to investigate in detail the fluid flow patten and distribution of local gas holdup in the mold. Subsequently, a hydrodynamic analysis model was developed considering the effect of the buoyant force of gas bubbles on fluid flow and the continuity of local gas holdup (bubble dispersion model). This model has made it possible to estimate the liquid velocity profile, and the distributions of local gas holdup and inclusions in the mold.
    x

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    1. The Flow Field in Air-Water Vertical Bubbling Jets in a Cylindrical Vessel ISIJ International Vol.31(1991), No.3
    2. Computer Aided Interfacial Measurements ISIJ International Vol.32(1992), No.1
    3. Interfacial Properties of Liquid Iron Alloys and Liquid Slags Relating to Iron- and Steel-making Processes ISIJ International Vol.32(1992), No.1
  • The Melting Process of Rectangular Prisms Immersed in Bubbling Jet in a Cylindrical Vessel

    pp. 46-52

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    DOI:10.2355/isijinternational.31.46

    Very high turbulent fluctuation inherent in bubbling jet suppresses the separation of boundary layer developing on the surface of a body immersed in the jet and makes fluids in the bulk layer contact with it from all directions. Therefore, as the turbulence increases, the local heat transfer coefficient around the body is supposed to have almost the same value all over the surface and become independent of the shape of the body. This was found to be true from the facts that a rectangular ice prism melted away while keeping the similar profiles and that the local heat transfer coefficient was well approximated by the mean heat transfer coefficient of a sphere. On the basis of this result, the complete melting time of a rectangular prism was estimated by using the mean heat transfer coefficient of a sphere. The result agreed well with the experimental one. This agreement implies that the present estimation method would be applied to various non-spherical bodies immersed in bubbling jet.
  • Analytical Study of Gas-Particle Two-phase Free Jets Exhausted from a Subsonic Nozzle

    pp. 53-61

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    DOI:10.2355/isijinternational.31.53

    This paper is concerned with a numerical analysis of the flow field of gas-particle two-phase free jets exhausted from a subsonic nozzle. The flow properties of two-phase mixture in a nozzle are obtained by solving a system of equations numerically, and then two-phase flow fields in a free jet region are solved as a perturbation from the nozzle exit condition. Thus, a few numerical experiments are performed for mist flows composed of air and water-particles, which are commonly applied to the secondary cooling zone in the continuous casting. One of the most important results so obtained is that a completely steady solution, in the conventional sense, cannot be expected even in a long run. Rather, a ring vortical structure is produced near the nozzle exit somewhat periodically. This may be understood to be due to the velocity discontinuity between the two-phase jet and the ambient gas at the jet boundary. So, in this region, the gas flow fluctuates and the small particles follow the fluctuation. The fluctuation of particle motion becomes more remarkable for the smaller particles. Also, an appreciable concentration of particles occurs near the jet boundary as the particle size becomes smaller.
  • Redox Equilibria of Fe and Mn in the Na2O-B2O3 Melts

    pp. 62-68

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    DOI:10.2355/isijinternational.31.62

    The Fe2+/Fe3+ and Mn2+/Mn3+ redox equilibria in the Na2O-B2O3 melts have been individually measured as a function of the melt compositions, temperatures, oxygen partial pressures, and dopant element concentrations. The mutual interaction of these two redox couples has been studied by electron spin resonance (ESR) in the Na2O·2B2O3 melts.
    The redox ratios of Fe and Mn in the Na2O-B2O3 melts tend to decrease with increasing the dopant concentration. A plot of log [(M2+)/(M3+)] vs. -log PO2 indicated a straight line of the slope of 8 and 4 for Fe and Mn, respectively. The values for the reduction enthalpy of Fe and Mn in Na2O-B2O3 melts were found to be 80-120 kJ/mol and 40-60 kJ/mol, respectively. The redox ratio of Fe and Mn decreased with increasing the XNa2O/XB2O3 ratio. It was shown by ESR spectroscopy that the electron exchange reaction: Fe2++Mn3+=Fe3++Mn2+ proceeded to the right.
    x

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    2. Assessment of P2O5 Activity Coefficients in Molten Slags ISIJ International Vol.40(2000), No.10
  • The Effect of the Gas Jet on the Gas/Liquid Reactivity in the Metallurgical Vessel

    pp. 69-75

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    DOI:10.2355/isijinternational.31.69

    The effect of the turbulent gas jet on the reaction characteristics in gas blowing was investigated by the simultaneous measurements of gas/liquid interfacial area and gas holdup. Gas/liquid interfacial area was measured by KOH/CO2 model system on the fast pseudo first-order reaction, and gas holdup was measured by using the electrical conductivity method. By estimating the mean diameter of bubbles from the measured data of gas/liquid interfacial area and gas holdup, in the gas/liquid two phase region, the jet effect on the improvement of the reactivity was investigated.
    Both the specific interfacial area and the gas holdup were increased as the aspect ratio decreased. The variations were larger in a high gas flow rate and in a small nozzle diameter. The effect of nozzle diameter was larger in a low aspect ratio. The calculated mean diameter of bubbles was slightly increased with the increase of the nozzle diameter and the aspect ratio. The result shows that the increase in the reacting interfacial area according to the development of jet was mainly affected by the increase of gas holdup through being dense of bubble swarms in the jet.
  • Superplasticity and Newtonian-viscous Flow in Fine-grained Class I Solid Solution Alloys

    pp. 76-85

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    DOI:10.2355/isijinternational.31.76

