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

Tetsu-to-Hagané Vol. 86 (2000), No. 11

  • Size and Shape of a Bubble on the Upper Surface of a Horizontal Plate of Poor Wettability

    pp. 709-716

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    Air was gradually supplied through a small vertical hole to form a single bubble on the upper surface of a horizontal flat plate of poor wettability. The bubble grew with an increase in the supplied air volume. The growing behavior of the bubble was observed with a CCD camera. The shape and size of the bubble on the upper surface of the plate were determined as functions of the surface tension, contact angle, densities of liquid and gas based on an energy equation for the bubble. Furthermore, the maximum bubble volume which allows a bubble to stay on the upper surface of the plate was predictable from the energy equation and a force balance equation for the bubble.
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  • Purification of Metallurgical Grade Silicon to Solar Grade for Use in Solar Cell Wafers

    pp. 717-724

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    A pyrometallurgical process for manufacturing solar grade silicon (SOG-Si) from metallurgical grade silicon (MG-Si) was developed. Metallic elements in MG-Si such as iron, titanium and aluminum, which show low partition coefficients, were removed by directional solidification practice. Phosphorus removal was carried out by evaporation for high vapor pressure, and boron was changed to boron oxide effectively by water vapor addition, because partition coefficients of phosphorus and boron are close to unity.
    To satisfy the impurity specification of SOG-Si, each purification process was combined as follows: (first process) dephosphorization by electron beam melting-first step directional solidification-(second process) oxidation of boron and carbon during plasma practice-deoxidation-second step directional solidification.
    MG-Si (purity level; 99 mass%) was successfully purified to the solar grade impurity level, that is, 6N (99.9999 mass%) except carbon and oxygen elements, by 20 kg scale and 150-300 kg scale equipments. The manufactured ingot was directly sliced to wafers and prepared to solar cells of multicrystalline silicon through the NEDO standard cell production process. The maximum conversion efficiency of solar cells attained to above 14%, which is almost equal to that of solar cells on the market.
  • Evaluation of the Quality of Low SiO2 Sintered Ore Considering Blast Furnace Operating Conditions with High Rate Pulverized Coal Injection

    pp. 725-732

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    In order to evaluate qualities of low SiO2 sinter such as reduction degradation behavior, reducibility and softening-melting properties, laboratory tests simulating in-furnace conditions at high PCI operation were carried out using three types of commercial sinters with varying SiO2 content.
    The main results obtained are as follows:
    (1) Under high PCI operating conditions, reduction degradation of sinter is decreased. This suppression is due to the shortening of retention time in a temperature range between 500 and 600°C by decreasing the heat flow ratio. This tendency of reduction in sinter degradation has been confirmed by operation trials at Fukuyama blast furnaces No. 3 and No. 4.
    (2) Hematite phase and micro pores increase with a decrease in SiO2 content of sinter, and consequently reducibility increases due to an improvement in reduction gas diffusion through the reduced layer.
    (3) The temperature at which softening commences and that at which the pressure drop rises are higher for low SiO2 sinter than the corresponding temperatures for high SiO2 sinter. This result suggests an improvement in the permeability of the cohesive layer in the blast furnace under high PCI operating conditions.
    (4) This evaluation has confirmed that low SiO2 sinter is superior to high SiO2 sinter as the blast furnace burden under high PCI operation even though the value of RDI is relatively high.
  • Mechanism of the Degradation of Coke Size in Raceway

    pp. 733-740

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    Experimental and theoretical studies were made to clarify the mechanism of the coke size degradation inside raceway and following results were obtained.
    (1) The mode of the coke breakage inside raceway was surface breakage and the fine generation rate could be estimated as the ratio of the impact energy on coke inside raceway and the fine generation energy per unit mass.
    (2) The impact energy charged on coke inside raceway could be calculated as the kinetic energy transfered from the blast to the coke particles through the hydrodynamic interaction and the fine generation energy could be estimated through drum tests as the ratio of the energy charged on coke in the drum to the amount of fine generated.
    (3) A mathematical model was developed with the help of the population balance theory usually used for comminution processes in the field of powder technology, which could predict not only the fine generation rate but also the coke size distribution inside raceway.
  • Acceleration of Copper and Tin Removal from Molten Steel by Decarburization under Reduced Pressure

    pp. 741-747

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    For accelerating the removal of copper and tin by evaporation under practical reduced pressure, 1.3×102 Pa, decarburization by weak oxidizing agents such as SiO2 and MgO has been investigated in laboratory scale experiments. The experimental results are as follows;
    (1) An effective removal of copper was obtained in the order of MgO>SiO2>O2 at a given amount of decarburization. The order is the same as that of oxygen potential of those oxidizers.
    (2) 50% of copper in iron melt was removed in 40 min in MgO crucible, which was reacted as an oxidizer. The rate of decopperization was 1.53 times higher than that without decarburization.
    (3) The reason why the acceleration of the removal of copper was achieved is assumed to be due to the increase in reaction interfacial area obtained by turbulence with decarburization. However, low oxygen content is preferable, because oxygen is the surface active element and is assumed to retard the evaporation reaction.
    (4) In high sulfur melt, 0.1 mass%, removal of copper was slightly lowered by suppresion of decarburization. However, removal of tin was accelerated. The phenomenon is considered to be caused by preferential evaporation as SnS.
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    3. Oxidative Removal of Cu from Carbon-saturated Iron via Ag Phase into B2O3 Flux ISIJ International Vol.52(2012), No.1
  • Effect of Stirring Condition and Bath Shape on Degassing Behavior in Water Model

