Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 78 (1992), No. 3

  • The Recent Trend of Steel Products for Automobile

    pp. 339-345

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  • Recent Trends in High Strength Stainless Steel

    pp. 346-353

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  • Gas Diffusion Electrode

    pp. 354-359

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  • Pyrolyzed Products of Coal Rapidly Heated on a Molten Slag

    pp. 360-366

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    Behavior of rapid pyrolysis of coal is of considerable importance in understanding an early stage of post combustion in an iron are smelting reduction converter.
    Products by pyrolysis of various kinds of coal under conditions of high heating rate and high temperature on a molten slag have been studied quantitatively.
    By analyzing the pyrolysis products such as gas, tar and residual char, data were obtained as a function of coal rank(eleven coals and one metallurgical coke), temperature(13501500°C), gas residence time(2.510 s), and coal diameter(0.87.0 mm) in the experiments using high frequency induction furnace.
    Total coal volatiles released in these experiments increased by 10 to 20% compared to the proximate volatile matters. Carbon oxide gas(CO+CO2) and hydrocarbon gas (CH4-C3H6) yields increased with increasing [O] content and [H]/[C] atomic ratio in parent coal, respectively.
    The effect of coal diameter and slag temperature on total volatiles did not become significant.
    The ratio of [S] and [N] retained in residual char to total [S] and [N] contained in parent coal decreased with increasing volatile matter of coal. Normalization of the data, by taking the ratio of [S] and [N] released to total volatiles released, indicated that [S] and [N] in all coals examined were preferentially retained in volatiles and showed the maximum retention at around [C]daf=85% coal.
  • Mechanism of Heat Transfer in Smelting Reduction with a Thick Layer of Slag

    pp. 367-374

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    High efficiency of heat transfer has been obtained in a smelting reduction furnace which has an essential feature of a thick layer of slag coexisting with carbonaceous materials, when stirring intensity by bottom bubbling is higher than 2 kW/t-metal.
    Heat transfer mechanism in this process has been examined both theoretically and experimentally.
    (1) Heat transfer by radiation and gas convection was calculated by using a mathematical model and was compared with actual data. This model was constructed by dividing the furnace into three regions depending on the modes of reaction and heat transfer and by taking the mass and heat balances over each region. When the gas temperature is as high as 2170°C, the actual heat transfer can be explained mainly by radiation. But, under practical conditions (gas temperature≤1765°C), the contribution of radiation and gas convection to heat transfer is only 20-30%.
    (2) In order to explain the heat transfer when the temperature of exhaust gas was relatively low, the heat transfer by circulation of super-heated carbonaceous material was assumed. The assumption coincides with other data on the reducing reaction and on the combustion in the smelting reduction.
  • Aluminium-Oxygen Equilibrium between CaO-Al2O3 Melts and Liquid Iron

    pp. 375-382

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    Aluminium-oxygen equilibria between CaO-Al2O3 melts and liquid iron were studied in the temperature range of 1823 to 1923 K, using alumina and lime crucibles. The equilibrium constant K for the reaction: 2Al+3O=Al2O3 was discussed with reference to the supersaturation for nucleation of alumina, and compared with the previous experimental and thermodynamic data. The supersaturation was observed in the experiments in which an Fe-Al alloy with low concentrations of initial oxygen was used under the condition of no stirring. Supersaturation increased with a decrease of oxygen content in liquid iron. Two types of alumina inclusions with a size of 25 μm and below 0.1 μm were observed by SEM.
  • A. C. Impedance Analysis of the Kinetics of Reactions between Molten Cu or Fe and CaO-Al2O3 Slag

    pp. 383-390

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    A chemical reaction at the interface between slag and metal can be analyzed as a kind of electrode reaction because of the ionic nature of liquid slag.
    In the present work, application of an A.C. impedance method to slag-metal reaction in iron- and steelmaking process was tried to clarify the individual kinetic factors concerning the electrode reactions at the interface between slag and metal. The total impedance between CaO-Al2O3 slag and Cu-S or Fe-C-S melts was measured in this paper.
    The results obtained were successfully used to determine the individual factors on kinetics of the electrode reaction between slag and metal, such as solution resistance of slag, interfacial capacitance in electric double-layer, overvoltage of charge transfer, rate constant and so on. In each component of Faradaic impedance, ZF, relating to the electrode reactions at the interface between slag and metal, which were estimated by the parameter fitting, the magnitude of charge-transfer resistance, RC, was about 1/2 to 1/5 of that resistant component in reaction or crystallization impedance with diffusion, RR, for the anodic and cathodic reactions in both systems.
  • Determination of Oxygen Activity in Molten Steel by Using Oxygen Sensor of which Partial Electronic Conduction Parameter Determined

