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

Tetsu-to-Hagané Vol. 94 (2008), No. 4

  • Computer Simulation of the Effect of Center Charging Solid Density or Frictional Property on the Solid Flow and Deadman Behavior in Blast Furnace

    pp. 107-114

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    DOI:10.2355/tetsutohagane.94.107

    A center coke charging method from the top of blast furnace is known for a novel approach to burden distribution and coal combustion. This method is considered as one of the key technologies for keeping gas permeability of deadman in the lower part of blast furnace and producing iron liquid with a stable furnace operation. In recent years, the center charging method is also expected as improving the unsteady behavior with bridging/slipping of solid bed in low reducing agents operation of blast furnace. In the present study, a center charging method with different particle density or friction coefficients is carried out numerically by using a 3-dimensional Discrete Element Method (DEM). Before the numerical analysis, an experimental approach using a two-dimensional cold model is also examined. Alumina sphere was used as representative particle of coke/ore packed bed and the glass sphere was for the center charge. From the experiment, it was found that the height of deadman is reduced dramatically by using the center charging method with the glass sphere. This experimental result was compared with the numerical approach, although the gas flow was not considered in the numerical method. In the numerical results, the void fraction was calculated more precisely compared to the previous numerical two-dimensional calculation. Almost uniform particle flow distribution called a piston flow pattern was fairly maintained by the numerical center charging method, and as the result, the height of deadman was also confirmed reduced numerically compared to the alumina bed only. This result was qualitatively coincident with the experimental flow pattern except for the particle velocity descending faster in the experimental center-charging region, which could be available for the operation of deadman control.
  • Kinetic Analysis of Spherical Wustite Reduction Transported with CH4 Gas

    pp. 115-120

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    DOI:10.2355/tetsutohagane.94.115

    Rapid in-flight reduction of fine iron ore transported with CO, H2 and/or CH4 gas has been studied for direct use of fine iron ore in iron-making process. In this work, the mechanism and the kinetic of the reduction by CH4 gas were accurately investigated with spherical wustite fine particles. The spherical wüstite fine particle as fine iron ore was prepared to simplify the reduction rate analysis. Reduction temperature was varied from 1373 to 1573K. As the result, fractional reduction of spherical wüstite by CH4 gas reached over 80% at 1573K within 1 sec. From the cross section observation of the particle after reduction, it was found that the periphery of the wustite particle was metallized by reducing reaction and un-reacted wüstite core remained inside. Therefore, it was indicated that the reduction progressed topochemically in this experimental condition. In the reduction rate analysis, it was found out that the reduction rate by CH4 was higher than that by H2 or CO. From the carbon concentration analysis, it was found that the phase of the metallic shell during reduction was not only solid state but also liquid state. From the above-mentioned kinetic analysis, it was concluded that the reduction rate determining-step by CH4 was chemical reaction on Fe–FeO interface and the reduction of wüstite was preceded by the carbon dissolved into metallic shell from CH4 gas.
  • Development of Data Analysis System of Angular Dispersive Neutron Diffraction for Stress and Microstructural Parameters in Deformed Steels

    pp. 121-129

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    DOI:10.2355/tetsutohagane.94.121

    A data analysis system has been developed to determine texture, lattice strain, block (or grain) size and dislocation density from neutron diffraction profiles obtained by an angular dispersive method. The texture is evaluated from the integrated area of the curve-fitted quasi Voigt function for experimental profiles. The block size and dislocation density are obtained by profile analyses based on an integral breadth method as well as a Fourier coefficient method. The obtained results of lattice strain, block size and dislocation density are superposed onto the orientation pole figure as output results. The developed system was applied to a cold-rolled SUS316 steel and drawn carbon steel wires to examine its usefulness.
  • Effect of Softening Heat Treatment on Mechanical Properties and Microstructures of Abrasion-resisting Steels

    pp. 130-133

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    DOI:10.2355/tetsutohagane.94.130

