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

Tetsu-to-Hagané Vol. 87 (2001), No. 9

  • Particle Image Velocimetry (PIV) Measurement of Flow Establishment Time in a Bath Agitated by Plunging Jet

    pp. 571-578

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    The instantaneous velocity of flow in a water bath agitated by a plunging water jet was measured with particle image velocimetry (PIV). The water in the bath was initially at rest and then driven by the plunging water jet. The period from the start of plunging to the moment at which the flow in the bath becomes a steady state is defined as flow establishment time. The turbulence components were used to determine the flow establishment time in place of the commonly used mean velocity components. An empirical equation was proposed for the flow establishment time.
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  • Propagation Characteristics of Surface Wave on Free Surface of a Molten Metal Induced by Imposition of Intermittent Alternating Magnetic Field

    pp. 579-584

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    In order to increase an interfacial area for the promotion of mass transfer in refining processes, a new method exciting surface wave on a molten metal has been proposed in the way introducing an intermittent alternating magnetic field with the stepwise change of amplitude. For investigating characteristics of the induced surface waves, their behavior on a liquid gallium was measured by use of a laser level sensor and a high speed camera by changing values of a magnetic field and an intermittent frequency. Increase in the amplitude of the magnetic field provided a liquid metal disturbance, which propagated on the liquid metal surface to a center of a vessel with a constant velocity, in the vicinity of a wall. Although, propagating velocity of the surface wave slightly increased at a center of a vessel. Propagating velocity of the surface wave increased with increasing in the magnetic field and was independent of the intermittent frequency. Both the width and the height of the surface wave increased during its propagation from the wall to the center so as to keep the constant wave volume. Increase in the magnetic field changed the height and the volume of the wave while the wave width was kept constant. Increase in propagating velocity of the surface wave might be caused by increase in the height of surface wave. A part of characteristics of surface wave could be explained by Stokes wave theory.
  • Reduction, Carburization and Melting Behavior of Iron Ore Pellets containing Coal Char or Graphite on Heating

    pp. 585-592

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    Reactions in iron ore-coal char composite pellets heated in nitrogen atmosphere at temperatures between 1100°C and 1350°C were investigated. Coarsening and melting of reduced iron particles through their carburization were furthermore investigated for iron ore-coal char (pellet Pc, i) and iron ore-graphite (pellet Pg, i) composite pellets. Direct carburizaiton of iron in contact with carbon is superior to indirect carburization through gas phase. Melting of Pc, i started above 1350°C while melting of Pg, i above 1200°C. The mechanism of formation of core and shell, which were observed for both kinds of the pellets by heating for a certain time, was also discussed. Furthermore, heating experiments with electrolytic iron-coal char (pellet Pc, e) and electrolytic iron-graphite (pellet Pg, e) composite pellets in N2 and CO-10%CO2 were conducted to study the effect of gasification of carbon on melting of the iron. It is concluded that the gasification of carbon has a strong effect on the carburization by direct contact mechanism between iron and carbon, which finally determines the melting starting temperature of reduced iron.
  • Development of Diagnosis System for Roll Alignment and Roll Rotation in Continuous Casting Process

    pp. 593-599

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    A new roll alignment checker and a new roll rotation checker, which make it possible to diagnose condition of roll alignment and roll rotation at second cooling water zone in a continuous casting machine, are developed. This diagnosis system has the advantage of high accurate measurement, durability in difficult surroundings, ease of operation and lack of influence of casting time during measurement.
    Developed roll alignment checkers and roll rotation checkers are applied to continuous casting machines for slab products. Measurement repeatability, durability of on-line use over a long period and comparison between actual condition of rolls and judgement by using this method are evaluated. As a result, good repeatability of measured data, good durability of on-line use over a long period and good correspondences with actual condition of rolls are verified.
    Developed roll alignment checkers and roll rotation checkers will be utilized in continuous casting machines of the steel works, and are expected to contribute to stable operation and casting products with good quality.
  • Effect of Addition of a Very Small Amount of Carbon on the Transformation Texture of 1%Mn-0.034%Ti Extra-low Carbon Steel Sheets

