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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 64 (1978), No. 10

  • Heat Transfer Coefficient between Wall and Particles Bed in Rotating Cylinder

    pp. 1491-1498

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    The heat transfer coefficient between a rotating cylinder wall and the spherical particles bed contacting with it was experimentally and theoretically studied. Two experiments were done: one in the steady condition with a constant feed of solid particles and the other in the transient condition with initially charged burdens. In the both experiments the steel cylinder assumed to be a rotating kiln was externally heated by means of Kanthal wire, which had been wound on the cylinder wall. The temperature was limited to a lower range in which radiation could be neglected. Wall, particles bed and free board temperatures were continuously measured by means of CA-thermocouples. Steel, glass, copper and alumina balls, 0.03 cm to 0.4 cm in size, were used as the solid burden.
    Heat transfer coefficients between the wall and the particle bed which have been estimated in analyzing the measured temperatures can be explained by the thermal penetration model
  • Changes of Mineral Phases during the Sintering of Fe2O3-CaO-SiO2 System

    pp. 1499-1508

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    Mixtures of fine powders with the basicities from 0.6 to 5.0 consisting of hematite (80%), slaked lime, and quartz were heated rapidly to 900-1400°C and cooled in air. The process of mineral formation of them during the rapid heating was examined.
    At about 950-1000°C, calcium ferrite was formed and caustic lime originated from slaked lime was consumed completely. At the temperature lower than 1 150°C, quartz hardly reacted with other minerals such as hematite, caustic lime, and calcium ferrite. Thus, their microstructures changed, independently of their basicities, into those consisting of primary hematite, calcium ferrite, and quartz.
    At the temperature higher than about 1 160-1180°C, calcium ferrite melted and reacted with quartz. By this reaction, characteristic microstructures were formed according to their basicity. The microstructure of mixtures with the basicity lower than 1.6 consisted of glassy silicate and secondary hematite originated from calcium ferrite. The microstructure of mixtures with the basicity higher than 2.0 consisted of calcium ferrite and dicalcium silicate.
    On the basis of the above results, the microstructures and their formation processes of iron are sinters with various basicities were discussed.
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    Readers Who Read This Article Also Read

    1. Heat Transfer Phenomena in Immersion Cooling of Heated Steel Plate and Influence of Water Stirring on Heat Transfer Tetsu-to-Hagané Vol.64(1978), No.1
    2. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    3. 第95回講演大会討論会講演概要 Tetsu-to-Hagané Vol.64(1978), No.2
  • Analysis of CO Reduction of Hematite Pellets in an Isothermal Fixed Bed by Multi-interface Model

    pp. 1509-1517

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    Reduction experiments of hematite pellets with CO in an isothermal fixed bed were carried out under various experimental conditions. The pellets used were made of pyrite cinder and their porosity was approximately 15%.
    The equation of continuity for CO reduction of pellets in an isothermal fixed bed was numerically solved by the application of the multi-interface model to describe the reduction rate of the pellets where parameters obtained previously by the technique of step-wise reduction of the pellets were used. Agreement between the calculated curves and observed data was satisfactory.
    In the experiments it was observed that pellets in the vicinity of the tube wall were reduced more or less rapidly than in the central part of the tube. The wall was found, however, to have a small effect on the calculated results of the average fractional reduction of the bed and exit gas concentration.
  • Analysis of CO Reduction of Hematite Pellets in an Isothermal Moving Bed by Multi-interface Model

    pp. 1518-1527

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    The CO reduction of hematite pellets in an isothermal moving bed was studied theoretically as well as experimentally.
    Various models for the process analysis of the isothermal moving bed were constructed for the steady and the unsteady state by regarding or disregarding the wall effect. The rate equation based on the multiinterface model and the rate parameters determined by the technique of step-wise reduction of a single hematite pellet were used in the analysis.
    The results are summarized as follows;
    1) It was found that the multi-interface model with rate parameters obtained by step-wise reduction may be used for the process analysis of a moving bed reactor.
    2) Calculated results based on the models in which the wall effect was properly taken into account showed agreement with experimental results as to exit gas composition and the axial distribution of fractional reduction.
    3) The wall gave noticeable effects on the exit gas composition at higher descending velocity of the pellets and on the axial distribution of fractional reduction at lower descending velocity.
    x

