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

ISIJ International Vol. 29 (1989), No. 8

  • Effect of Oxygen Potential on Mineral Formation in Lime-fluxed Iron Ore Sinter

    pp. 625-634

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    DOI:10.2355/isijinternational.29.625

    In industrial iron ore sintering, the raw material is heated in a reducing atmosphere and cooled in an oxidizing atmosphere. In order to study the characteristics of mineral formation under different regimes of heating and cooling in industrial sintering, small tablet specimens made from powdered materials were sintered in a tube furnace under controlled gas atmospheres. The results obtained are summarized as follows.
    In the heating stage acicular calcium ferrite can be produced from the reaction of hematite and the flux below 1 180°C. With an increase of temperature, the calcium ferrite crystal size increases and at higher temperature the calcium ferrite transforms to magnetite and silicate melt. During the cooling stage, the magnetite tends to react with the silicate melt and oxygen to generate calcium ferrite at a medium oxygen partial pressure (around 1×10-2 atm). Reoxidized hematite is formed from magnetite at a higher oxygen potential (e.g., 5×10-2 atm). The magnetite (produced in the heating stage) is preserved at a low oxygen potential. Acicular calcium ferrite may also be generated from magnetite ore at high oxygen potential (e.g., PO2>5×10-3 atom) during the heating stage of sintering.
    Calcium ferrite produced from the reaction of hematite and the flux in heating stage is a form of calcium diferrite (CaO·2Fe2O3) with some substitution of Si and Al. The composition of calcium ferrite generated from magnetite depends on the amounts of SiO2 and CaO from silicate melt reacting with magnetite. The basicity (mole ratio of CaO/SiO2) of silicate melt consumed in the reaction is around 2.
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    1. Sintering Conditions for Simulating the Formation of Mineral Phases in Industrial Iron Ore Sinter ISIJ International Vol.29(1989), No.1
    2. Effect of Oxygen Partial Pressure on the Formation Mechanisms of Complex Ca-rich Ferrites ISIJ International Vol.53(2013), No.5
    3. Recent Progress in Iron Ore Sintering Tetsu-to-Hagané Vol.68(1982), No.15
  • An Analysis of the Structure of Iron Ore Sinter Cake

    pp. 635-641

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    DOI:10.2355/isijinternational.29.635

    Physical properties of sinter cake such as strength and permeability are strongly related to its structure. In this investigation, the 3-dimensional structure of voids in sinter cakes prepared from raw mix with a range of coke contents was quantified using image analysis. The physical properties were then compared with the measured structural parameters.
    The results obtained are of a preliminary nature and the interpretations are not conclusive. However, a possible way to evaluate sinter strength was identified which utilizes the measured values of void fraction and specific surface area of the sinter cake. The work also showed that when a sinter cake is considered to be a packed bed, the ''apparent'' diameters of the particles used for estimating gas flow resistance across the bed and heat exchange rates between gas and solid are different for the respective transport phenomena.
    A theoretical analysis of the magnitudes of forces acting on granules was made to identify the causes of the rearrangement of a bed during sintering.
  • Effect of Coexistence of Potassium and Sulphur on Abnormal Swelling during Reduction of Hematite Pellets

    pp. 642-649

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    DOI:10.2355/isijinternational.29.642

    In order to elucidate the effect of coexistence of potassium and sulphur on abnormal swelling during reduction of iron oxides, hematite pellets containing potassium carbonate have been reduced with sulphur bearing hydrogen base gas under the condition of gas starvation in the temperatures of 800 to 1 000°C.
    The addition of 0.12.0 mol% K2CO3 shows that normal swelling amounts to below 40% with macro- and microscopic cracks and that abnormal swelling reaches 300% at 800°C with coarse iron whiskers. This abnormal swelling due to only potassium takes place considerably regardless of any reduction history.
    The abnormal swelling due to gaseous sulphur is observed in range of 10-21 as sulphur activity of gas (aS) relative to Fe/FeS equilibrium. The maximum swelling is 500% with fine iron whiskers in aS of 0.1 at 900°C. It is found that sulphur has stronger abilities for the swelling than potassium.
    The largest swelling is 600% and it is observed under coexistence of potassium and sulphur without the formation of liquid phase at 800°C.
    Actions of both additives during metallization is discussed in the light of authors' previous researches dealing with the effect of sulphur on reduction of wustite.
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    3. Influence of Gaseous Sulfur on CO Reduction of Wustite Added with Foreign Oxides ISIJ International Vol.36(1996), No.8
  • Experimental Investigations on the Design of Gas Injecting Lances

    pp. 650-657

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    DOI:10.2355/isijinternational.29.650