    pp. 600-606

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    The development of the steel sheet, which has good combination of excellent press-formability and high strength, is achieved by the transformation structure strengthening of extra-low carbon steel sheets. The samples used are 1%Mn-0.035%Ti extra-low carbon steel cold-rolled sheets, which contain no Nb. The sheets are recrystallized and then carburized up to 189 ppm, in order to examine the effects of carbon content and heating temperature on the transformation behavior and transformation texture. (1) The transformation structure formed by quenching from γ region into iced water gives 150 HV for 16 ppm carbon and 180 HV for 49 ppmC. Moreover, the transformation structure was the quasi-polygonal ferrite and/or intermediate ferritic phase having high dislocation density, and the (111) orientation (texture) developed, which suggest the possibility of an excellent combination of high strength and good deep-drawability. (2) The formation of the lath martensite in the steel containing 189 ppm carbon promoted the development of (100) and/or (110) orientation and the decrease of (111) orientation. (3) The subboundary of intermediate transformation phase is composed of mainly incoherent interface. The relationship between the development of (111) transformation texture and the nature of interface is very stimulating and must be examined to clarify the mechanism of development of (111) texture with respect to transformation mechanism reconstructive or displacive.
  • Effect of Carbon Content on Deep Drawability of TRIP-aided Dual-phase Sheet Steels

    pp. 607-612

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    Effect of retained austenite on the deep drawing in high strength TRIP-aided dual-phase (TDP) sheet steels with different carbon content were investigated. The deep drawability based on the limiting drawing ratio (LDR=D0/dp), where the D0 and the dp are a maximum blank diameter and a punch diameter respectively, was affected by the volume fraction of the retained austenite and by its stability (carbon concentration). Namely, the higher the volume fraction of the retained austenite and its stability, the larger strength-deep drawability balance, i.e., the product of tensile strength and LDR. Furthermore, the higher blank folding force, the larger the strength-deep drawability balance of high carbon TDP steel. The excellent deep drawability was due to large local necking resistance at the cup wall just above the punch bottom due to "the transformation hardening" and "the stress relaxation" resulting from the strain-induced martensite transformation, as well as a low drawing resistance of the shrinking flange.
  • Isothermal Transformation Behavior in 12%Cr-0.3%C Steel with Partial Solution Treatment

    pp. 613-618

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    12mass%Cr-0.3mass%C steel was subjected to partial solution (PS) treatment in the two-phase region of austenite (γ)+M23C6 carbide, and then isothermally transformed to ferrite (α)+carbide at around 1000K. The isothermal decomposition behavior of γ has been investigated by means of hardness testing and microstructural observation. Time-Temperature-Transformation diagram obtained by hardness testing showed that the decomposition of γ starts much faster in the PS-treated specimens than the specimens which have been subjected to the full solution treatment in the γ single phase region, because a lot of insoluble carbide particles dispersed within γ grains provide the precipitation sites for the carbide in the subsequent isothermal decomposition treatment. Upon the decomposition of γ in the PS-treated specimens, carbide precipitates on the insoluble carbide in the made of "in-situ" type, and α nucleates simultaneously at the carbon depleted γ region adjacent to the carbide particles by the eutoctoid transformation mechanism. In this transformation, insoluble carbide particles always work as precipitation sites for carbide, hence, typical lamellar structure is not formed but equiaxed α structure is formed around spherical carbide particles which have previously dispersed in the γ matrix at a PS-treatment temperature.
  • Strain Rate Dependency of Strength in TiB Particle Reinforced Ti Matrix Composite

    pp. 619-622

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    In this study, TiB particle reinforced Ti matrix composite has been produced using a relatively new powder metallurgy process, the spark plasma sintering and its tensile properties have been investigated over a wide strain rate range. It has been clarified that tensile strength increases moderately with an increase in the strain rate below ε_??_103 s-1, and subsequently increases rapidly above it. This tendency is interpreted in terms of the Eshelby equivalent inclusion method.
    The analytical results have suggested that the strain rate dependency of strength is simply attributable to that of unreinforced matrix and no extra effects due to the addition of TiB particles are observed. The analysis also reveals that the lower bound estimate of the strength of the TiB particle is several thousand MPa which exceeds that of SiC particle reported in earlier studies. It can be concluded that the TiB particle is excellent in its in-situ strength and interfacial compatibility with the Ti matrix.
  • Separation of Iron(III) by Di(2-ethylhexyl)phosphate/4-Methyl-2-pentanone Extraction

    pp. 623-625

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