    pp. 391-398

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    Partial electronic and holic conduction parameters, Pe', and Ph, of a solid electrolyte for an oxygen sensor were determined by a developed AC bipolar procedure. Both parameters of ZrO2-8 mol% MgO solid electrolytes produced by Japanese different producers are as follows:
    log Pe'(with atm unit)=-85000/T+29.2±1.0
    log P·h(with atm unit)=27000/T+13.3±0.8
    No different parameter among the solid electrolytes produced by the Japanese different producers is observed.
    An oxygen activity in molten steel was observed by using an oxygen sensor constituted by the solid electrolyte of which the partial electronic conduction parameter was determined. If the sensor was swung in the molten steel then the oxygen activities observed were consistent with those estimated on the basis of an equilibrium between Al and Al2O3.
  • Estimation of Viscosities of Liquid Alloys

    pp. 399-406

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    The effects of composition and temperature on viscosities of liquid metals have been studied by systematical analysis of data from the literatures in order to estimate the viscosities of liquid alloys. The viscosities of liquid alloys are expressed by the following equations:
    η=A exp (B/RT) [mPa·s]
    A=1.7×10-4ρ2/3Tm1/2M-1/6/exp(B/RTm) [mPa·s]
    B=2.65 Tm1.27 [J·mol-1]
    where ρ is the density of alloy [kg·m-3], Tm is the absolute temperature of liquidus [K], M is atomic weight [kg·mol-1], and R is gas constant [8.3144 J·mol-1·K-1]. Calculated values from the above equations for the viscosities of various liquid binary alloys were in good agreement with their experimental data from the literatures. Using these equations, it will be possible to estimate viscosity for any liquid alloy at any temperature.
  • Behavior of Hg-Air Vertical Bubbling Jet in a Cylindrical Vessel

    pp. 407-414

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    Gas holdup α and bubble frequency fB in mercury-air vertical bubbling jet in a cylindrical vessel were measured by means of an electro-resistivity probe. On the basis of the present and previously published experimental results, correlations for α, fB and mean bubble rising velocity uB were derived as functions of injected gas flow rate Qg and nozzle diameter dn. These correlations are valid in the vicinity of nozzle exit where the expansion of gas due to static pressure change is negligible. Furthermore, correlations for α, fB and uB applicable to bubbling jets with density ratio ρlg between about 800 and 12000 were proposed as functions of Qg, dn and ρlg, where ρg is the density of gas and ρl is the density of liquid.
  • Heat Transfer between Bubbles and Liquid during Cold Gas Injection

    pp. 415-422

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    In the steelmaking and some other metal refining processes, bottom gas blowing is a popular method. In these systems, gas is blown into high temperature liquid metal from the bottom of the vessel at a temperature lower than the liquid temperature. Therefore, heat transfer takes places between bubbles and liquid. The mechanism of the heat transfer and the effect of the heat transfer on the formation of bubbles and the rising characteristics of the bubbles were investigated using air and helium in water model. The temperature of the injected gas was about -110°C. Heat transfer between bubbles and liquid almost finished near the nozzle. Bubble expansion due to the heat transfer resulted in the gas holdup increase in the radial direction. In the field far from the nozzle, the bubble characteristics for cold gas injection was the same as that for ambient temperature gas injection at the same mass flow rate.
  • Model Experiment on the Motion of Fine Particles of Inclusion in Liquid Steel

    pp. 423-430

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    The lateral migration of solid particles in the vertical pipe flow of water was studied to know the behavior of fine particles of inclusion in the flow of liquid steel. Hollow glass particles, 0.46×103 kg/m3 in density and 55135 μm in diameter, were injected in a vertical pipe flow of water or aqueous glycerol solution, and the collection efficiency of particles on the wall, η, was measured at the exit of the pipe. Most experiments were carried out for the case of upward flow, and effects of various factors on η were investigated in the following experimental conditions:z=0.251 m, vf=0.010.5 m/s, dP=55135 μm, μ=10-33.7×10-3 Pa·s, D=0.02, 0.033 m, where z is pipe length, vf mean velocity of liquid, dP particle diameter, μ viscosity of liquid, D diameter of pipe.
    Rubinow and Keller's equation on migration velocity of a rotating sphere in a uniform shear flow was modified by multiplying a correction factor, β and then values of η were calculated by the trajectory model. Comparing the calculated and observed values of η, the values of β were determined and correlated with the particle Reynolds number and the tube Reynolds number. By using this correlation, values of η of alumina particles in liquid steel were estimated for various conditions.
  • Mechanism of Separation of Inclusions from Molten Steel Stirred with Rotating Electro-magnetic Field