    Readers Who Read This Article Also Read

    1. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    2. On the Primary Cooling in Continuous Casting Tetsu-to-Hagané Vol.45(1959), No.12
  • On the Desulfurization of the Molten Metal in an Open Ladle Stirred by an Impeller Modified by Gas Injection

    pp. 1528-1537

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    In order to enhance the dispersion of desulfurizing agents into hot metal, the injection of nitrogen gas has been used together with the revolutional stirring by an impeller of a gate type. At the both ends of the impeller, a nozzle is embedded and used for the injection of nitrogen gas into hot metal toward the direction opposite to the movement of the impeller.
    Water model experiments show that the gas injected efficiently breaks up a cone shaped agglomerate of desulfurizing agents at the bottom of the rotational vortex formed around the impeller shaft and makes it disperse homogeneously into the bath. This suggests that the chemical efficiency of desulfurization will be improved to a greater extent than that without the gas injection.
    The plant scale equipment has been constructed to desulfurize 60t of hot metal in a ladle. Under the condition of 77 rpm in revolution rate and 3 Nm3/min of nitrogen gas, sulfur content of 0.05% is reduced to 0.012% after the treatment of 1 1 min with calcium carbide of 3kg (75% in purity) per ton of hot metal.
    The observed rate of desulfurization is reasonably interpreted in terms of the rate controlled by sulfur transfer in hot metal.
  • Optimizing Sulfide Shape Control in Large HSLA Steel Ingots by Treating the Melt with Calcium or Rare Earths

    pp. 1538-1547

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    Solute segregation, constitution and distribution of sulfides in Ca-treated compared with RE-treated HSLA steel ingots have been investigated as a function of the concentration of Ca, RE, S and O. Characteristic S-segregation pattern including bottom cone sedimentation of sulfides is found to disappear at [%Ca] · [%S] 0.28≤1×10-3 in Ca-treated ingots and at [%RE] · [%S] ≤1×10-4 in RE-treated ingots. The disappearence is named “S-reversal”. These features are reasonably interpreted on the basis of the model proposed earlier to account for the “S-reversal” in RE-treated ingots.
    The degree of sulfide shape controlling with Ca or RE can favourably be evaluated in terms of atomic concentration ratio, ACR, of effective Ca or RE to S in the melt in mold. Sulfide shape control is in complete throughout the ingots at ACR of 0.2, satisfactory at 0.4 except for A- and V-segregates, then becomes complete even in the segregates at 1.8. By controlling the concentration of Ca or RE and S to fall within the area bound by ACR≥1.8 and [%Ca] · [%S] 0.28≤1×10-3 or [%RE] · [%S] ≤1×10-4 on Ca or RE vs S coordinates, HSLA steels that are totally free from hydrogen induced cracks have been produced for sour gas service.
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    Readers Who Read This Article Also Read

    1. Mechanism of Sulfide Shape Control in Continuously Cast HSLA Steel Slabs Treated with Ca and/or RE Tetsu-to-Hagané Vol.66(1980), No.3
  • Development of a Carbon-free Casting Powder for Continuous Casting of Steels

    pp. 1548-1557

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    The carbon particles are contained in conventional casting powders to control the fusion rate of the powders. They have been found, however, to give rise to the surface carburization of continuously cast stainless steels when solidified shells come in contact with carbon concentrated slag layers. On the other hand, fine boron nitride particles, like carbon particles, have been found to be able to adjust the fusion rate of casting powder without causing the surface carburization. Thus, the carbon free casting powder using sintered granular particles as basic particles and BN particles as skeletons has been developed.
    Application of the carbon free powder to continuous casting of stainless steel blooms has resulted in excellent castability and surface condition, completely preventing the surface carburization.
  • On the Weathering Mechanism of LD Converter Slag

