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

Tetsu-to-Hagané Vol. 96 (2010), No. 9

  • Oxidation Removal of Cu from Carbon Saturated Iron via Ag Phase

    pp. 531-535

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    DOI:10.2355/tetsutohagane.96.531

    The oxidation removal of Cu from carbon saturated iron via Ag phase was tried at 1523K. In addition, the thermodynamic data, which are necessary to know lowering limit of Cu content of carbon saturated iron by this method, are measured. The distribution ratio between carbon saturated iron and silver, LCu(mass%)(=[mass%Cu](in Ag)/[mass%Cu](in Fe–C)) and the activity coefficient of Cu in carbon saturated iron, γ°Cu(in Fe–C), are determined to be 7.15 and 50.2 at 1523K, respectively. By using these values, the lowering limit of Cu content of carbon saturated iron is calculated to be 0.21 mass% in oxygen atmosphere (1 atm) at 1523K under the condition that the activity of CuOx equals to be unity. As the experimental results of Cu oxidation removal from carbon saturated iron via Ag phase, the Cu content of carbon saturated iron is actually reduced to 0.3–0.6 from 4 mass%, and it is found that the copper in molten iron can be removed by the method proposed in the present study.
  • The Effect of Variation of the Coke Microstructure with Addition of Iron Ore on the Tensile Strength of Ferrous Coke

    pp. 536-544

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    DOI:10.2355/tetsutohagane.96.536

    The effect of variation of the coke microstructure with the addition of iron ore on the tensile strength of ferrous coke was investigated. To make ferrous coke, pressed mixture of Donaldson slightly coking coal, Copabella semi-anthracite coal and MBR iron ore were used. The tensile strength and elastic modulus of the ferrous coke were measured by diametral-compression test. Moreover, the homogenized elastic modulus was estimated by homogenization method using the cross sectional digital images of the ferrous coke. Both of the experimental and analytical results were compared, and the image analyses for the digital images were used to quantify the micro-properties and to investigate their effect on the tensile strength. The results were concluded as follows: (1) The tensile strength of the ferrous coke decreases with the addition of MBR iron ore when maximum fluidity of the raw materials is under 22 ddpm and swelling behavior does not develop, and the adhesion between coal particles is weak. (2) The tensile strength of the ferrous coke increases by variation of coke microstructure with the addition of MBR iron ore when maximum fluidity of the raw materials is greater than 22 ddpm and swelling behavior develops. It seems that the number of coarse-pores which behaves fracture origin decreases and the number of fine-pores which has minor influence on degradation of stiffness of the ferrous coke increases by the addition of MBR iron ore.
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  • Size Analysis of Nanometer Titanium Carbide in Steel by Using Small-Angle Neutron Scattering

    pp. 545-549

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    DOI:10.2355/tetsutohagane.96.545

    Utilization of nanometer size precipitates in steel is a promising technology for the developing high tensile strength steels, and it is important to analyze the size of the precipitates. Electron microscopy is a powerful method in directly determining the precipitates size, but the area observed is limited and statistical procedure is tedious. Therefore, size analysis of precipitates in steel was conducted by using small-angle neutron scattering method (SANS). Sample (0.045%C–1.8%Mn–0.2%Ti–0.004%N) with different heat treatment was used for the experiments. Size of nanometer size TiC calculated by SANS profiles agreed with that obtained by direct observation of precipitates by transmission electron microscope (TEM). We have succeeded in macroscopic and non-destructive determination of the size of nanometer-sized TiC.
  • Influence of Iron Oxide of Carbon Steel on Lubricating Properties in Seamless Pipe Hot Rolling and the Effectiveness of Borax Application

    pp. 550-556

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    DOI:10.2355/tetsutohagane.96.550

