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

Tetsu-to-Hagané Vol. 94 (2008), No. 9

  • Effects of Addition of Titanium and Boron on Columnar Austenite Grain in Carbon Steel

    pp. 331-335

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    DOI:10.2355/tetsutohagane.94.331

    We performed casting experiment of S45C steel, focusing on the effect of addition of Ti and B on as-cast austenite grain structure. Without the addition of these elements, the austenite structure consists of columnar grains over the whole sample in the present casting conditions. The addition of Ti and B leads to the formation of equiaxed austenite grains and, importantly, fully equiaxed austenite structure was observed in the sample with 0.2 mol% Ti and 0.4 mol % B. The microstructural observations indicated that this behavior of austenite structure stems from the columnar-to-equiaxed transition of ferrite dendrite structure. The addition of these elements, furthermore, leads to refinement of the columnar austenite grains.
  • Emission Characteristics of Laser Ablation–Hollow Cathode Helium Glow Discharge Source and the Measurement of Carbon in Steel Sample

    pp. 336-344

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    DOI:10.2355/tetsutohagane.94.336

    Emission characteristics of the laser ablation–hollow cathode helium glow discharge source were examined. It was found that one of the major excitation mechanisms of atomic emission lines having excitation energies of around 3 eV is collisions of electrons with analyte atoms, and that the collisions between sample atoms and metastable helium atoms in the glow discharge plasma play an important role in the excitation of emission lines having excitation energies larger than 4 eV. Emission peaks of atomic helium and carbon contaminants were sufficiently suppressed by the present method, i.e. simply subtracting the emission spectrum with glow discharge alone from the spectrum with both glow discharge and laser ablation. Since it is possible to distinguish between atomic emission spectrum of carbon contained in a steel sample and the spectrum of carbon contaminants in the plasma gas, the response time for the analysis of carbon will be shortened using the present method.
  • Determination of Arsenic and Antimony in “Tatara” Steel Making Sample by Neutron Activation Analysis Combined with Multiple Gamma-ray Detection

    pp. 345-350

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    DOI:10.2355/tetsutohagane.94.345

    “Tatara” is a traditional iron and steel making process in Japan. It is a kind of directly refining steel making method using a sand iron. By the authors' study, it turned out that we could estimate the source region of raw material of “Tatara” by As and Sb concentration ratio in “Tatara” sample. However, the concentration of these elements in “Tatara” sample is very low (ppm or sub-ppm order), therefore, quantitative analysis is very difficult. In this study, As and Sb in “Tatara” sample (iron lump, sand iron and slag) were determined by Neutron Activation Analysis combined with Multiple Gamma-ray detection (NAAMG). NAAMG is high sensitive and non-destructive analysis method which combined Neutron Activation Analysis (NAA) and multiple gamma-ray detectors. Each “Tatara” sample (iron lump, sand iron and slag) was irradiated for 1–2 h (for As measurement), and 8–17 h (for Sb measurement) in JRR-3M HR irradiation field (thermal neutron flux was about 9.0×1017 n m−2 s−1). After the end of irradiation, cooling time was 4–5 d (As), and 19–36 d (Sb). Coincidence gamma-rays were measured by gamma-ray detector array, GEMINI-II for 1–8 h (As), and 2–41 h (Sb). Iron and steel certified reference materials were used as comparative standards. As a result of measurement, the concentration of As and Sb in all “Tatara” samples were determined by NAAMG and these were sub-ppm order. Lower Limit of Determination (LLD) of As was 0.1 ppm order and Sb was 0.01 ppm order.
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  • Effect of YAG Laser Cutting on Stretch-flangeability of Ultra High Strength TRIP Sheet Steel with Bainitic Ferrite Matrix

    pp. 351-356

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    DOI:10.2355/tetsutohagane.94.351

