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

Tetsu-to-Hagané Vol. 101 (2015), No. 3

  • Direct Determination of Standard Gibbs Energies of the Formation of 4CaO·P2O5 and 3CaO·P2O5 by Transpiration Method

    pp. 169-176

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    DOI:10.2355/tetsutohagane.101.169

    The standard Gibbs energy changes of the following reactions have been measured by using transpiration method;
    4CaO∙P2O5(s) + 5C(s) = 4CaO(s) + P2(g) + 5CO(g)
    ΔGo/kJ = 1624 – 0.953T (± 2.7), (1373 < T/K < 1573)
    4(3CaO∙P2O5)(s) + 5C(s) = 3(4CaO∙P2O5)(s) + P2(g) + 5CO(g)
    ΔGo/kJ = 1946 – 1.193T (± 0.9), (1448 < T/K < 1523)
    The standard Gibbs energies of the formation of 4CaO∙P2O5 (ΔGof,(4CaO∙P2O5)) and 3CaO∙P2O5 (ΔGof,(3CaO∙P2O5)) have been derived as follows;
    ΔGof(4CaO∙P2O5)/kJ mol–1 = – 4765 + 0.965 T, (1373 < T/K < 1573)
    ΔGof(3CaO∙P2O5)/kJ mol–1 = – 4200 + 0.912 T, (1448 < T/K < 1523)
    The reasons for discrepancies from reported values were discussed from the view point of whether the activity of phosphorus is measured directly or not.
  • Effect of Oxygen Enrichment on Mineral Texture in Sintered Ore with Gaseous Fuel Injection

    pp. 177-183

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    DOI:10.2355/tetsutohagane.101.177

    The effects of oxygen enrichment on the mineral texture in sintered ore with the gaseous fuel injection were studied in the laboratory test and its operational results were evaluated in the actual plant.
    The mineral composition is an important factor affect to sinter strength. The mineral composition of sintered ore consists of Fe2O3, Fe3O4, and calcium ferrite and so on. Then, the strength of calcium ferrite is highest of all textures. As the results of sintering test with electrical furnace, calcium ferrite ratio in sintered ore increased with an increase of oxygen concentration in the atmosphere. The increase of oxygen concentration makes calcium ferrite to become stabilized.
    Gaseous fuel and oxygen injection technology have been installed at Chiba sinter plant since 2012. It was confirmed the expansion of the temperature zone between 1,473 K and 1,673 K which is proper for sintering reaction to form the calcium ferrite texture by the gaseous fuel and oxygen injection through the actual plant test. Oxygen enrichment shifted ignition position of coke and gaseous fuel to lower temperature side and the proper temperature zone was expanded. These results denoted the same tendency of the laboratory test results. Moreover, the calcium ferrite ratio of sintered ore increased in the actual plant. As these results, the effects of gaseous fuel and oxygen injection technology were confirmed in the actual machine similarly to the laboratory test.
  • Combustion Rate of Coke in Quasi-particle at Iron Ore Sintering Process

    pp. 184-189

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    DOI:10.2355/tetsutohagane.101.184

    Temperature distribution in layer of the iron ore sintering process is one of the most important factors to decide the sinter quality. To estimate the temperature distribution in sinter layer needs knowledge of coke combustion rate. The purpose of this study is to clarify that coke combustion rate in the fine layer of the quasi-particle with considerations about void ratio and liquid formation. The following results were obtained. Interface chemical reaction rate constant, kc, was independent on the mixing ratio of coke. The higher mixing ratio of coke made the larger effective diffusion coefficient of oxygen, because the higher mixing ratio of coke made the higher void ratio in the sample after coke combustion. The coke combustion rate became small with increasing of liquid formation amount, because liquid phase in quasi-particle prevented oxygen diffusion in there.
  • Real-time Profile Measurement for Reinforcing Bar during Hot-rolling Using High-speed Color Image Processing Camera

    pp. 190-197

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    DOI:10.2355/tetsutohagane.101.190

    We have developed a new real-time profile measurement for rebar during hot-rolling. We have devised a unique optics combined the width measurement by spontaneous light and the geometry measurement by light section method. And then, we have realized the on-site application experiment by using the developed high-speed color image processing camera. High-speed demand was achieved by applying an FPGA real-time parallel-image-processing circuit to a color image. Moreover, taking advantage of simultaneous measurement of width and profile, we have confirmed the actual technologies, such as center position correction, and oscillating removal technique.
  • Spark Discharge Optical Emission Spectrometric Analysis of Inclusions Assisted by Particles Adhering to Sample Surface

    pp. 198-203

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    DOI:10.2355/tetsutohagane.101.198

