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

Tetsu-to-Hagané Vol. 85 (1999), No. 8

  • Viscosity of Ternary CaO-SiO2-Mx(F, O)y and CaO-Al2O3-Fe2O3 Melts

    pp. 571-577

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    Effects of additives (Li2O, Na2O, K2O, MgO, BaO, Al2O3, Fe2O3, TiO2, NaF, CaF2) on viscosities of CaO-SiO2 (CaO/SiO2=1) melts have been studied by a crucible-rotating method. Viscosities of CaO-Al2O3-Fe2O3 melts also have been measured.
    The addition of Al2O3 lead to increase the viscosities of CaO-SiO2 (CaO/SiO2=1) melts, and the viscosities of CaO-SiO2 (CaO/SiO2=1) melts decreased with the addition of the other elements. The viscosities of CaO-Al2O3-Fe2O3 melts of constant CaO content decreased with the substitution of Fe2O3 for Al2O3.
    Iida's equation for viscosity reproduced the experimental viscosity data for CaO-SiO2 (CaO/SiO2=1) melts except for high Al2O3 content (40 mass% Al2O3) slag.
  • Coke Degradation Mechanism in Raceway of Blast Furnace and Less Degradation Properties

    pp. 578-584

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    In order to clarify the coke degradation mechanism in the raceway of blast furnace, model experiments were conducted based on the conditions that were possible to occur in the above region by consideration of the reaction form, reaction temperature, reaction degree and impact energy with 15 kinds of coke having different strength and reactivity.
    In the above region, fine coke (-1 mm) by abrasion and small size coke (19 mm) by bulk breakage are genarated. From the coke with much small size coke generation, fine is also much generated and fine coke generation is controlled by the strength of coke at room temperature.
    Small size coke generation is controlled by micro pore volume distribution. From the coke having the following micro pore volume distribution, small size coke is little generated:
    (a) Coke with small amount of micro pore and large ratio of pore under 10 μm
    (b) Coke with large amount of micro pore and small ratio of pore under 10 μm
    CO2 gas is difficult to enter into the micro pore under 10 μm in the particle having the above micro pore volume distribution.
  • Peritectic Transformation and Austenite Grain Formation for Hyper-peritectic Carbon Steel

    pp. 585-591

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    Three binds of solidifying regions, (L+δ), (L+δ+γ) and (L+γ) have been observed in an unidirectional solidified hyper-peritectic steel sample quenched from a temperature above the solidus temperature. The primary δ phase in the (L+δ) region solidifies to a dendritic structure, and the fine columnar γ grains are exist in the boundary part of the (L+γ) region near to the (L+δ+γ). The columnar shape of the fine γ grains is caused by the shape of δ-dendrite. A transition from the fine γ grains to coarse columnar γ grains occurs in the (L+γ) region when a volume fraction of liquid lowers. The structure of coarse columnar γ grain have no relation with dendrite structure. The fine columnar γ grains disappear as a result of growth of coarse columnar γ grain. The measured temperature ranges for the (L+δ+γ) region agree with those calculated under a non-equilibrium condition. The end temperatures of peritectic reaction and solidification calculated are somewhat lower than the equilibrium temperatures, and are independent of solidification rate.
  • Tensile Strength of Chromium Steel during and after Solidification

    pp. 592-598

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    Phase dependence of tensile strength of chromium steel during and after solidification has been studied by a technique for high temperature tensile test. The experimental technique enabled a sample to melt and solidify without crucible, and we can measure a minute load in a solidification temperature range by the experimental technique.
    A numerical model for the analysis of phase transformation during and after solidification was developed with an assumption of local equilibrium at liquid/solid interface or δ/γ phase interface.
    The zero strength temperature was in agreement with zero ductility temperature, and both of them appeared at the solid fraction of about 0.8.
    The tensile strength of chromium steel was dependent on the phase state but not chromium contents. Equations for prediction of tensile strength of δ and γ phases were determined using the experimental results in combination with the previous results for carbon steel and stainless steel.
    σδ=0.014(Tδ, strat-T)+1.2, MPa
    σγ=0.067(Tγ, strat-T)+ 6.7, MPa
    Tensile strength of δ phase state is smaller than that of γ phase, and temperature dependence of tensile strength of δ phase is also smaller than that of γ phase.
    The tensile strength of δ and γ coexisting phase is predicted from the following equation.
    σ(δ+γ)δ·fδγ·fγ
    These estimated values are in good agreement with experimental results.
    x

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  • Examination of Effective Factor on Curling and Curling Control in Plate Rolling

    pp. 599-604

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    To realize a technique for the control of curling during plate rolling, the curling behavior in actual rolling was investigated by examining the real nature in an actual mill and by the deformation analysis of the plate during rolling based on rigid-plastic FEM. Main results were the following: (1) In addition to factors that has been investigated previously, the curling behavior is remarkably influenced by the asymmetry in the phase transformation and residual strain due to the asymmetrical temperature distribution in the thickness direction. (2) To control the asymmetry in these factors, it is necessary to control the asymmetrical temperature distribution in the thickness direction with a consideration of its effect upon these factors in not only rolling process, but also the preceding process of it. On the basis of the results obtained, effectiveness of a technique for controlling curling based on the control of the vertical temperature difference in the whole process, from reheating to rolling, was confirmed.
  • Mechanical Properties of Spring Wire Drawn and Tempered at Lower Bainite Region