    Effect of YAG laser cutting on stretch-flangeability of 0.2C–1.5Si–1.5Mn (mass%) ultra high-strength TRIP-aided sheet steel with bainitic ferrite matrix (TBF steel) having different martensite start temperatures, which were austempered at 375 or 450°C, was investigated for automotive applications. Hole notches of 5 mm diameter were produced by YAG laser cutting or mechanical punching for hole-expanding test. The stretch-flangeability was evaluated using hole-expanding ratio (λ).
    In TBF steel, laser cutting resulted in much higher stretch-flangeability than mechanical punching. The hole-expanding ratio (λ) of TBF steel austempered at 375°C in the case of laser cutting at average powers between 50 and 100 W was higher than that at 450°C, and also higher than mechanical punching. Furthermore, the strength–stretch-flangeability balance (TS×λ) of TBF steel austempered at 375°C showed the highest stretch-flangeability by laser cutting at 100 W. We found that compared with mechanical punching, YAG laser cutting contributed to the improvement of the TS×λ of 1100 MPa class TBF steel with fine bainitic ferrite matrix.
  • Evaluation of Solidification Cracking Susceptibility in Alloy Tool Steel Considering Dependence of Primary Phase Selection

    pp. 357-362

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    DOI:10.2355/tetsutohagane.94.357

    The solidification cracking susceptibility with the dependence of the selection of the primary phase was clarified with the Trans-Varestraint test, since the solidification mode of alloy tool steel (SKD61) was transited from FA mode (L → L+δ → L+δ+γ → L+γ→γ) to A mode (L → L+γ → γ) at high solidification velocity. It was obtained that the Brittle Temperature Range was enhanced to 587K for A mode while it was 105K for FA mode in the augmented strain of 2%.
    In order to clarify the change of dendrite morphology during the solidification process, the liquid tin quenching was curried out. Though the interdendritic microsegregation can be reduced due to the dendrite arm development, the solidification cracking susceptibility was sensitized in A mode solidification. Therefore, the selection of the primary phase is extremely important.
    The effect of primary phase selection on the interdendritic microsegregation was theoretically proven using the solidification velocity dependence of microsegregation model taking into the diffusion of the solute in the solid phase. It was found that the solidification cracking susceptibility obtained by the Trans-Varestraint test can be simply evaluated as the influence of the mode transition below the solidification velocity of 10 mm s−1 and the reduction of Si, P and S content can be effective on decreasing the risk of solidification crack.
  • In-situ Observation of Ferrite Plate Formation in Low Carbon Steel during Continuous Cooling Process

    pp. 363-368

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    DOI:10.2355/tetsutohagane.94.363

    In-situ observation of austenite-to-ferrite transformation in low carbon steel was conducted with a laser scanning confocal microscope. Development and kinetics of ferrite plates during continuous cooling process were studied. It was in-situ observed that the ferrite plates nucleated at either austenite grain boundary or allotriomorphic ferrite, and grew with keeping the Kurdjumov–Sachs orientation relationship with prior austenite. Surface relief was induced by the formation of ferrite plate. When the ferrite plate nucleated at pre-existing grain boundary ferrite, gradual change in growth direction by the sympathetic nucleation was confirmed both by the observation and EBSP analysis. Temperature dependency of the observed growth rates of the plates was in a good agreement with the Zener–Hillert model, which indicates the growth is controlled by the diffusion of carbon.
  • CDM Project Design for Introducing Coke Dry Quenching Equipment in Shanxi Province of China

    pp. 369-375

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    DOI:10.2355/tetsutohagane.94.369

    This paper provides the design of a Clean Development Mechanism project at the coke industry in Shanxi province, China. The target of this project is to reduce emission of carbon dioxide by installing coke dry quenching equipment into mechanical coke ovens of Shanxi Antai Group Co., Ltd. This paper demonstrates how the anthropogenic emission of carbon dioxide is reduced by this project activity below those that would have occurred in the absence of CDM project. Moreover, this paper shows that this project achieves not only emission reduction of carbon dioxide but energy saving, water saving and emission reduction of other pollutants such as sulfur dioxide.
  • Construction of WEB Sales Information System for Re-roll Maker

    pp. 376-381

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    DOI:10.2355/tetsutohagane.94.376

    Recently many companies try to promote SCM (supply chain management). The objective of SCM is to maximize the operation efficiency covering the entire process of supply chain and minimize the loss opportunity of sales.
    Because of production lead time of re-roll maker is generally longer than crude steel maker, it is more effective to introduce SCM to re-roll maker.
    Toyo Kohan, which is one of the re-roll makers, has been promoted SCM since 2002. Until now, we have established the consistent production control system, hot band procurement system and business support system for SCM. These systems have performed very well so far. As for the next step of promoting SCM, we have developed WEB sales information system to make closer relation with our customers. Using this system, we can accept orders, provide shipping and stock information and exchange delivery information with our customer. This new system has been introduced 2005. This paper is described outline of this system.

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