    pp. 1558-1567

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    In order to elucidate the weathering mechanism of LD converter slags, the actual slags were exposed to air as well as water and autoclaved. The behaviors of disintegration, mineral phases and reaction products of slags were mineralogically examined. Various factors which affect disintegration were also discussed. Results obtained are as follows:
    (1) LD slag mainly consists of five mineral phases, namely dicalcium silicate, tricalcium silicate, lime, wustite and dicalcium ferrite. Two types of lime in precipitating state are observed. One is a large cluster with the order of milimeter in size, and the other is a small dispersion with tens of micron.
    (2) Disintegration of slag is closely related to the amount, distribution and characteristics of the lime phase in slag. The higher in free lime content, the more disintegration is, but when the slag contains less than 1% of free lime, it hardly disintegrates. Divalent oxides, FeO and MnO, dissolved in lime phase also restrain disintegration.
    (3) The volume expansion by hydration of lime is a main cause of weathering and disintegration of slag. Silicates on surface also hydrate, but don't result in disintegration.
    (4) Accordingly, to use steelmaking slag for raod and construction materials, an effect to decrease free lime in slag should be made.
  • A Metallurgical Study of Oxide-Base Slag Used for Electroslag Remelting

    pp. 1568-1577

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    The applicability of oxide-base slag were examined, because fluoride-base slag, usually used for electroslag remelting, sometimes accompanies fluorine emission during remelting. CaO-Al2O3-base slag were chosen and remelting were carried out by furnaces with 80 mm in diameter and with 360 mm. Operational characteristics and qualities of ingot were assessed in comparison with fluoride-base slag. Results obtained are as follows:
    (1) There is no trouble in operation with oxide-base slag with no fuming and good electric stability.
    (2) Tendency to form heterogeneous slag skin is improved by a small addition of CaF2.
    (3) Behaviors of elements are little affected with oxide-base slag because of the low activity of iron oxide in slag. Furthermore, excellent deoxidation and desulphurization are attained.
    (4) Because oxide-base slag has a small partition ratio of hydrogen, (H) J [H], remelting must be carried out more carefully to the moisture of slag. During remelting, however, the effect of the moisture in atmosphere is a little because of small transfer coefficient of hyrogen through gas-slag interface.
    (5) Power consumption decreases about 20-40% with oxide-base slag. Accordingly, it may be possible that CaO-Al2O3-base slag takes the place of fluoride-base slag.
  • The Extension of Hydrogen-Induced Fracture in Linepipe Steels

    pp. 1578-1587

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    The hydrogen-induced fracture of linepipe steel is characterized by the formation of internal blisters caused by hydrogen precipitation at an inclusion-matrix interface, followed by the formation of blister-crack array by linking the region connecting them under the combined action of internal hydrogen pressure and external force.
    The manner of extension of the hydrogen-induced fracture of this type is considerably influenced by the presence of external force, i. e., in the absence of it the fracture develops by stepwise linking the blisters. while in the presence af it the fracture develaps by linking the blisters which are formed in stacked arrays out of the plane approximately perpendicular to the external stress axis. The shear stress distribution induced around the blister is sensitively influenced by external force applied parallel to the blister. therefore it is expected that the manner of extension of the blister-induced fracture should be influenced by the external force.
    In the present paper the above-mentioned change due to external force of the manner of extensi the hydrogen-induced fracture is explained on the basis of the stress analysis around the hydrogen gas pressurized crack-like cavity under stress.
  • Tensile Properties of Hastelloy X and Incoloy 800 Exposed to Air and Helium at High Temperature

    pp. 1588-1597

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    The effect of corroded surface layer on the tensile properties at room and high temperatures was studied for Hastelloy X and Incoloy 800 by comparing the properties of corroded specimens with those of aged specimens. Corroded specimens were those subjected to 3000-h and 50000-h exposures at 1000°C to air and VHTR helium. A small effect of exposure was observed both to helium and air in the case of Hastelby X. In the case of Incoloy 800, however, exposure to air was found to reduce tensile properties markedly whereas exposure to helium scarcely reduced. Metallographic observation indicated that reduction of tensile properties was caused by intergranular oxidation. The ratio of the tensile strength (corroded specimen/aged specimen) being plotted against the amount of intergranular oxidation, data of the two alloys were superimposed on the same curve. Ductility minimum point observed on the solution treated materials at intermedate temperature was not detected on the aged and the corroded Hastelloy X, but was detected on the aged and the corroded Incoloy 800.
  • Improvement of Hardenability of Steel with Al-B by Double Quenching

    pp. 1598-1606

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    Hardenability increasing effect due to B was studied for low alloy steels treated with Al-B (0.06-0.08% Al-0.0010%). The quench hardenability was found to be markedly improved by double quench. The mechanism of the increased quench hardenability by the double quench was studied by means of a fission track etching technique. It was shown, in the double quench, that a quenching from 1000°C for 1 h prior to the 2nd quench gave rise to excellent hardenability which could not be attained by a single quench. The role of the 1st quench is to obtain the optimum amount of soluble B in matrix. A combination of the Al-B treatment and thet double quench is a reliable method to maximize the hardenability increasing effect of B in low alloy steels.
    x

