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

Tetsu-to-Hagané Vol. 101 (2015), No. 10

  • Basic Examination of Briquetting Technology for Ferro-coke Process on 0.5 t/d Bench Scale Plant

    pp. 515-523

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    DOI:10.2355/tetsutohagane.TETSU-2015-038

    In recent years, the development of innovative energy saving technologies for preventing global warming has become necessary. Means of realizing innovative energy saving in the steel industry and radical low reduction agent ratio (RAR) operation in the blast furnace include improvement of the heat balance and active control of the reduction equilibrium (temperature of thermal reserve zone).
    The ‘R&D and preparatory research work for the blast furnace based innovative ironmaking technologies’ was actively promoted by the New Energy and industrial Technology Development Organization (NEDO) in November 2006 for usage of low graded raw materials and CO2 mitigation in ironmaking process. The production processes and reaction mechanisms in a blast furnace were studied for an innovative raw material -Ferro-coke- for satisfying both high coke reactivity and iron ore reduction, focusing on the temperature of the thermal reserve zone.
    Ferro-coke produced by mixing coal and iron ore (pellet feed) and densification by briquetting, followed by carbonization of the briquetted materials. The results of a fundamental investigation of the production process for ferro-coke as a new blast furnace burden material obtained by carbonization of the densified briquettes clarified the following:
    (1) The adhesion ratio of each briquette was measured for the mix of slightly caking coal and a non-caking coal at a lab-scale carbonization furnace. The adhesion of each briquette strongly depends on coal type and the blending condition for each coal. The adhesion was prevented by addition of the non-caking coal.
    (2) In the ferro-coke production, two conventional binders are used, coal-tar pitch from coke oven, SOP, and pitch from petro-chemical industry, asphalt pitch, ASP, to improve green briquette and ferro-coke strength. The synergistic effect of ASP and SOP can be regarded as a shift of low molecular weight components of ASP to SOP.
    (3) The bench scale plant of a production capacity 0.5 t/d was designed to realize the heating pattern by means of an electric heater. Continuous experiments for more than 48hours have been confirmed the ferro-coke process reliability at a bench scale plant.
  • Fundamental Investigation of High-temperature Reduction and Melting Behavior of Manganese Ore

    pp. 524-529

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    DOI:10.2355/tetsutohagane.TETSU-2015-030

    Several studies have examined the reduction behavior of manganese ore at high temperature with the aim of reducing the manganese cost in the steelmaking process. However, the transformation behavior of manganese compounds at high temperatures had not yet been clarified. Therefore, in this paper, the effects of temperature and oxygen partial pressure, as well as chemical composition, on the transformation and melting behavior of manganese ore were investigated using high-temperature X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA) in order to obtain fundamental information on the pre-reduction process of manganese ore. The main manganese compound in the raw manganese ore used in this study was characterized as CaMn6SiO12 by XRD at room temperature, while the main manganese compounds in the sintered manganese ore were Mn3O4 and MnO. Under a vacuum condition, raw manganese ore and sintered manganese ore were reduced to MnO above 1473 K. However, under atmospheric conditions (pressure: 760 Torr), manganese ore was reduced to Mn3O4 rather than MnO at temperatures above 1073 K. The results of high-temperature XRD agreed with thermodynamic calculations. The melting point of the raw manganese ore evaluated by TG-DTA was lower than that of the sintered manganese ore due to the difference in the manganese oxide in each ore rather than the difference in the content of gangue components such as Al2O3, CaO, MgO and Fe2O3. The higher melting temperature of the sintered manganese ore is interpreted in terms of a higher content of MnO due to heat treatment.
  • Effect of Lattice Defects on Tribological Behavior for Low Friction Coefficient under Lubricant in Nanostructured Steels

    pp. 530-535

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    DOI:10.2355/tetsutohagane.TETSU-2015-034

