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

Tetsu-to-Hagané Vol. 103 (2017), No. 2

  • Recent Progress of Line-profile Analyses for Neutron or X-ray Diffraction

    pp. 73-85

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    DOI:10.2355/tetsutohagane.TETSU-2016-085

    Several methods on single-peak and multi-peaks line-profile analyses for neutron or X-ray diffraction are critically reviewed. Compared with deconvolutional methods like the classical Williamson-Hall method and the modified Warren-Averbach method combined with the modified Williamson-Hall plot, a recently developed convolutional multiple whole profile (CMWP) fitting method enables to provide the density, arrangement and character of dislocation and crystallite size reasonably. Elasto-plastic deformation behavior in austenite, ferrite, martensite and two-phase steels are studied using such profile analyses, revealing that flow stress is dependent not only on dislocation density but also its arrangement. In particular, in situ neutron diffraction with the CMWP analysis is powerful to monitor microstructural changes during deformation and/or heat treatment. For the evaluation of crystallite or grain size, diffraction, small angle scattering and Bragg edge imaging should be employed taking their applicable length scales into consideration.
  • Optimization of Coke Mixed Charging Based on Discrete Element Method

    pp. 86-92

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    DOI:10.2355/tetsutohagane.TETSU-2016-056

    To achieve stable operation of high ratio coke mixed charging, it is important to control coke segregation behavior in mixed layer at blast furnace top. In this study, the effect of charging conditions and burden particle diameter of mixed coke ratio at blast furnace top were analyzed by numerical model based on discrete element method (DEM). Rolling friction coefficient was calibrated by experiment and calculation. Then, segregation behavior of coke particle was numerically investigated by using above calculation parameters. As a result, following findings were obtained.1)At reverse tilting and broad range charging pattern of rotating chute, granular flow to the furnace center was interrupted and mixed coke particle was distributed uniformly for the direction of furnace radius.2)Coke segregation in mixed layer was decreased by lowering particle diameter ratio between coke and sinter. Therefore, for the improvement of coke mixed ratio in mixed layer, control of particle diameter of coke and sinter is effective.
  • Electrochemical Hydrogen Permeation Test under Controlled Temperature and Humidity after Outdoor Exposure at Beijing, Chongqing and Okinawa

    pp. 93-100

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    DOI:10.2355/tetsutohagane.TETSU-2016-096

    Electrochemical hydrogen permeation tests were carried out under controlled temperature and humidity using pure Fe sheet specimens outdoor-exposed at Beijing and Chongqing, China and Okinawa, Japan in order to understand the effect of environmental factors on hydrogen uptake behavior. The maximum hydrogen permeation current densities of the exposed specimens were in the order of Beijing > Chongqing >> Okinawa, while the order of the degree of corrosion of the specimens was Okinawa > Chongqing >> Beijing. X-ray fluorescence analysis showed that the surface concentrations of sulfur on the Beijing- and Chongqing-exposed specimens were higher than that of the Okinawa-exposed specimens, whereas chlorine concentrations of the Beijing and Okinawa-exposed specimens were higher than that of the Chongqing-exposed specimen. Nitrate concentrations of Beijing- and Chongqing-exposed specimens evaluated using nitrate test strips were obviously higher than that of the Okinawa-exposed specimens. It is suggested that air pollutants such as SO2 and NO2 and particulate matters containing inorganic acid ions, likely sulfate and nitrate ions, and possibly organic acids contribute to acidification of rust layer leading to the enhanced hydrogen entry.
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  • Effect of Crystal Plane Orientation on Protrusion Formation during Sputter-Etching of SUS410 Stainless Steel

    pp. 101-110

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    DOI:10.2355/tetsutohagane.TETSU-2016-059

    Argon ion sputter etching was applied to SUS410 stainless steel at a radio frequency power of 250 W for 1.8 ks to 21.6 ks. When the sputter etching time is 1.8 ks, pillars with diameters smaller than 1 μm are formed perpendicular to the surface of the steel. With increasing sputter etching time, cone-shaped protrusions are formed around the root of the pillars, and the base diameter of the protrusions increases to more than 20 μm at a sputter etching time of 14.4 ks. When the sputter etching time is 21.6 ks, the surface of the protrusions is heavily damaged. An EDX analysis reveals that the Cr content of the pillar is larger than that of the matrix. In addition, an EBSD analysis shows that the protrusions are formed preferentially on the grain surface with {110} plane where the atomic density and sputtering yield are larger than {100} and {111} planes. These facts suggest that the (Cr, Fe)23C6 carbides that are precipitated near the surface of the {110} plane grow more stably as the pillars perpendicular to the plane without being removed by sputtering, i.e. higher temperature, higher temperature gradient and vacancy-density gradient than those of the other planes seem to have promoted the stable growth of pillars by fast diffusion of Cr and C from interior of the grain to the bottom of pillars. The successive diffusion of Cr and C to protrusion surface should be the reason for the stable growth of cone-shaped protrusions even after the sputter shrinkage of the pillars.
  • Heat Recovery Process from Packed Bed of Hot Slag Plates

    pp. 111-118

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    DOI:10.2355/tetsutohagane.TETSU-2016-087

    Reduction of CO2 emissions from the steelmaking process is strongly required for prevention of global warming. One promising heat resource that is estimated to have great potential for energy saving is the waste heat of steelmaking slag, which has a temperature of above 1 673 K in the molten state. This molten slag can be solidified in a plate-like shape by feeding it on the surface of water-cooled rolls, and the heat of the plate-like slag can be recovered easily in spite of its low heat conductivity. When these hot slag plates are packed in a slag chamber, the heat of the slag can be recovered by heat exchange with a counter current gas flow. Because the efficiency of gas-slag heat transfer changes depending on the shape of the packed slag, it is difficult to estimate the efficiency of slag heat recovery without evaluating the accuracy of the heat transfer coefficient in the bed. In this work, the effect of the slag shape on the accuracy of the heat transfer equation was evaluated by conducting both laboratory-scale and pilot-scale slag heat recovery experiments and performing a fitting analysis by using a slag packed bed heat transfer simulation model. A comparison of the experimental results and calculation results confirmed that the heat transfer coefficient can be estimated by using Johnson-Rubesin’s equation modified by a correction factor in case the packed materials are plate-like. The effect of the correction factor on the efficiency of slag heat recovery at the industrial scale was also estimated.

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