    pp. 431-438

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    An experimental model was constructed to clarify the mechanism of separation of inclusions from molten steel strongly stirred with a rotating electro-magnetic field.
    Molten steel was rotated and solidified in a crucible. The ingot obtained had its maximum oxygen content at the axis of rotation. The existence of this maximum area can be partly explained by the centripetal force acting on inclusions during rotation of the molten steel.
    Many coagulating inclusion pairs were observed in the ingot, with the radii of the inclusions forming coagulating pairs being concentrated in the range from 10 to 50 μm. This phenomenon was explained using Saffman's model, which shows the probability of gradient collision between inclusions in turbulent eddies. This inclusion coagulation effect suggests the high deoxidation capability of rotating molten steel in an electro-magnetically stirred ladle.
  • A Hidrodynamical Analysis of the Molten Steel Flow in the Continuous Casting Mold

    pp. 439-446

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    Mold powders are easily entrapped in the molten steel and become one of the main sources of the troubles such as frange cracks in DI cans. It is important to know how the mold powders are entrapped and how to aviod these. In order to clarify the phenomena, a hydrodynamical analysis which treated the molten steel flow from the tundish to the mold has been made. The results of such an analysis were checked by some tests which were accomplished by a water model and by the YAWATA No. 3-CC plant. This can be concluded as follows:
    (1) The analytical surface velocities and experimental ones show a good fit.
    (2) The analytical surface velocities can be used as one of the most useful quality control parameters to classify the grades of the products.
  • Model Experiment and Theoretical Analysis for the Effect of Electromagnetic Pressure on Surface Quality of Continuous Castings

    pp. 447-454

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    Being aimed to improve the surface quality of a continuously cast steel, a new electromagnetic casting method is proposed where the high frequency magnetic field is imposed on the initial stage of solidification from the outside of a mold. The magnetic pressure induced by the magnetic field provides the solidification taking place under the soft contacting pressure of molten metal with the mold, so called soft contacting solidification. Molten tin was cast by imposing magnetic field with 1.75, 3.75 and 15.4 kHz frequency in order to examine the applicability of the method to the cast of steel. It is found that this electromagnetic casting method has a potential to be applied to the cast of steel. The stronger intensity of magnetic field could provide the better surface quality of products in the way of reducing oscillation marks. However, the excess intensity of magnetic field caused the disturbance on meniscus inducing surface defects. The critical intensity of magnetic field at which the surface defects due to fluid disturbances at meniscus appeared increased with increasing the frequency of magnetic field. It is noticed that the effect of magnetic field on reduction of surface defects appears more significantly when mold oscillation was not applied than when the oscillation was applied.
  • Shape Control of Molten Metal Puddle by Directly Imposing Electric Field in the Casting Direction and Magnetic Field between Rolls in Twin Roll Process

    pp. 455-462

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    A new process to control the side edge shape of molten metal puddle is proposed in which direct electric field imposed in the casting direction and direct magnetic field applied between rolls induce electromagnetic force in molten metal puddle. The experimental works were carried out to clarify the possibilities of holding molten metal at side edge and of controlling the side edge shape by the electromagnetic force. It was found that the holding height of meniscus can be controlled by the direct electric current as an operating parameter. This method to hold molten metal at side edge is named an electromagnetic dam. And it was noticed that, at the same time, the saw shape edge on cast sheet, which is attributed to the instability of meniscus, becomes smooth by the function of electromagnetism. This effect stabilizing the edge shape was explained qualitatively by considering the characteristics of electromagnetic force. The experimental data verified the mathematical model of the electromagnetic dam which can predict the holding height of meniscus position of molten metal puddle from electric current and magnetic field.
  • Determination of Ultra-low Content of Carbon in Steel by Infrared Absorptiometry after Combustion in Electro Resistance Furnace

    pp. 463-468

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    An analytical method has been developed in order to determine ultra-low content of carbon in steel. In the method the specimen is heated up with relatively slow speed in electro-resistance furnace and the infrared spectrum detector has been linked with data analyzer, so that the combustion behavior of carbon has been able to be detected and analyzed in real time.
    By the method CO2 originated from carbon adsorbed on the surface of a specimen can be separated from CO2 taken rise from carbon in the specimen.
    Thus less than 10 ppm of carbon in steel can be analyzed rapidly with high precision.
  • The Structure and Properties of Electrolytic Chromate Film Formed in CrO3-Co2+-Cl- Bath on Zn and Zn-Ni Alloy Plated Steel Sheet