    pp. 748-754

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    Degassing rate constant of CO2 in gas-stirred or mechanically stirred NaOH aq. system was studied by the water model experiments. Effects of stirring gas-flow rate, pressure of atmosphere, speed of rotor and shape of bath on rate constant, K, was investigated.
    The following results were obtained:
    (1) Rate constant, K, increased with increase of gas-flow rate, speed of rotor and with decrease of pressure of atmosphere. And K was correlated with stirring power ε and ε/A.
    (2) Calculated K using a single bubble model and surface reaction model showed a good agreement with observed K. Ratio of Ks at free surface to overall rate constant K was correlated with ratio of free surface area to volume.
    (3) Volumetric coefficient at free surface in RH shape was estimated three times as large as that in Ladle shape.
  • Explanation of Lubrication Behavior by means of Oil Film Measurement on Rolled Sheet Surface Measured by Fluorescence Method

    pp. 755-760

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    The photographs of workpiece surface illuminated with the UV light after rolling are taken by means of a fluorescence microscope with a camera. The workpieces having a smooth surface and a random rough surface are used in the experiments. The rolling tests are carried out changing rolling speed and viscosity of lubricant. The rolling oil containing some amount of fluorescence dye is used as a lubricant. The bright area is characterized by the lubricant pocket and the dark area by the asperity contact. From these photographs, the lubrication mechanism can be understood qualitatively. From the relationship between surface roughnesses of workpiece and roll, and inlet oil film thickness, the lubrication regime can be classified into the four regions which are the hydrodynamic lubrication, the hydrodynamic-boundary lubrication, the hydrodynamic-hydrostatic-boundary lubrication and the hydrostatic-boundary lubrication.
    Moreover, the visual light intensity produced by the fluorescence phenomena is measured by means of a fluorescence microscope with a ultra high sensitive CCD camera and an image processor. From the relationship between light intensity and oil film thickness, the oil film thickness distribution on the workpiece surface can be measured quantitatively.
  • Distortion in Service of a 1.2C-1Si-17Cr-2.5Mo-0.8V Tool Steel

    pp. 761-768

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    The effects of tempering temperature on distortion in service of a 1.2C-1Si-17Cr-2.5Mo-0.8V, mass%, tool steel which was developed for precision molding die of semi-conductors such as LSI were investigated. When tempered at 490°C after quenched from 1125°C followed by subzero treating, the steel possessed a very small distortion in service less than 1×10-5 under cooling-heating cyclic test, in accompany with a significant hardness above 62HRC. The small distortion in service was associated with an increase in retained austenite stability against the martensite transformation which was evaluated by lattice parameter of the retained austenite and its increment on tempering. It was expected that the stabilization of the retained austenite was resulted from dissolution of M3C carbides and suppression of M23C6 alloy carbide precipitation.
  • Effects of Grain Size and Aging Conditions on Fatigue Crack Propagation Behavior in Beta Ti-22V-4Al Alloy

    pp. 769-776

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    This paper presents the effect of microstructural modification on fatigue crack propagation (FCP) in a beta Ti-22V-4Al alloy. FCP experiments have been conducted using eight materials with different microstructures: two as solution treated materials (ST), three single aged materials (STA), and three two-step aged materials (STDA). Particular attention has been paid to the effect of grain size and aging condition. The results showed that in ST materials the coarse grained material exhibited higher FCP resistance than the fine grained material, but this grain size dependence was eliminated by aging, and two-step aging condition had very little influence on FCP behaviour. After allowing for crack closure, the effect of grain size was largely diminished and FCP behaviour was not affected by solution treatment temperature and aging condition. ST materials indicated the highest apparent and intrinsic FCP resistance and then STDA materials, STA materials in the decreasing order. Taking into account the difference in the modulus of elasticity in addition to crack closure, the difference in FCP resistance between STDA and STA materials was eliminated, but ST materials still showed higher FCP resistance.
  • Acceleration of Superlong Fatigue Failure by Hydrogen Trapped by Inclusions and Elimination of Conventional Fatigue Limit

    pp. 777-783

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    The mechanism for fatigue failure in extremely high cycle fatigue in the regime of N>107 is discussed. A special attention was paid to a newly found particular fracture morphology in the vicinity of fracture origin (subsurface nonmetallic inclusions) of a heat treated Cr-Moalloy steels (Specimen QT). The particular morphology looks a dark area inside fish-eye mark by optical microscopic observation. Specimens with short fatigue life of the order of Nf=105 do not have such dark area, ODA (optically dark area), in fish-eye. To investigate the influence of the hydrogen trapped nonmetallic inclusions on fatigue properties, specimens quenched in a vacuum (Specimen VQ) were prepared. Specimens VQ contained 0.01 ppm hydrogen and on the other hand QT 0.7-0.9 ppm hydrogen. Specimens VQ had much smaller ODA than Specimens QT. Hydrogen was detected by Secondary Ion Mass Spectrometry at the inclusion at fracture origin of Specimens QT but not at the inclusion of VQ. Thus, it can be concluded that the formation of ODA is closely related to hydrogen trapped by nonmetallic inclusions. The predictions of fatigue limit by the √area parameter model are approximately 10% unconservative for fatigue limit defined for 107 cycles. However, if we consider the area of ODA into the fatigue limit estimation, the √area parameter model can successfully predict the fatigue limit very accurately.

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