    The effect of lattice defects on the tribological behavior for low friction coefficient under lubricant was investigated in the nanostructured steels produced by heavy plastic deformation processes. In the surface-nanostructured SUJ2 bearing steel, the stable tribological behavior with low friction coefficient was observed in the ball-on-disk tests under PAO (Poly-α-Olefin 17) - oil or ester - oil, in comparison with the non-deformed steel. This phenomenon was enhanced by using the lubricant with polarity (ester - oil). In addition, the similar phenomenon was observed in the ULC (ultra-low carbon) steel with high-density of lattice defects (grain boundary, dislocation and so on). This reason seems that the molecules of lubricant interacted strongly with the nanostructured surface due to the deviation of electrons (polarization) at the region with high-density of lattice defects.
  • Onset of Secondary Recrystallization in High Purity 3.3%Si Steel

    pp. 536-545

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    DOI:10.2355/tetsutohagane.TETSU-2015-028

    Possibility of the occurrence of secondary recrystallization in high purity material without containing inhibitor elements was investigated experimentally. Only in the sample with primary recrystallization annealing performed at 900°C, onset of secondary recrystallization was observed. The orientation of secondary recrystallized grains proved to be {110} <001> (Goss) orientation. It was also shown that normal grain growth was suppressed in the sample in which secondary recrystallization occurred. Narrow grain size distribution and strong texture accumulation were considered to help the stabilization of the matrix grains.
    Texture development during secondary recrystallization in the absence of inhibitors was discussed based on proposed growth models. It was shown from Grain Boundary Character Distribution (GBCD) analysis that the High Energy (HE) boundary model was applicable to secondary recrystallization and the Solid State Wetting (SSW) model was applicable to normal grain growth. The HE boundary was related theoretically to high mobility through high grain boundary diffusion coefficient. It was considered that reducing impurity elements exerted inherent high mobility of the HE boundary and hence led to the onset of the secondary recrystallization.
  • Suppression Mechanism of Strain-age Hardening in Carbon Steel Associated with Hydrogen Uptake

    pp. 546-551

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    DOI:10.2355/tetsutohagane.TETSU-2015-033

    We investigated the suppression mechanism of strain-age hardening in a ferritic carbon steel associated with hydrogen uptake. We considered hydrogen-related three factors suppressing the strain aging: 1) solution softening, for instance, arising from a reduction in Peierls potential of screw dislocations and a change in Young’s modulus, 2) suppression of dislocation-carbon interaction through hydrogen/carbon site competition, and 3) change in plastic strain evolution behavior by hydrogen-enhanced localized plasticity (HELP). According to the present experiments under in-situ hydrogen charging, it was concluded that the solution softening (factor1) and the site competition (factor2) by hydrogen did not significantly suppress the strain aging but the change in the pre-straining behavior (factor3) did.
  • Notch Sensitivity in Fatigue Limit of High Strength Steel

    pp. 552-558

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    DOI:10.2355/tetsutohagane.TETSU-2015-045

    The fatigue limit of a tempered martensitic steel was evaluated in specimens with stress concentration sources, which were introduced with a small drill and focused ion beam (FIB). In a previous study using ferrite-pearlite steel, the fatigue limit of a specimen with a FIB notch was almost the same as the fatigue limit of a specimen with a drill hole, and the non-propagating cracks were found around both shapes of stress concentration sources. However, the fatigue limit of the specimen with a FIB notch was about 100 MPa lower than the fatigue limit of the specimen with a drill hole in tempered martensitic steel. Additionally, the non-propagating crack was observed only in the specimen with a FIB notch. The stress concentration source shapes in both materials are the same, then the difference in fatigue limit stems from the material property. This indicates that there is applicable range where stress concentration source is regarded as a pre-crack, and the range depends on material. At first, the reason for the difference in fatigue limit was discussed in terms of the non-propagating crack. In this part, we discussed non-propagating crack phenomenon around drill hole. Secondly, the effect of hardness which caused the difference in fatigue limit was discussed by using an analytical result of Dugdale model. Finally, we inferred the notch sensitivity from the propagation by deformation at crack tip. After that, we concluded that the propagation by fracture at crack tip is also important factor in analyzing notch sensitivity.

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