    pp. 605-612

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    Medium carbon spring steel containing Si (SWOSC-V) was aus-drawn and temperd at 543573K (lower bainite region) to obtain the wire with ausformed bainite structure. Aus-forming refined bainitic ferrite. Especially near surface, bainitic ferrite tended to align in one direction because of a large amount of redundant shear strain in drawing. The redundant shear strain also resulted in larger hardness near the surface especially in the cases of low drawing velocities and large die-cone angles. At center regions, the aus-formed bainite wires showed smaller hardness than that of a conventional oil quenched and tempered wire with tempered martensite structure possibly due to higher transformation temperature by heat generation during drawing. The aus-formed bainite wires had large amount of retained austenite up to 25%. The retained austenite transformed to martensite during shot-peening or fatigue testing, so that the aus-formed bainite wires showed good mechanical properties and fatigue strength comparable to those of the conventional wires. These results indicate that the present new and simple process (aus-drawing+tempering) could be applicable to practical use for spring wire production.
  • Effect of Acid Solve Al, N and Normalizing Condition on Graphite Precipitation in B Added High Carbon Sheet Steel

    pp. 613-619

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    Graphitization in high carbon sheet steel, which reduces its tensile strength and increases its elongation, is expected to improve both formability and quench hardenability. However, it is examined to shorten annealing period for graphitization in recent investigation with B added steel, clear and accurate mechanism had not been obtained. In this work, the effect of Al, N and microstructure, prior to annealing, on the relationship between graphitization and annealing period was investigated.
    0.65%C-0.2%Si-0.15%Mn-0.002%B steels, with Al ranging from 0.01 to 0.10%, and N ranging from 0.0 to 0.09%were provided. These steels were varied its microstructure by normalizing at 900°C prior to cold rolling, then microscopic observation was conducted at various period of annealing at 670°C.
    Under the condition, a remarkable graphitization was brought in steel with higher Al content. On the other hand, N was found to be weekly affected to the graphitization. However, steels, normalized prior to cold rolling, graphitization during annealing was promoted, exceeded addtion of Al inhibited its graphitization. BN, which becomes of nucleus of graphite precipitation, was reduced by exceedingly added Al. Therefore, graphitization was thought to be inhibited insome condition of steels with exceedingly high Al and normalizing prior to cold rolling and annealing.
  • Ferrite Grain Size Refinement by Heavy Deformation during Accelerated Cooling in Low-carbon Steel

    pp. 620-627

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    It is well established that the ferrite grain size of low-carbon steel can be refined by hot rolling of the austenite at temperature below the nonrecrystallization temperature (Tnr). The strain retained in the austenite increases the number of ferrite nuclei. In present study a C-Mn steel is heavily deformed by compression at temperature below the determined Tnr for this steel during accelerated cooling. Compression experiments are carried out at various cooling rates before deformation and temperatures. The ferrite grain size and the ferrite/bainite phase fraction are extensively examined. It is observed that heavy deformation during accelerated cooling widens the range of transformation temperature of austenite to ferrite. If cooling rate before deformation is set to be high (50 K/s) and deformation temperature decreases down to 530°C, the attainable fraction of ferrite increases instead of decrease of bainite. Ferrite could be a predominate phase transformed from severely deformed austenite at significantly low temperature (down to 530°C), in which, unless deformed, bainite commonly forms from austenite. Enabling the transformation to ferrite at very low temperature leads to a progressive reduction of the ferrite grain size down to 1 μm. Possible mechanism of the strain assisted low temperature transformation to ferrite is discussed.
  • Doughnut-like Cementite Formed on the {110} Surface of an Fe-3%Si Single Crystal under High Temperature Carburizing

    pp. 628-632

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    High temperature carburization was done using the {110} surface of an Fe-3%Si single crystal. The carbide morphology of specimen surface was observed by the scanning and transmission electron microscopes.
    Doughnut-like cementite (Fe3C) of 50-200 nm in carburizing temperatures of 1173-1273K was formed on the {110} surface of an Fe-3%Si single crystal, and they formed with the colonies of the fine particles of about 2-5 nm. The preferential formation of Fe3C was quite different from the graphite formation that occured only under the high temperature carburization of past experiments.
    The orientation relationship between the Fe3C and iron matrix is considered to be [002]Cementite//[011]Fe. This relationship was consistent with that observed in the precipitation of Fe3C during the tempering of steel by Nishida and Tanino.
    It is considered that the {110} surface of an Fe-3%Si single crystal under the high temperature carburization formed with characteristic morphology of doughnut-like Fe3C, due to the preferential formation of the coherency for the crystallographic plane of (011)Fe and (002)Cementite.
  • Mechanism of Strong Formation of {111} Recrystallization Texture of Cold Rolled IF Steel Sheet with {111} Hot Band Texture

    pp. 633-638

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    For a new industrially processed hot rolled Ti+Nb IF steel, finished in the ferrite region with significant lubrication, the texture development during cold rolling and annealing was investigated. Imaging Microscopy (OIM) reveals that γ-fibre grains nucleate and grow in the beginning of recrystallisation by consuming γ-fibre components of the deformed matrix. The predominant nucleation of the {111}<110> grains from the {111}<112> matrix can be understood by assuming <112> rotation, which corresponds to the occurrence of the {110}<111> slip system. Such the slip behaviour and the texture evolution mechanism, originally proposed by the present authors, group in a single crystalline 3% Si steel, is widely applicable to the mechanism of the {111} texture development of deep drawable cold-rolled steel.

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