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

Tetsu-to-Hagané Vol. 98 (2012), No. 7

  • Effect of Coke Reactivity on Sinter Softening-Melting Property by Simultaneous Evaluation Method of Carbonaceous and Ferrous Burdens in Blast Furnace

    pp. 331-340

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    DOI:10.2355/tetsutohagane.98.331

    In future blast furnace operation which aims at low carbon consumption, it is indispensable to optimize the quality of carbonaceous and ferrous burdens, not evaluations of each individual but both sides of them considering interactions under the coexistence. Therefore, a simultaneous evaluation method of carbonaceous and ferrous burdens at cohensive zone of blast furnaces by softening-melting test which simulated the temperature profile in blast furnaces determined by reactivity of coke was developed. The effect of sinter ore reducibility and coke reactivity on sinter soften-melting property at cohensive zone of blast furnaces were evaluated. With increasing CRI, coke reactivity, gasification start temperature lowers as a result of increasing the reduction rate of sinter at 900∼1000°C and increasing softening shrinkage resistance at the initial stage of the shrinkage near 1200°C.
  • Analysis of Heat and Mass Transfer in a Packed Bed by Considering Particle Arrangement

    pp. 341-350

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    DOI:10.2355/tetsutohagane.98.341

    Low reducing agent operation of large blast furnace has attracted a special attention from the background of the global warming. Because the coke ratio is reduced in this operation, causing a huge local ventilation resistance that causes operational problems, it has become increasingly necessary to understand the operation of blast furnace based on non-empirical phenomena. Among the most promising numerical approaches is a combination of the discrete element method (DEM) and computational fluid dynamics (CFD). In this study, particle-based model was newly developed, which considers heat transfer, mass transfer and chemical reactions in the shaft part of blast furnace. It became possible to analyze the three-dimensional discontinuous phenomena among particle with gas flow.
    Because this model was developed to expand the spatial scale more than conventional analysis, the discontinuous factors made it possible to simulate by the behavior of discrete particles. The particle arrangement and the packed bed structure were evaluated for studying the flow structure, temperature and composition distribution. Remarkable change in the heat and mass transfer characteristic appeared in the interface between coke and ore layer, and near the wall. The ore and coke particle mixture system, which was expected to improve reducing rate due to the dense packing, is relatively-ineffective. Rather, a low permeability resistance improved reducing rate, it means convection effect was larger. Degree of freedom of particle arrangement is high, and its large influence on temperature and reaction distribution, it was able to show the usefulness of this model.
  • Formation of Fine Macrostructure in Ferritic Stainless Steel

    pp. 351-357

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    DOI:10.2355/tetsutohagane.98.351

    Effect of Mg and Ti addition on the solidification macrostructure of high purity ferritic stainless steel was evaluated in order to obtain the fine grains. In this work, columnar to equiaxed transition could not be obtained by the addition of Mg and Ti. This is due to the small constitutional undercooling in this alloy system. However, fine columnar grains were obtained by adding Mg and Ti. It is thought that the larger number of inclusion particles for heterogeneous nucleation is related to obtain the finer grain structure at the initial stage of solidification with large undercooling. Moreover, grain selection behavior of columnar grains has been also analyzed in this work.
  • Machinability Improvement and Its Mechanism in SUS304 Austenitic Stainless Steel by h-BN Addition

    pp. 358-367

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    DOI:10.2355/tetsutohagane.98.358

    In order to improve the machinability of Type 304 austenitic stainless steels, 0.016 mass % boron and 0.2 mass % nitrogen were added, and hexagonal boron nitride (h-BN) particles (1∼5 μm diameter) were precipitated. During turning with cemented carbide insert, cutting force and tool wear were reduced by h-BN precipitation, especially at higher cutting speed of more than 40 m/min. The reduction of cutting force seems to be due to the internal lubrication effect of h-BN in chip shear region and deformation flow layer, along with the lubrication between chip and carbide tool. Better disposability of chip and suppression of tool wear were also achieved by h-BN precipitation. Good machinability of h-BN precipitated Type 304 steel was also found in drilling and sawing with high-speed steel tools.
  • Numerical Analysis Model of Electric Resistance Welding Pipe

    pp. 368-377

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    DOI:10.2355/tetsutohagane.98.368

    Electric Resistance Welding (ERW) pipe is widely applied for structural and mechanical use because of its simple process and high productivity. It is very important to decrease welding defects of ERW pipe because it has been requested high quality as same level as seamless steel pipes recently. Although ERW process is simple, relationships of the defects and its process conditions have not been cleared definitely. It is difficult to make clear effects of each controlled parameters of ERW, because some controlled parameters cooperate to affect the welding condition. Numerical analysis model is very useful method to study the effect of only one factor, but these are a few studies of numerical analysis model of ERW process. To quantitatively calculate ERW using induction heating, it is necessary to use non-linear magnetic property, but theses previous analysis models calculated with linear magnetic property. In this study, 3-dimensional numerical analysis model of ERW process using non-linear magnetic property has been developed and studied the influence of controlled parameters of ERW process on the welding conditions. Temperature distribution of welding edge calculated by this model agreed with the shape of heat affected zone, and it is revealed that V-angle and impeder core position strongly effect the welding power and the heating condition.
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  • Analysis of Governing Factors of Stretch Flange-Ability of Hot-Rolled High Strength Steels on the Basis of Fracture Mechanics

    pp. 378-387

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    DOI:10.2355/tetsutohagane.98.378

    In order to clarify the governing factors of stretch flange-ability, a study to elucidate the mechanism of crack growths on pierced edges during hole- expanding tests was carried out and the following conclusions were obtained.
    1) In the beginning and the middle stage of crack growth, cracks on the pierced edge propagate through its thin surface where a large strain has been introduced by piercing. On the following final stage one of them grows rapidly into deeper area where the material is not or only slightly strained by piercing. Hole-expansion ratio is characterized by the final rapid crack growth.
    2) Materials with good stretch flange-ability have strong crack growth resistance which can be measured by the test method based on fracture mechanics. This is due to the fact that stretch flange-ability is characterized by the final rapid growth of edge cracks and its occurrence is basically dependent on the crack growth resistance based on fracture mechanics.
    3) Thus measured crack growth resistance makes it possible to evaluate a material property which is strongly linked to stretch flange-ability of hot rolled high-strength steel sheets with smaller data scatterings than hole-expansion ratios.

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