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

Tetsu-to-Hagané Vol. 81 (1995), No. 2

  • Basic Segregation Mechanism of Solids Bed and Its Reduction

    pp. 89-97

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  • Interphase Boundary Structures in Phase Transformation and Precipitation Processes

    pp. 98-104

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  • Mean Flow and Turbulence of Water in a Cylindrical Vessel Agitated by Bottom Air Injection

    pp. 105-110

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    Cold model experiments based upon aqueous systems were carried out to study the mean velocity and turbulence intensity in a cylindrical bath. The axial and radial velocity components in the cylindrical bath agitated by air injection through a centered single-hole bottom nozzle were measured using a two-dimensional laser Doppler velocimeter. The spatial mean kinetic energy for the time-averaged component km, v and that for the turbulence component kt, v were obtained. It was found that km, v and kt, v depended on 0.60 and 0.72 powers of the injected gas flow rate, respectively. The energy supplied by the injected gas into the bath therefore was more consumed to maintain turbulent motions than to do the mean flow, i.e., the circulating flow as the gas flow rate increased. Measured values of the spatial mean velocity Vm, v=(2km, v)1/2 were satisfactorily approximated by an empirical correlation proposed so far, but the dependence of the present Vm, v values on the bath depth Hw and bath diameter D was different from this correlation. The spatial mean turbulence intensity Tuv=(kt, v/km, v)1/2 was above unity under the present experimental conditions.
  • Heat Transfer Analysis of a Single Cylinder and a Packed Bed of Carbonaceous Material in a High-Frequency Induction Furnace

    pp. 111-116

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    This paper presented experimental and theoretical study on heat transfer in a high-frequency induction furnace for scrap melting. Single cylinder located on the central axis and a packed bed of carbonaceous materials were heated to assess influence of kind and size of the samples, and induction current on both heating rate and distribution of temperature. A mathematical model based on electromagnetic theory was developed for predicting temperature, current density and electromagnetic fields, and was experimentally validated. The model included multi-layered thermal insulator as a computational area.
    During induction heating, a single graphite cylinder was heated uniformly, while a single coke cylinder showed significant temperature gradient and minimum temperature at the center. Larger size, smaller electric resistivity and larger induction current enhanced the heating rate of the cylinder. Distribution of current density was almost concentric, and current gradient was more steep in a graphite than in a coke. A packed bed of spherical graphite was heated up to the melting point of scrap under 2.95kHz and 1330A. The temperature difference within the packed bed was less than 100K with the maximum temperature at the center point.
  • Effect of the Compositions of Oxides on the Reaction between Oxide and Sulphur during Solidification of Steel

    pp. 117-122

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    In order to elucidate the reaction between oxides and sulphur in molten steel during solidification, the effect of composition of oxides in continuously cast steels has been observed and analyzed. The results obtained are as follows.
    CaO-SiO2-Al2O3 and CaO-SiO2 oxides are observed in low Al content steel (Al=0.005mass%) and CaO-Al2O3 oxides are observed in high Al content steel (Al=0.031mass%). CaO-SiO2-Al2O3 and CaO-Al2O3 oxides have higher S content than CaO-SiO2 oxides. High S content in oxides was obtained with high liquid fraction and high sulphide capacity of oxides at the solidification temperature of the steel.
    Because desulphurization by oxides which have high sulphide capacity and high liquid fraction occurs during solidification, S segregated in the center of slab is absorbed by the oxides.
  • Model Experiments with Hollow Test Pieces on Deformation of a Continuously Cast Strand under Solidification

    pp. 123-128

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    The deformation behavior of a continuously cast strand under solidification is complicated because of the interaction among wide faces, narrow faces and edges of hollow box structure. Although several theoretical analyses were reported until now, deformation behavior has remained unclarified on the whole, because the above interaction effect was not taken into account in these analyses. In this paper the deformation behavior of a continuously cast strand under solidification is investigated through a simulation experiment with hollow rubber test pieces. The following results were obtained, which enable us to estimate accurate strain in a strand to design a continuous casting machine.
    1) Unbending strain in a hollow piece varies considerably in a transverse direction, and the concept of shear lag accounts for that fact.
    2) Bulging strain at a location apart from edges conforms to the elastic beam theory, while the bulging coefficient increases with decreasing shell thickness.
    3) The existance of new type strain named winding round strain which occurs in an unbending region even without pressure is made certain and analysed quantitatively.
    4) Additivity among different kinds of strains is ascertained. Because of phase difference between different kinds of strains, knowledge of continuous strain distribution is indispensable to estimate a crack occurrence.
  • Effect of Scratch on a Substrate on a Protrusive Surface Defects of Galvannealed Steel Sheet