    The influence of different lance lengths and diameters is studied experimentally on the upstream and downstream flow properties of gas such as stagnation and static pressure and the Mach numbers. Experimental results are presented and discussed in terms of the theory of compressible flow of gas for irreversible process of acceleration. The characteristic features of the above process of acceleration, i.e., loss in stagnation pressure, condition for choking and upstream static pressure are confirmed by the results obtained in this study. The implications of the above finding are discussed in relation to the design of lances for submerged gas injection practice.
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    3. Decarburization and Oxygen Absorption of Molten Iron of Low Carbon Concentration with Blowing Ar-O2 Mixture of Low Oxygen Pressure ISIJ International Vol.33(1993), No.8
  • Flow Phenomena and Heat Transfer around a Sphere Submerged in Water Jet and Bubbling Jet

    pp. 658-665

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    DOI:10.2355/isijinternational.29.658

    Velocity and turbulence around a sphere made of synthetic resin submerged in water and bubbling jets in a cylindrical vessel with bottom blowing were measured by making use of Laser Doppler Velocimeter (LDV). The melting process of an ice sphere was recorded by video camera. The local Nusselt number Nuθ of the ice sphere was determined from the initial change of the local radius. The mean Nusselt number Nu was calculated from Nuθ by numerical integration over the surface of the sphere. The effects of velocity and turbulence intensity on Nuθ and Nu were investigated. An empirical expression for Nu was proposed as a function of Reynolds number and turbulence intensity. A method of predicting the complete melting time of an ice sphere was presented.
  • Three-dimensional Elasto–Plastic and Creep Analysis of Bulging in Continuously Cast Slabs

    pp. 666-672

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    DOI:10.2355/isijinternational.29.666

    The bulging behavior of the solidified shell in continuously cast slabs have been numerically analyzed using the elasto-plastic and creep Finite Element Method. Three-dimensional model has been applied in order to investigate the effect of the narrow face shell on restraining the bulging deflection. Three-dimensional shell profile and temperature distribution in it have been determined using the segregation considered solidification analysis method. In this way, strains occurring at the solidification front near the narrow face of the slab, as well as those occurring in the broad face have been computed. The computed bulging deflection have been in good agreement with measurements, and the relationship between the strain caused by the bulging and the internal cracks have been investigated. In addition, the effect of the slab width on the bulging are discussed.
  • A Numerical Study on Cooling Process of Hot Steel Plates by a Water Curtain

    pp. 673-679

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    DOI:10.2355/isijinternational.29.673

    In order to predict the cooling process of a hot steel plate by a water curtain, the numerical model built up previously has been extended to the case where a horizontally fixed hot steel plate is cooled by a curtain dropping from a slit nozzle with a very large aspect ratio, because a number of similarities potentially present themselves betwen the water bar and the water curtain coolings. As a result, the numerical cooling curves calculated by the present modified model have been found to be in fairly good agreement with the experimental ones for various water flow rates.
  • Effect of Chromium Content on Creep Rupture Properties of a High Chromium Ferritic Heat Resisting Steel

    pp. 680-686

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    DOI:10.2355/isijinternational.29.680

    The effect of chromium content in the range of 10 to 13% on the mechanical properties has been investigated of a heat resisting steel for turbine rotors. It is revealed that increase in chromium content brings about increased amounts of dissolved chromium and the Cr2(C, N) type carbides, both of which enhance room temperature and elevated-temperature strengths. However, excessive addition of chromium to about 13% results in the formation of delta-ferrite, which is detrimental to creep rupture strength, especially on the long-term side. Thus, the optimum chromium content is considered to be at around 11.5%.
  • Improvement of the Torsional Properties of Drawn High Carbon Steel Wire by the Control of Pearlitic Microstructure

    pp. 687-694

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    DOI:10.2355/isijinternational.29.687

    An investigation was made on the diameter dependence of the critical drawing strain for the delamination of drawn high carbon steel wires, in comparison with the effect of a new patenting method. The new method, which was designed to retard pearlite transformation with the aid of high pressure, made it possible to obtain thick rods transfomed at the nose temperature as the thin rod patented conventionally. This method proved that the critical drawing strain for delamination did improve. Texture measurement showed the development of {110}‹110› and {110}‹114› cylindrical textures, and the deck of cards deformation mode was observed frequently in the wires patented by the new method.
    The relation between the texture change and the orientation relationship of pearlite is discussed.
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  • Analytical Procedure on Nozzle Flow of a Two-phase Mixture

    pp. 695-697

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    DOI:10.2355/isijinternational.29.695

  • Advances in Superplasticity and in Superplastic Materials

    pp. 698-716

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    DOI:10.2355/isijinternational.29.698

    Superplasticity and superplastic materials have gained considerable attention in recent years. The number of publications in these fields is increasing rapidly attesting to the current strong interest in these subjects. It can be stated that the technology of making complex shaped components by gas pressure techniques through use of superplastic sheet has come of age. On the other hand, bulk superplastic forming is still is its infancy. Considerable progress has been made in understanding the processes occurring in fine structure superplasticity and in internal stress superplasticity. Besides the traditional superplastic alloys based on nickel, titanium and zinc, new alloys have been developed which included microduplex stainless steel, aluminum–lithium and aluminum–magnesium alloys, mechanically allloyed aluminum, whisker and particle reinforced metal matrix composites, aluminum bronze and yttria-stabilized zirconia ceramic polycrystals.

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