    The abrasion-resisting steels are used for structural parts and required for construction machinery parts. Generally, they are so difficult to form the desirable product shape that they must be subjected to a kind of softening heat treatment. In the past, the full annealing treatment with a very extended period of 24 h has been conducted in our production, however, the spheroidizing heat treatment brings about a good machinability with a brief heat treatment time.1) In this study, it is investigated that the effect of the spheroidizing annealing on mechanical properties and microstructure. As a result, we could shorten the heat treatment time and obtain comparable properties to the conventional products by adopting spheroidizing annealing. It was found that, in the proeutectoid ferrite, it is effective to austenitize before spheroidizing period to decrease the yield stress because of coarsening pearlite colony size and spreading the pearlite lamellar spacing.
  • Effect of Surface Roughness of Roll on Coefficient of Friction in Hot Rolling

    pp. 134-140

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    DOI:10.2355/tetsutohagane.94.134

    In order to understand the tribological behavior at the interface between roll and workpice in hot steel rolling, it is important to measure the coefficient of friction and examine the effect of the tribological factors on the coefficient of friction. In this paper, the effects of the surface roughness of roll on the coefficient of friction are investigated by using the tribo-simulatior testing machine for hot rolling developed by the authors. The workpice material used is SPHC. The roll material is SKD11 and the surface roughnesses are 0.1, 0.2, 0.4 and 0.8 μm Ra. The rolling tests are carried out at a temperature of 800°C during a rolling distance of 400 mm, changing the rolling speed from 50 to 70 m/min. The colza oil is used as a base oil and the emulsion concentrations are 0.1 and 3.0%. The coefficient of friction at an emulsion concentration of 3.0% dose not depend on the surface roughness of roll. However, the coefficient of friction at an emulsion concentration of 0.1% decreases with increasing surface roughness of roll up to a surface roughness of 0.3 μm Ra and over 0.3 μm Ra it increases with increasing surface roughness of roll.
  • High-temperature Strength and Microstructure of Strongly Cold Worked Austenitic Stainless Steel

    pp. 141-147

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    DOI:10.2355/tetsutohagane.94.141

    The high temperature strength and the microstructural change of strongly cold worked austenitic stainless steel SUS305 were investigated. 60% cold rolled specimens suggested strong decrease of fatigue strength, creep rupture strength and Vickers hardness (hereafter; hardness) after aging, corresponding to the increase of recrystallized grains. On the other hand, 30% cold rolled specimens suggested less decrease of strength and hardness, and revealed no recrystallization.
    In this study, the microstructure and hardness of strongly deep drawn SUS305 at high temperature were also investigated. On this specimen, similar to 60% cold rolled SUS305, decrease of hardness corresponded to the increase of recrystallized grains. But, since M23C6 precipitations were fine and closely spaced in the material, the recrystallization was delayed. On the other hand, the both materials suggested same relativeness between the softening tendency and recrystallization. Therefore, fatigue strength and creep rupture strength of deep drawn SUS305 should decrease with the recrystallization at high temperature.
  • Effect of Zr Addition on Tensile Property of Fe–Al Based Alloys at Room Temperature

    pp. 148-154

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    DOI:10.2355/tetsutohagane.94.148

    Mechanical properties of thermomechanically processed Fe–33at%Al and –38at%Al intermetallic alloys containing Zr (0.2–1.0 at%) were investigated by means of room-temperature tensile test and hardness test. The Zr-added ternary alloys showed fine-grained microstructure containing large (Fe, Al)12Zr τ1 phase particles, whereas the binary Fe–Al alloys showed a single phase microstructure consisted of coarse recrystallized grains. Yield stress was controlled by Hall–Petch rule and increased with decreasing grain size. Tensile elongation was controlled by the second-phase particles and decreased with increasing the volume fraction of the second-phase particles. Ultimate tensile stress was affected by the second-phase particles when the alloys were composed of fine grain size while it was affected by the grain size when alloys were composed of large grain size. Vacancy hardening which was significant in the alloys with high Al contents (i.e., Fe–38Al) was reduced by introducing the large τ1 phase particles.

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