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

Tetsu-to-Hagané Vol. 98 (2012), No. 10

  • Enhancement of Low-temperature Gasification and Reduction by Using Iron Coke in Laboratory Scale Tests

    pp. 517-525

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    DOI:10.2355/tetsutohagane.98.517

    Iron-coke having various amount of M.Fe were produced in laboratory scale and the influence of M.Fe content in Iron-coke on reaction behavior under the condition simulating blast furnace has been investigated. Cold strength of Iron-coke products was decreased with an increase of mixing ratio of iron ore mostly due to a prevention of dilatation of coal particles by iron ore, resulting in weak bonding of coal particles. Nevertheless formed Iron-coke with iron ore in the fraction up to 30 % would have enough strength for use in blast furnace as nut coke. Both CRI and JIS-reactivity were enhanced by increasing ratio of mixed iron ore, confirming the catalysis effect of M.Fe. The temperature at which carbon consumption started was lowered with an increase of T.Fe in coke. Formed Iron-coke containing 43 % of T.Fe started reaction consuming its carbon at lower temperature than conventional coke by 150 °C. Furthermore, consumed carbon ratio was improved by M.Fe installation to coke due to increasing gasification. Process evaluation with using Iron-coke in blast furnace was performed by BIS test. It was revealed that using formed Iron-coke having 43 % of T.Fe for blast furnace resulted in an increase of shaft efficiency by 6.8%. It was found that to lower the reducing agent rate in blast furnace by decreasing the temperature of thermal reserve zone, lowering the beginning temperature of coke reaction was effective. Usage of Iron-coke having M.Fe catalyst within coke matrix is one of the methods.
  • Hydrogen-induced Breakout in Continuous Casting of Non-degassed Steel

    pp. 526-533

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    DOI:10.2355/tetsutohagane.98.526

    Hydrogen-induced sticker breakouts in aluminum-killed steel production without a degassing route have often been reported elsewhere, but so far, yet the mechanism has not been thoroughly explained quantitatively. In order to obtain a better understanding of this phenomenon, hydrogen gas evolution from the solidified shell at the early stage of solidification in continuous casting was analyzed, taking into account the δ→γ transformation. It is concluded that lower hydrogen contents, lower casting speeds and higher consumption rates of mold powder are preferable to prevent the hydrogen-induced breakouts of aluminum-killed non-degassed steel.
  • Analysis of Metal Vapor Behavior in Gas Shielded Arc Welding with Consumable Electrode by Imagining Spectroscopy

    pp. 534-540

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    DOI:10.2355/tetsutohagane.98.534

    In the present research, a general-purpose method for measurement and visualization of temperature of plasma and concentration of metal vapor in gas shielded arc welding with consumable electrode is conducted. Monochromatic images by double high-speed video-cameras are utilized to obtain the dynamic temperature of plasma and the dynamic concentration of metal vapor in arcs. Whole arc plasma photographed by the high-speed video-cameras during arc welding is treated with plasma diagnostics.
    Consequently, visualizations of plasma temperature and metal vapor concentration succeed during gas shielded arc welding with consumable electrode. Metal vapor which evaporate from the tip surface of a consumable electrode is transported by the plasma jet from the consumable electrode towards the weld pool. Therefore, temperature near the arc axis where concentration of metal vapor is high decreases. This means that the dual structure consisting of a low temperature zone by metal vapor plasma near the arc axis and a high temperature zone by shielding gas plasma at surrounding of the arc.
  • Pressure-induced Phase Transformation Behavior in α-Mn Steels by High-pressure Torsion Straining

    pp. 541-547

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    DOI:10.2355/tetsutohagane.98.541

    The influences of strain and compressive stress on the α to ε phase transformation behavior in α-Mn steels were investigated by means of high-pressure torsion (HPT). In addition, the influence of Mn addition, i.e. 10, 12, 15 mass%Mn, which increases the stability of ε phase relative to α phase on it was also investigated.
    The stabilization of ε phase in the 12 and 15 mass%Mn steels at ambient condition occurred via the application of HPT-straining in the ε phase state, but no ε phase was observed in the 10 mass%Mn steel. The fraction of ε phase increased with the strain and/or the compressive stress in the HPT-straining. This dependence on them was emphasized by the addition of Mn. In the HPT-processed specimens, the Burgers orientation relationship was observed between α and ε phases. This shows that the α phase transformed completely into the ε phase by the compressive stress in the HPT-straining and then the ε phase reverse-transformed partially into the α phase after unloading the compressive stress.
  • Mechanism of Brittle Crack Arrest Toughness Improvement Due to Texture

    pp. 548-557

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    DOI:10.2355/tetsutohagane.98.548

    Fracture surface morphologies in ESSO test specimens were examined to investigate the enhancement of brittle crack arrest toughness due to texture. In the steels with high crack arrest toughness due to texture, many sub-cracks were detected on the fracture surface during fast crack propagation. The cross sectional observations of the fracture surfaces revealed that these sub-cracks on fracture surface resulted from crack-micro-branching. The mechanism of crack-micro-branching was also investigated from the viewpoint of the crystallographic orientation. FEM analyses were also conducted to examine the effect of crack-micro-branching on the stress intensity factor. The dominant effect of crack-micro-branching to reduce the fracture driving force during brittle crack propagation was discussed, comparing with the effect of macroscopic zigzag crack propagation.
  • Effect of Strain Rate on TRIP Effect in a 0.4C-1.5Si-1.2Mn Steel

    pp. 558-566

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    DOI:10.2355/tetsutohagane.98.558

    Effect of strain rate on mechanical properties and TRIP effect on TRIP-aided multi-phase steel obtained by 0.4C-1.5Si-1.2Mn steel (0.4C TRIP steel) was investigated by tensile tests with strain rates between 3.3×10−6 s−1 and 103 s−1 at room temperature. The 0.4C TRIP steel showed good uniform elongation at low strain rates below 10−3 s−1 due to TRIP effect and tensile strength increased with an increase in strain rate. The strain rate dependence on stress-induced martensitic transformation was also investigated by x-ray diffraction experiments at strain rates between 3.3×10−5 s−1 and 100 s−1. These results clearly show the stress-induced transformation should be induced momentarily by straining at the latter stage of deformation in order to obtain larger uniform elongation. By comparing the experimental results between the 0.4C TRIP and the metastable austenitic steels, it is found that the volume fraction of retained austenite and the stability of ausutenite are associated with the difference of the strain rate dependence on TRIP effect.

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