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

Tetsu-to-Hagané Vol. 91 (2005), No. 10

  • Investigation on the Dioxin Emission from a Commercial Sintering Plant

    pp. 745-750

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    Recent studies concerning the dioxins emission from the iron ore sintering process have clarified a dominant mechanism of dioxins formation and the substances to promote or to inhibit the reaction. In this paper, a detailed analysis of the exhaust gas in Oita No.1 sintering plant has specified the strand positions where dioxins were released to the exhaust gas. The release of dioxins was detected at two different positions. The first release position was located at the point where the drying zone reached to the hearth layer, showing a broad peek containing a large amount of furans. The second release position was located at the point where the melting zone reached to the heath layer, showing a sharp peek. Differences in dioxins congeners at the release positions imply different mechanism of dioxins formation. The dioxins of the second release are considered to be formed in wind boxes at temperatures of 300°C or more. Controlling the burn through point to the discharge end is supposed to be effective for decreasing the dioxins emission in the second step.
  • Functional Forms of Carbon and Chlorine in Dust Samples Formed in the Sintering Process of Iron Ores

    pp. 751-756

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    The chemical forms of the carbon and chlorine present in dust samples obtained from windboxes of the iron are sintering machine have been studied with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The chlorine in the dust samples is present as KCl with the average crystalline size of 40-50 nm and covalent C-Cl bonds in condensed aromatic structures of unburned carbon surface. The proportion of chlorinated aromatic structures increases almost linearly with increasing that of surface oxygen complexes on unburned carbon, strongly suggesting that active surface sites of the carbon formed in the sintering process work as reaction sites with HCl and Cl2. Model experiments using a coke show that HCl reacts with it at 500°C to form several types of Cl-functional forms, from which the HCl desorption takes place at the wide range of 500-900°C upon reheating. Such a profile for HCl formation is almost unchanged after washing of the HCl-treated coke by water. These observations indicate the formation of organic chlorides. It is therefore likely that HCl and Cl2 evolved in the combustion process react with active sites of unburned carbon surface to form organic chlorine compounds.
  • Analysis of Visibility of Exhaust Gas in the Iron Ore Sintering Plant

    pp. 757-762

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    Visible smokes of exhaust gas from the iron ore sintering plant give an unfavorable impression on scenery around the Works. In this paper, a mechanism of formation of visible smoke was discussed by detailed analysis of the exhaust gas components and dusts in Oita No. 1 sintering plant. Main substance of visible smoke was mist condensing in the air during cooling of exhaust gas that contains 0.1ppm of sulfuric acid(SO3). Sulfuric acid is considered to raise the dew point that mist condensation became easier and to lower the vaporization of visible mist consist of sulfuric acid solution. Dusts in the exhaust gas are also considered to play a role of the nuclear of mist condensation. This proposed mechanism was confirmed by the test remixing SOx rich gas with desulfurization gas in Nagoya No. 3 sintering plant. Long visible smoke was observed by remixing SOx rich gas with exhaust gas. As a conclusion, enhancement of dust collecting system is not enough to accomplish invisible exhaust gas. Desulfurization equipment is necessary for invisible exhaust gas in the sintering plant.
  • Development of Optimum Argon Shrouding System between Ladle and Tundish

    pp. 763-768

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    Experimental investigation has been carried out using three kinds of pouring tubes to establish an optimal Ar gas seal technology for the continuous casting tundish. The following findings are obtained.
    (1) The Ar gas seal effect in the pouring tube is dependent on the Ar gas flow rate and the distance between the Ar gas blow position and molten steel surface.
    (2) The performance of the seal of the pouring tube during ladle exchange is evaluated by the pressure of nitrogen, PN2.
    (3) When newly developed pouring tube of type-C is used in place of the conventional tube of Type-A, the number of inclusions in the slab, of which diameters are equal to or more than 120μm, is reduced by about 50% at the steady parts and by about 40% at the ladle exchange parts.
    (4) The deposit thickness on the tube wall of Type-C decreases to 1/3 of the thickness for Type-A. Accordingly, the pouring tube of Type-C can be reused.
  • The Neck Growth Model in a Smooth Round Tension and a Circumferentially Notched Tension

    pp. 769-774

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    The neck growth by plastic working was investigated by circumferentially notched tension test and smooth round tension test at room temperature. The neck ratio, defined as the radius of the neck section divided by the radius of the neck curvature, changes with the true strain. The initial notch shape affects the neck growth by plastic working before local necking but it has no effect after local necking. Therefore, changes in the neck ratio with the true strain before and after local necking were expressed by different neck growth models for the circumferentially notched tension. The neck growth models on the smooth round tension and the circumferentially notched tension are in reasonable agreement with the experimental results.
  • New Hot-rolled High Carbon Steel Sheets with Excellent Stretch-flange Formability

    pp. 775-782

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    The effect of microstructure on the stretch-flangeability of JIS S35C hot-rolled steel sheets was studied from the viewpoint of the initiation/growth of voids in the hole-expanding process with ferrite-pearlite and spheroidized cementite steels.
    In a comparison of ferrite-pearlite steel and spheroidized fine-grained cementite steel, total elongation was higher with the ferrite-pearlite structure, while the hole-expanding ratio (λ) of the spheroidized cementite structure, which is an index of stretch-flangeability, was superior to that of the ferrite-pearlite structure. The hole-expanding ratio has a strong correlation with notched-tensile elongation, and a linear relationship was obtained with a long gauge length of GL=50mm.
    A notch-shaped crack occurred at the surface of the punched hole of the ferrite-pearlite steel in the hole-expanding test and rapidly propagated along the ferrite-pearlite interface in the subsequent hole-expanding process.
    In contrast, the punched hole surface of the spheroidized cementite steel was smooth, and after void initiation/growth in the hole-expanding process, voids developed into cracks by coalescence, resulting in a homogeneous distribution of work strain.
  • Effect of Steel-making Slag Addition on Growth of the Diatom Skeletonema costatum and the Dinoflagellate Alexandrium tamarense

    pp. 783-787

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    Effects of steel-making slag addition on growth of the diatom Skeletonema costatum and the dinoflagellate Alexandrium tamarense, which are common phytoplankton species in spring in Hiroshima Bay, were examined. While the growth of S. costatum was intensified optimally with addition of 100mg slag L-1, that of A. tamarense was depressed with addition of the slag in the range of 50-150mg L-1. From monitoring nutrient concentrations, it was clear that S. costatum utilized efficiently the nutrients dissolved from the slag. On the other hand, A. tamarense appeared to be too sensitive to pH increase by slag addition to grow. The different growth responses were discussed in terms of the carbonate-pH system. It is concluded that an application of steel-making slag can be a useful measure to remediate coastal marine ecosystems where Si and P are depleted if amount and timing of addition are well studied.

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