    It is empirically known that an iron oxide layer formed on a surface of work piece plays an important role of lubricating properties in hot rolling. However, very few works on the influence of iron oxide layer on lubrication properties have been reported. Therefore, we investigated the influence of thick iron oxide scale layer on lubricity in the case of carbon steel hot rolling by means of a simulation test of seamless pipe hot rolling. Furthermore, based on the result, we found the effectiveness of borax application on the surface of the work piece in terms of lubricity improvement.
    A carbon steel work piece, which has a controlled thickness of an oxide layer by heating up to the set elevated temperature followed by exposing to ambient atmosphere for the set duration, was rolled between a cylindrical roll and a flat tool lubricated with graphite-based lubricant.
    Summaries of the results are shown below.
    ① In case of high rolling reduction, the iron oxide was embedded into the substrate in rolling, which caused high friction coefficient when hard iron oxide layer generated thickly.
    ② It is effective to soften the iron oxide by, for instance, applying bolax on the work piece surface in order to prevent the iron oxide from being embedded into the substrate and from increasing the friction coefficient when the hard iron oxide scale layer generated thickly.
  • Effect of Anisotropic Yield Functions on the Accuracy of Hole Expansion Simulations for 590 MPa Grade Steel Sheet

    pp. 557-563

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    DOI:10.2355/tetsutohagane.96.557

    The deformation behavior of a high-strength steel alloy with a tensile strength of 590 MPa is investigated both experimentally and analytically to clarify the effect of the material model (anisotropic yield function) on the predictive accuracy of the finite element simulation of hole expansion. Biaxial tensile tests of the test material have been carried out. Measured contours of plastic work and the directions of plastic strain rates are found to be in good agreement with those predicted using the Yld2000-2d yield function with an exponent of 6. The anisotropy in uniaxial tensile flow stresses and r-values has been also in good agreement with those predicted by the Yld2000-2d yield function, as opposed to the previous study [T.Kuwabara, K.Hashimoto, E.Iizuka and J.-W.Yoon: J. Jpn. Soc. Technol. Plast., 50 (2009), 925]. Forming simulations of and experiments on the hole expansion of the test material have been carried out using the von Mises, Hill's quadratic and the Yld2000-2d yield functions with different exponents. The Yld2000-2d yield functions have given the closest agreement with the experimental results. Consequently, it is found that anisotropic yield functions significantly affect the predictive accuracy of the deformation behavior of an anisotropic sheet metal subjected to hole expansion and that the biaxial tensile test is effective in identifying a proper anisotropic yield function to be used in the hole expansion simulation.
  • Premature Creep Rupture and Overestimation of Rupture Life in Modified 9Cr–1Mo Steel

    pp. 564-571

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    DOI:10.2355/tetsutohagane.96.564

    Creep rupture life in the time range of 105 h and longer has been evaluated on the basis of creep rupture data available on modified 9Cr–1Mo (Gr.91) steel. The steel is strengthened by a tempered martensite lath structure, which degrades by means of strain induced recovery in short-term creep (Region H). The degradation leads to creep rupture. In long-term creep (Region L), static recovery of the martensite lath structure takes place in addition to the strain induced recovery, resulting in premature creep rupture and the consequent decrease in stress exponent n for rupture life. The premature creep rupture always occurs in Gr.91 steel, but the activation energy QL for rupture life in region L is usually close to the value QH in Region H in the steel. In such a case, long-term rupture life can be predicted correctly by simple extrapolation of short-term data. In some heats of Gr.91 steel, however, another region with low values of n and Q, namely Region L2, appears in the time range longer than 104 h. Simple extrapolation of short-term data results in overestimation of rupture life in Region L2. The static recovery and the consequent premature creep rupture are controlled by migration of sub-boundaries stabilized by precipitates. M23C6 as well as MX precipitates in Gr.91 steel have higher thermal stability than those in other high Cr ferritic steels, resulting in the later appearance or absence of Regions L and L2 in the steel.
  • Formation of New Bone with Preferentially Oriented Biological Apatite Crystals Using Novel Cylindrical Implant Containing Anisotropic Open Pores Fabricated by Electron Beam Melting (EBM) Method

    pp. 572-578

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    DOI:10.2355/tetsutohagane.96.572

    New cylindrical bone implants containing elongated pores interconnected as open pores were fabricated by an electron beam melting (EBM) method from Ti–6 mass% Al–4 mass% V ELI powders of 65 μm in mean diameter. New bone formed in the elongated pores of implant and preferential arrangement of biological apatite c-axis were confirmed along the long bone axis by the microbeam X-ray diffraction method. Bone mass and preferential degree of biological apatite c-axis as a bone quality parameter decreased with the distance from the edge of implant along the longitudinal bone axis because of a stress shielding effect. However, clear interconnection of new bone appeared through the implant with elongated pores parallel to the bone axis, while the defected portion was not recovered with new bone without the new implant.

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