    A rapid size and composition analysis of inclusions in steel was investigated. We found that the spark discharges hit not only the particles but also the inclusions without rolling up the steel matrix when spark discharge optical emission spectrometry (SD-OES) was applied to the sample adhering particles to its surface. The discharge pulses which held a low Fe emission intensity were selected as inclusion pulses. The size distribution and chemical composition of the inclusions were calculated from the emission intensities of elements constituting the inclusions of these inclusion pulses. We applied the method to alumina inclusions containing MgO, obtaining the size distribution and MgO (mass%) well enough. This method is useful for a relative evaluation of inclusions in a short time.
  • Development of Recrystallization Texture in Severely Cold-rolled Pure Iron

    pp. 204-210

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    DOI:10.2355/tetsutohagane.101.204

    The mechanism of recrystallization texture development is changed by the chemical composition of materials, cold-rolling reduction, and annealing treatment conditions. In this paper, we have discussed the development of the recrystallization texture for cold-rolled iron with 99.8% reduction.
    In cold-rolled iron with 99.8% reduction, the deformation texture was a strong α-fiber (RD//<110>) with high strain. During annealing in a temperature range from 200 to 800˚C, in this highly strained α-fiber, the microstructure started to recover from quite a low temperature. Then recrystallized grains began to appear at 350˚C, and many recrystallized grains were generated at rather random locations. Their textural components were {100}, {211}, {111}, and {411}, which were included in the α-fiber. At 550˚C, recrystallization was completed, and the texture after full recrystallization was similar to that of the cold-rolled iron. This texture developed by unique microstructural changes, which could be classified into continuous recrystallization. The recrystallization texture: α-fiber was changed into the {100}<012> component by selective growth of recrystallized grains following the completion of recrystallization.
  • Proposal of Two-dimensional Local Curvature Multi-vertex Model for Grain Growth Simulation

    pp. 211-220

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    DOI:10.2355/tetsutohagane.101.211

    A local curvature multi-vertex model was developed. This model is a straightforward two-dimensional topological network model based on physical principles that consider the local curvatures of grain boundaries and the grain boundary tensions at triple junctions. Virtual vertices are set on the grain boundaries in order to calculate the driving forces of grain boundary and triple junction migration. Therefore, the accuracy of the developed model is higher than that of the conventional curvature model and the vertex model. In the proposed model, the generation and annihilation of virtual vertices maintained a proper configuration of virtual vertices, and high accuracy is expected with a suitable set of simulation parameters. The proposed model was verified by the grain growth simulation using adequately determined parameters for the artificially generated specimens with 5040 grains.
  • Effect of Cr on Lamellar Spacing and High-Temperature Stability in Eutectoid Steels

    pp. 221-227

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    DOI:10.2355/tetsutohagane.101.221

    In order to clarify refinement of lamellar spacing and high temperature stability of lamellae in pearlite by the addition of Cr, we investigated in terms of supercooling, diffusion coefficient of C and Cr, and spheroidizing of cementite using Fe-0.8%C binary and Fe-0.8%C-Cr ternary steels.
    Equilibrium transformation temperature of pearlite was increased by the addition of Cr. At a fixed pearlite transformation temperature, pearlite lamellar spacing of Cr addition steel was refined by increasing of supercooling compared with Fe-0.8%C steel. On the other hand, in spite of the same supercooling, lamellar spacing was refined by increasing of Cr content. This is caused by decreasing of the diffusion coefficient of C in the austenite by addition of Cr.
    Spheroidizing of cementite in pearlite at high temperature was inhibited by inceasing of Cr content. Spheroidizing rate reduced by the addition of Cr. Spheroidizing of cementite in pearlite by increasing of Cr content was inhibited by increasing of the contribution of diffusion of Cr for the coarsening reaction of cementite.
  • Evaluation of Internal Fatigue Crack Growth Rate Based on a Beach Mark Method

    pp. 228-235

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    DOI:10.2355/tetsutohagane.101.228

    Internal fatigue crack growth rate was measured by using beach marks resulting from repeated two-step fatigue tests for JIS-SCM440 low-alloy steel. This material showed internal fractures under stress ratio of R = 0, and the inclusion sizes of the internal fracture origins ranged from 14 to 40 μm. Two types of beach marks were observed: One was small beach marks indicating internal cracks at an initial stage of fatigue. The other was large ones indicating the internal cracks at a final stage. The internal crack shape at the initial stage was a half-ellipse and asymmetric, while that at the final stage were a circle and symmetric. The asymmetric internal crack shape requires three-dimensional modeling, and therefore, an extremely slow crack growth rate, smaller than the lattice length, is expected in two-dimensional modeling. The growth rate of the asymmetric internal crack was evaluated by d√area /dN instead of conventional da/dN. As the result, the asymmetric internal crack revealed the extremely slow crack growth rate, in spite of the conventional crack growth rate of the symmetric internal crack. The border of the two-types internal cracks was corresponding to conventional ΔKth. Moreover, the growth rate of the asymmetric internal crack showed good agreements with that estimated by Omata’s method based on the conventional fatigue test results. These results support validity of Tanaka-Akiniwa model for the internal crack growth. This research thus proved that gigacycle fatigue life of high-strength steel could be predicted by crack growth life based on Tanaka-Akiniwa model.

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