    Readers Who Read This Article Also Read

    1. Heat Transfer Phenomena in Immersion Cooling of Heated Steel Plate and Influence of Water Stirring on Heat Transfer Tetsu-to-Hagané Vol.64(1978), No.1
    2. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    3. 第95回講演大会討論会講演概要 Tetsu-to-Hagané Vol.64(1978), No.2
  • Microsegregation of Chromium and Carbon and Ridging Phenomenon in 18Cr Stainless Steel Sheets

    pp. 1607-1614

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    Hot-rolled sheets of 18% Cr stainless steel having dual structures of ferrite and transformed (martensitic) phases were made by water quenching from an temperature in (α+γ) region, 1200°C. The effect quenchphases were made by water quenching from an temperature in (α+γ) region, 1200°C. The effect of the microsegregation of Cr and C on ridging phenomenon was examined using the material annealed with various conditions. The following results were obtained.
    (1) Even after the annealing at 800°C for 20h the segregation of Cr which was rich in ferrite phase and poor in prior austenite phase was observed.
    (2) Carbon was high in prior austenite phase and was decreased with annealing time.
    (3) Precipitation of chromium carbide by annealing was observed much in prior austenite phase.
    (4) The carbides were distributed locally in the material even after cold rolling and annealing.
    (5) Intensity of ridging was independent on the changes in structure and hardness due to annealing.
    (6) The relation between spacings of ridge and of the microsegregation of Cr and C was recognized for small ridges observed at the surface of the specimen, but was not clear for large undulations of ridging.
  • Proposals of Hot Blast Stove Design

    pp. 1615-1621

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    A new system of fixing the temperature of hot blast for a blast furnace is proposed. This new system is composed of two or more hot stoves and a temperature equalizer which is a heat accumulator filled with checker bricks. The hot blast from a hot stove, whose temperature changes with the lapse of time, is passed through the temperature equalizer.
    The hot blast temperature at the exit of the temperature equalizer was calculated in several cases, and the result shows that it can be maintained nearly equal to the average value of the hot blast temperature at the exit of hot stove, as obtained by the staggered-rap-parallel operation.
    The second proposal is that the heat transfer coefficient of an ordinary Freyn type checker brick can be increased by 2 to 2.6 times by means of setting reduced inner diameter sections at the gas passages.
    By using these newly designed checker bricks, the fuel gas consumption can be remarkably saved and it becomes possible to obtain the desired hot blast temperature with lower combustion gas temperature.
    x

    Readers Who Read This Article Also Read

    1. Heat Transfer Phenomena in Immersion Cooling of Heated Steel Plate and Influence of Water Stirring on Heat Transfer Tetsu-to-Hagané Vol.64(1978), No.1
    2. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    3. 第95回講演大会討論会講演概要 Tetsu-to-Hagané Vol.64(1978), No.2
  • Solubility of Tungsten in Nickel-Rich Ni-Cr Alloys at 1000°C

    pp. 1622-1624

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    For the determination of solubility of tungsten in nickel-rich Ni-Cr alloys at 1 000°C, five specimens of multi-phase Ni-Cr-W alloys with different composition were equilibrated for more than 2000h and the chemical composition of each phase in the specimens was analyzed by means of the electron probe microanalysis. The result was summarized as an isothermal section of the Ni-Cr-W equilibrium diagram, in which a three phase triangle composed of γ, α2 and σ phase was identified.
  • The Automation of Mechanical Property Testings in Steel Industry

    pp. 1625-1637

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  • Smelting and Thermodynamics

    pp. 1638-1643

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  • 抄録

    pp. 1644-1648

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