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

Tetsu-to-Hagané Vol. 88 (2002), No. 1

  • Effects of Mechanical Offset Agitation on Dispersion of Low Density Particles in Cylindrical Bath

    pp. 1-7

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    A water bath in a cylindrical vessel was mechanically agitated by a stirrer in order to promote dispersion of low density particles in the bath. The motions of the particles were observed with a high-speed video camera. The velocity of liquid flow was measured with a laser Doppler velocimeter. Mixing time was also measured to evaluate the mixing intensity in the bath. Offset stirring was very efficient for uniform dispersion of the particles compared with centric stirring. An inclined vortex caused by the offset stirring was found to significantly shorten the mixing time, and, hence, to contribute to the uniform dispersion.
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  • Coke Properties and Operational Conditions of Blast Furnace to Prevent Coke Degradation in the Raceway

    pp. 8-15

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    Fine coke, which mainly originated in the raceway, has a great influence on the blast furnace operation. Generation behavior of coke fine in the raceway was investigated by the coke combustion experiments and the examination of the coke collected from Chiba No. 5 blast furnace.
    Fraction of fine coke in deadman increased as coke strength decreased, as coke CRI decreased, as flame temperature decreased or blast velocity increased. And influence of coke properties on coke fine generation in the raceway was confirmed from the coke combustion experiments. These results imply that coke was gasified and broke down to generate fine coke in the raceway.
    Mathematical model of fine coke generation in the raceway, which consists of coke gasification and destruction in the transient region and combustion in the dense oxygen region, clarified that high strength coke, high reactivity coke, high flame temperature or low blast velocity decreases in coke fine generation in the raceway.
  • Method of Sinter Pot Test of Evaluation for Dioxins Formation on Iron Ore Sintering

    pp. 16-22

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    The new law concerning dioxins is promulgated in Japan, the iron ore sintering plants enforcing the suppression of dioxins emission. The present paper reports a study on the method and conditions of sinter pot test to evaluate dioxins and Cl content in exhaust gas. Main results obtained are as bellow. Cl is partly trapped on wind box and outlet tube of sinter pot apparatus, but dioxin is not trapped. Repeatability of measured dioxin concentration is as same as ones of NOx and SOx concentration in sinter pot test under the condition of constant flow rate of exhaust gas. Dioxins concentration in sinter pot were in good agreement with one in actual plant. These results conclude that sinter pot test is effective to evaluate dioxins.
  • Mold Flux for High Speed Continuous Casting of Hypoperitectic Steel Slabs

    pp. 23-28

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    High speed continuous casting technique for hypo-peritectic medium thick slab was developed. For mild-cooling of solidified shell, the mold flux was designed to crystallize effectively by new method which gives accurate phase relation between mold flux composition and cuspidine (3CaO·2SiO2·CaF2).
    The results were as follows;
    (1) It was possible to increase casting speed to 5.0 m/min without surface longitudinal cracking on slabs by the developed mold flux of mild-cooling.
    (2) The stability of phase equilibrium between mold flux composition and cuspidine was important to promote crystallization in flux film between mold and solidified shell. Then interaction between F- and Na+ was necessary to be considered for accurate prediction about phase relation between them.
    (3) Because of crystallization in flux film, the top of solidified shell was cooled mildly to be uniform and that resulted in prevention of surface longitudinal crack of slabs.
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  • Influence of Nitride Precipitation on the HAZ Toughness of High Nitrogen Containing Ni-free Austenitic Stainless Steel

    pp. 29-35

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    This work was undertaken to examine the influence of Cr-nitride on impact property in heat affected zone of high nitrogen containing Ni-free austenitic stainless steel. Cr-nitride precipitation of HAZ was simulated to be determined using the isothermal test and the Gleeble test by varying holding time and cooling rate, respectively. Impact toughness was determined by testing Charpy V-notch type impact specimens (55×10×5 mm3) between room temperature and 77K. The time-temperature-precipitation (TTP) diagram for Cr2N precipitation showed that the nose of each C curve (i.e., intergranular, cellular, and transgranular Cr2N) was around 1173K. Cr2N precipitation at holding temperature 1173K occurred sequentially at grain boundaries, by cellular precipitation, and, finally, by transgranular precipitation within the matrix. Amount of intergranular and cellular Cr2N precipitation increased with increasing holding time or decreasing cooling rate. High nitrogen containing Ni-free austenitic stainless steel exhibited excellent impact toughness at room temperature. At 77K, impact toughness was decreased markedly, and ductile-to-brittle (DBT) transition behavior associated with brittle transgranular fracture was observed. Intergranular and cellular Cr2N precipitation reduced impact property of HAZ at room temperature. In addition, embrittlement occurred due to grain boundary separation and fracture through cellular precipitation regions, initiated at Cr2N. However, regardless of amount of intergranular and cellular Cr2N precipitation, impact toughness values of HAZ were not observed at 77K.
  • Fine Precipitates in High Chromium Heat Resisting Steels

    pp. 36-43

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    Microstructural observations were carried out on modified high chromium steels which were subjected to tempering at various temperatures. The kind of identified fine precipitates was mainly influenced by tempering temperature. Large amount of M2X was recognized in the steels tempered at below 993K regardless of its chemical composition. M2X was scarcely identified in the steels tempered at above 1023K. Many MX, however, were recognized instead of M2X in the steel tempered at above 1023K. The composition of M2X was changed by tempering temperature. The amount of vanadium in the M2X increased as tempering temperature was raised. A little amount of fine NbX was identified except for insoluble NbX. During high temperature exposure, the amount of extracted residue increased with time. One of the features of its tendency was that the amount of vanadium gradually increased in the steel tempered at below 933K. Precipitation of fine VX and Z phase were recognized in the steels aged or crept for more than 10000 h at 873K. Fine M2X remained at least for 10000h at around 873K.
  • Analysis of Thin Electroplated Layers by the Bias-current Controlled R.F. Glow Discharge Optical Emission Spectrometry

    pp. 44-47

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    In radio-frequency glow discharge optical emission spectrometry (r. f. GD-OES), a bias-current conduction technique has been successfully applied to the analytical application with higher detection sensitivity. The d.c. bias current can introduce a great many electrons into the plasma, thus leading to an enhancement in the emission intensities through the collisional excitations, whereas the sputtering rate is reduced due to the decreased d.c. bias voltages. This feature can be utilized to improve the information depth in depth profiling by r. f. GD-OES, because of the lower sampling rate as well as the better sensitivity. When nickel electroplated steel sheets were analyzed, the integrated intensities increased by a factor of 30 or more. The information depth in the coating weight analysis could be reduced about 20-fold, compared to that obtained with the conventional measurement.
  • The Origin of MgO Type Inclusion in High Carbon Steel

    pp. 48-50

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