    Elevated temperature (1 023 to 1 193 K) tensile properties are described for a fine (6 μm) and coarse (100 μm) grained ultrahigh carbon (1.25 %) steel containing 10 % aluminum. The coarse-grained steel exhibits Class I solid solution alloy behavior wherein a stress exponent of three is noted. The fine-grained steel exhibits exceptionally low stress exponents, where a stress exponent of two is observed at low strain rates and decreases to as low as 1.35 with an increase in strain rate. A creep model is developed to explain these rersults based on grain boundary sliding accommodated by two different dislocation processes. When n=2, the accommodation process is attributed to dislocation climb and when n is less than 2, dislocation solute-dragged glide becomes the important accommodation process. The model predicts ideal Newtonian-viscous flow (n=1) will occur in Class I solid solution alloys at sufficiently high temperatures and at fine-grain sizes. It is shown that the superplastic alloys Al-Mg-Cu, Ti-6Al-4V and Mg-33Al exhibit the predicted fine-grained Class I solid solution alloy behavior, whereas the superplastic alloys Ni-39Cr-10Fe-7.5Ti-1Al, Cu-39.4Zn, Fe-26Cr-6.5Ni-0.05Al, Fe-1.6C and Ag-28Cu exhibit the predicted fine-grained Class II solid solution behavior.
  • Inhomogeneous Texture Formation in High Speed Hot Rolling of Ferritic Stainless Steel

    pp. 86-94

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    DOI:10.2355/isijinternational.31.86

    Effects of inhomogeneous shear strain on the texture variation through the thickness of hot rolled ferritic stainless steel sheets are studied. The changes in texture with the progress of recrystallization are also investigated. Sheet specimens of AISI430 stainless steel are rolled at 1 000°C at a rolling speed of 20 m/s without lubrication and quenched into water at an interval of 3.5 to 250 ms after rolling. The redundant shear deformation by friction produces a severely sheared region beneath the surface, where a band of extremely fine recrystallized grains is formed when the strain exceeds a critical value.
    ‹110› || ND axis density increases and ‹111› || ND axis density decreases with increasing shear strain. The deformation texture in the severely sheared region mainly consists of {110}‹001›, {110}‹112› and {112}‹111›. At the mid-thickness, it consists of ‹111› || ND and ‹100› || ND components. Only shear deformation is required for the formation of {110}‹001› texture. The sharpness of the preferred orientation decreases by the progress of recrystallization, but some components of deformation texture are retained throughout the thickness after recrystallization is completed.
  • Prediction of Temperature Distribution, Flow Stress and Microstructure during the Multipass Hot Rolling of Steel Plate and Strip

    pp. 95-105

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    DOI:10.2355/isijinternational.31.95

    The hot rolling of steel was simulated using data from laboratory experiments and mill trials. Particular attention was paid to prediction of the temperature distribution through the thickness of the rolled plate or strip. The effects taken into account are radiation and convection from the surface when the material is between stands, and conduction to the rolls and the temperature increase due to mechanical work when the material is in the roll gap. An explicit finite difference method is used to calculate the temperature distribution through the thickness of the workpiece during processing.
    On the basis of the present temperature model and of the constitutive and recrystallization kinetics equations developed earlier for the steels under investigation, a computer model was developed for the prediction of rolling force and microstructural evolution. The predictions of these models are in good agreement with measurements on both experimental and commercial steels. They can accordingly be used for off-line applications, such as mill construction and rolling schedule design and optimization. They also constitute a step towards the on-line control of plate and hot strip mills.
    x

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  • Low Cycle Fatigue Behavior of Pressure Vessel Steels in High Temperature Pressurized Water

    pp. 106-114

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    DOI:10.2355/isijinternational.31.106

    Low cycle fatigue behavior of low alloy steels ASTM A508 C1.3(JIS SFVQ1A) and ASTM A533B C1.1(JIS SQV2A) for nuclear reactor pressure vessels was investigated in high temperature pressurized water simulating BWR coolant environments. Total strain range, strain rate and dissolved oxygen concentration were varied from 0.5 to 2.2 %, 0.1 to 0.001 %/s and 10 to 8 000 ppb, respectively. Fatigue tests in ambient air and 561 K air were also conducted for comparison.
    It was found that fatigue lives in high temperature water were shorter than those in ambient air. However, the reduction of fatigue life decreased with decreasing total strain range and rather longer fatigue lives than those in ambient air were observed at lower total strain range. A533B material showed the distinct strain rate dependence of fatigue life compared with A508 material, while they showed the similar dependence on dissolved oxygen concentration. It was found that fatigue cracks initiated at corrosion pits generated by dissolution of MnS inclusions and the low cycle fatigue behavior dependent on sulfur content of the material.
    It can be concluded that the materials tested possess safety margins in reactor coolant environments by judging from the fact that all the present data fell on a region above the design fatigue curves in the ASME Code Sec. III.

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