    pp. 129-134

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    The mechanism by which scratch leads to protrusive surface defect was investigated by observing a scratched concavity artificially created on a steel substrate, during the galvanizing and galvannealing processes. As a result of galvanizing, the concavity was reduced because the scratch was filled up with molten zinc. After galvannealing, however, a protrusive surface defect appeared on the sheet, higher than the original scratch. Moreover, during galvanizing, the alloy layer formed faster over the concavity than over the unscratched area. During galvannealing, the alloy layer over the concavity grew even more because it reacted with the molten zinc over the unscratched area. It was therefore concluded that the presence of more Zn-Fe alloy leads to increased development of protrusive surface defect.
  • Characteristics of Gas Wiping Jet in Hot-Dip Coating Process

    pp. 135-140

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    As for the characteristics of the gas wiping jet in the hot-dip coating process, the flow coefficient, the velocity profile and the impinging wall pressure distribution of a plane jet are investigated using two types of model nozzle.
    The friction loss of the wiping nozzle is 1% or less when the ratio of lip length to slit gap is not more than 5. The inner shape of the wiping nozzle has no effect on the characteristics of the wiping jet. The impinging wall pressure at the plate edge is low and the wall pressure distribution is gently as compared with those at the plate center. It is considered that this is the probable cause of edge over coatings. The velocity distribution of the impinging wall jet agrees with Verhoff equation for the wall jet injected parallel to a wall. The velocity scale of the impinging wall jet is affected by the nozzle slit gap and the wiping angle, but the length scale is independent of those values.
  • Strain Measurement by Intra-granular Distortion Analysis in Creep of 2.25Cr-1Mo Steel

    pp. 141-146

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    Intra-granular creep distortion of 2.25Cr-1Mo steel deformed at 843K and 106MPa has been investigated by transmission electron microscopy (TEM). Intra-granular distortion detected by Kikuchi pattern shifting was observed quite early (<1% strain) before sub-grain structure is developed. Average misorientation change was proportional to the distance between measurement points in the grain. In order to determine average internal distortion ed, mean values of tilt angle/distance from certain point were calculated in several grains. Internal distortion ed showed good correlation with creep strain ec under the test condition and preparaed a method of creep strain measurement.
  • Austenite Grain Size Control by Insoluble Carbide in Martensitic Stainless Steels

    pp. 147-152

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    Effect of insoluble carbide on the size of prior austenite (γ) grains was investigated in martensitic stainless steels with the chemical composition of 12%Cr-(0.120.34)%C(in mass%). When fully tempered martensite (α') is subjected to partial solution treatment ; the solution treatment in (γ+M23C6carbide) two phase region, the growth of γ grains is effectively suppressed by insoluble carbide particles retained in the γ matrix owing to the grain boundary pinning effect. The mean diameter (D) of γ grains changes depending on the volume fraction (f) and diameter (d) of dispersed carbide particles and is given by the equation ; D=β(d/f) (β=1.01.5). With increasing carbon content of steels, the growth of γ grains is suppressed up to higher temperature. For instance, γ grain size of a 12%Cr-0.34%C steel can be kept as small as about 20 μm even at a high temperature around 1300K. Smaller the size of dispersed carbide particles is, γ grain size is expected to become finer. However, the grain refining by partial solution treatment was limited to around 12μm, because, in tempered martensitic steels, homogeneous dispersion of carbide particles is not obtained due to the fact that carbide precipitates preferentially on the boundaries of martensite laths and blocks.
  • Initial aging Phenomenon before the Precipitation of Laves Phase in Fe-10%Cr Alloys

    pp. 153-155

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  • 住友金属 鹿島製鉄所 第2冷間圧延設備について

    pp. N66-N69

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