    pp. 469-476

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    Relation between the structures of chromate films, formed by electrolytic reduction in CrO3-Co2+-Cl- and CrO3-SO42- bath on Zn and Zn-Ni alloy plated steel, and characteristics has been investigated. The structure of chromate film formed in CrO3-Co2+-Cl- bath is amorphous and a little Cl is uniformly distributed in the film.
    The film is mainly composed of Cr(OH)2, Cr2O3, a lot of Cr6+, and only a little Zn2+, not containing Cr. When the film is formed, Zn2+ dissolution rate in chromate bath is affected by Zn and Zn-Ni alloy plated steel sheet, and then dissolved Zn2+reacts with Cr6+in the film to reduce Cr6+and simultaneously produce Cr3+ in the film. Co2+ CrO3-Co2+-Cl-bath suppresses the dissolution of Zn2+, and so component of the film formed in the bath is stabilized. Furthermore, materials chromated in the bath show excellent corrosion resistance, because much Cr6+ in the film repairs defects of surface. Cr(OH)3 in outer layer of film affects paint adhesion. The more Cr(OH)3 is, the better paint adhesion becomes.
    It is necessary that chromated materials secure stabilized properties as the results of controling Zn2+ dissolved from materials. In the case of chromating in CrO3-Co2+-Cl-bath, Zn2+hardly dissolves in chromarte film.
  • In-situ TEM Observation of Spheroidization Behavior of Cementite in Medium Carbon Steels

    pp. 477-484

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    The spheroidization treatment for medium carbon steels has been usually performed by annealing just above Al temperature and slow cooling.
    In this study, the spheroidization behavior of cementites in the steel was in-situ observed by ultra-high voltage electron microscopy, in order to investigate the effect of initial microstructure on the spheroidization behavior. Two microstructures, i. e. fine ferrite-pearlite and bainite, were selected as the initial microstructure for the treatment, and were prepared by thermo-mechanical treatments.
    By continuous observation, following results were obtained. Re-austenitization occured at colony and grain boundaries in ferrite-pearlite structure. In the case of bainite, it occured in the vicinity of small cementite particle which distributed homogeneously in ferrite grain. Furthermore, substructures were formed by re-arrangement of dislocations.
    During cooling, coalescence of austenite grains occured. Based upon the observation of this behavior, discussion was focused on the role of internal stress caused by eigen strain due to transformation.
  • Effect of Deformation Rate on the Small Punch Ductile-Brittle Transition Behavior in Turbine Rotor Steels

    pp. 485-492

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    The effect of deformation rate on the ductile-brittle transition behavior of temper embrittled turbine rotor steels has been investigated employing a newly developed dynamic small punch (SP) tester. It is shown that the dynamic SP test produces a clear ductile-brittle transition behavior similar to the Charpy V-notch (CVN) impact test. The ductile-brittle transition temperatures determined by fracture energy measurements and by fracture surface observations are higher about 48-90°C than those obtained from the static SP tests. The effect of deformation rate on the relationship between FATTSP and FATTCVN obtained from SP and CVN tests is examined: it is found that as the deformation rate increases to 103 and 2.5×106 times, the value of a, which is a proportionality coefficient in the relationship given by FATTSP=α×FATTCVN, is increased to 0.45 and 0.54, respectively.
    From these experimental results, it is implicated that the use of the dynamic SP testing method enhances the predictability of FATTCVN.
  • Effect of Bi-modal Microstructure on Fracture Toughness of Ti-15V-3Cr-3Sn-3Al Alloy

    pp. 493-499

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    Effect of bi-modal microstructure on fracture toughness of beta type Ti-15V-3Cr-3Sn-3Al alloy was systematically examined. Bi-modal microstructure that was obtained through combination of aging at high and low temperatures after solution treatment is composed of coarse and fine alpha precipitates and beta matrix. This bi-modal microstructure improves fracture toughness-strength balance compared with microstructure produced by aging at single temperature after solution treatment. Comparing at the same strength level, increase of volume fraction of the coarse alpha precipitated by aging at 873 K in the bi-modal microstructure gives higher fracture toughness, however, it reduces attainable strength. Homogeneous distribution of coarse alpha precipitates obtained by pre-aging at 573 K before aging at high temperature tends to reduce the superiority of the bi-modal microstructure in fracture toughness. This superiority is provided by the formation of voids and microcracks in the coarse alpha precipitates and rugged crack propagation due to the uneven microstructure.
  • Observation of Inner Fibers in Metal Matrix Composites by X-ray Computed Tomography Using Synchrotron Radiation

    pp. 500-507

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    Direct observation of the reinforcing fibers was attempted by X-ray Computed Tomography (CT) using synchrotron radiation in the Photon Factory of the National Laboratory for High Energy Physics (KEK) in Tsukuba. The energies were selected 21 and 29 keV for aluminium and aluminium alloys matrix composites and titanium alloy matrix composite on the basis of the X-ray absorption coefficients of the included elements in composites, respectively. The inner fibers and debonding parts of the interface between fiber and matrix were clearly found for SiC/Al composite. In the case of SiC/Al and SiC/A6061 aluminium composite the core carbon fibers of 30 μm in diameter were also observed. It is considered that the resolution of X-ray CT scanner used in this study was about 10 μm. The 3-dimensional images were reconstructed from several cross sectional CT images. It is point out that the 3-dimensional images visually displayed inner structures are very useful to examine the fracture process of the fibers contained in the metal matrix composite.

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