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

Tetsu-to-Hagané Vol. 87 (2001), No. 6

  • The Effect of Gangue Composition on the Behavior of the Fe3C Synthesis

    pp. 427-432

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    The purpose of this investigation is to clarify the effect of gangue composition (Al2O3, CaO, SiO2 and MgO) in the hematite pellets on the synthesis of Fe3C pellets. Pure hematite pellets and those contained one, two or three kinds of the gangue compositions were reacted in the atmosphere with H2-30vol%CH4gas mixture at 750°C.
    It was confirmed that the Fe3C were produced when the pellets containing Al2O3 (1, 3, 5 mass%), MgO (1, 3, 5 mass%) and SiO2 (5 mass%) were reduced. All of the reduced pellets had the similar supecific surface area. However, the structure of reduced iron phase were different form each other. The reduced pellets containing Fe3C had the iron phase with many micro pores, and the reduced pellets containing no Fe3C had that with no micro pores.
    For the pellets contained two or three kinds of the gangue compositions, it was recognized that the formation of Fe3C is suppressed by CaO and promoted by Al2O3.
  • "In-situ" Observation of Phase Transformation and MnS Precipitation in Fe-Si Alloys

    pp. 433-440

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    "In-situ" observation of MnS precipitation in Fe-Si alloys was made on cooling using a confocal scanning laser microscope. The phase transformation during cooling in low Si alloys (less than 2.0 mass% Si) was from δ phase via γ phase to α phase, but that in high Si alloys (more than 3.0 mass% Si) was from δ phase to δ+γ phase. The MnS precipitation in low Si alloys occurred in two steps but in high Si alloys in one step. In low Si alloys some large MnS precipitates appeared in high temperature by the solute pile up, and many small MnS precipitates appeared in low temperature by the change of the solubility due to phase transformation. In high Si alloys, in which δ phase and γ phase were present at the same time, most MnS precipitate in δ phase according to the high supersaturation of Mn and S in comparison with γ phase. The precipitates in δ phase grew fast, but those in γ phase grew very slowly, since the diffusion coefficients of Mn and S in γ phase are much smaller than those in δ phase.
  • Nonlinear Phenomena of Spectral Emissivity during the Steel-oxidizing

    pp. 441-448

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    The authors have made clear that spectral emissivity ε(λ0, t) of non-oxidized steel at the effective wavelength (λ0=0.65 μm) of optical pyrometer is approximately 0.4 and that the wavelength dependency in visible region is negative. But in case of oxidized surface, above-mentioned ε(λ0, t) is increased to approximately 0.9 and the wavelength dependency is changed from negative to positive.
    When the oxidized film thickness is increasing, it is known that ε(λ0, t) does not increase monotonously but increase in vibratory curve.
    The above-mentioned process is not still made clear yet.
    In this paper, the spectral emissivity ε(λ0, t) and the ratio of emissivity ε(λ1, t)/ε(λ2, t) at the two effective wavelengths (λ1, λ2) of twocolor pyrometer are measured during the steel oxidizing. And the vibratory curve should be considered as the light interference phenomenon.
    Consequently, taking account of nonlinearity, the dispersion model of light interference phenomenon is proposed and the experimental results can be explained well by the model.
  • Sensitive Determination of Antimony in Steels by High Power Nitrogen Microwave Induced Plasma Atomic Emission Spectrometry Coupled with Hydride Generation Technique

    pp. 449-453

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    The feasibility of an annular-shaped high power nitrogen microwave induced plasma (N2-MIP) atomic emission spectrometry (AES) has been studied for the determination of antimony in combination with hydride evolution method. Under the optimized experimental conditions, the best attainable detection limits at Sb I 231.147 nm line by use of N2-MIP-AES coupled with hydride generation technique was 1.87 ng Sb/ml with a linear dynamic range of 5 to 10, 000 ng Sb/ml. The presence of several diverse elements was found to cause more or less a depressing interference with the determination of antimony by the present technique. Of the several pre-reductants examined, L-cysteine was found to be the most preferable to reduce Sb5+ to Sb3+ prior to hydride generation. Therefore, L-cysteine was utilized as a pre-reductant for the determination of total antimony, i.e., Sb3++Sb5+. When antimony in steels was determined, a large amount of Fe3+ in the solution caused a severe depressing interference with the antimony determination, while the presence of Fe2+ showed little or no significant interference. Of the several interference-releasing agents examined, L-cysteine was found to be the most preferable to reduce Fe3+ to Fe2+. The proposed method using L-cysteine not only as a pre-reductant but also as an interference-releasing agent was applied to the determination of low concentrations of antimony in carbon steels. The results obtained by this method were in good agreement with the certified values.
  • Effect of Heating Rate on Structural Changes of Heat-treated Coals

    pp. 454-458

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    For high-caking Goonyella and low-caking Witbank coals, dynamic viscoelasticity was measured at heating rates of 3-80°C/min. An increase in heating rate shifted the temperature which gives the maximum fusibility to higher temperature. Structural analyses (solvent extraction, ultimate analysis and FT-IR measurement) for the heat-treated coals showed that the temperature which the extraction yields, H/C atomic ratio and aromaticity greatly change also shifted to higher temperature by increasing heating rate, while (O+S)/C atomic ratio was not influenced by the heating rate so much. The enhanced fusibility by an increase in heating rate can be the result of decrease in possibility of cross-linking related to oxygen and sulfur functionalities.
  • Development of an Electrolytic Descaling Process for Titanium Plates

    pp. 459-466

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    A new descaling process for cold rolled and annealed titanium metal strip was developed in order to produce defectfree titanium plates efficiently. The process includes newly introduced electrolysis in certain electrolytes which promotes the descaling in cooperation with the preceding salt bath treatment (immersion in fused alkali-salt mixture) and the following pickling with nitric-hydrofluoric acid. Laboratory study by anodic electrolysis showed that HNO3 or HNO3-NaNO3 solution was most effective electrolyte for promoting descaling, and NaOH-NaNO3, HNO3-H2SO4 or Na2SO4-NaNO3 solution was also effective more or less, but H2SO4, HCl or NaOH solution was scarecely effective. It was also confirmed that intermittent alternate current electrolysis in HNO3 solution promoted descaling without absorbing hydrogen and the current density on the electrolysis was desirable to be 15-20 A/dm2. Chemical analysis of the electrolyte by ICP emission spectroscopy and surface analysis of the specimen by GDS proved that the titanium scale dissolved by the anodic electrolysis, and current measurement on the electrolysis suggested that the dissolution was made easy by the salt bath treatment. Finally, the effectiveness of the electrolysis was verified by a manufacturing test using titanium metal strip.

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