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

Tetsu-to-Hagané Vol. 95 (2009), No. 8

  • The Evaluation of Coke Strength before/after Solution Loss Reaction for an Actual Coke Image Using Image Based Modeling

    pp. 593-599

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    DOI:10.2355/tetsutohagane.95.593

    In this study, coke strength for an actual microscopic structures before/after solution loss reaction is numerically evaluated using image based modeling. Stress analyses for microscopic structures of coke before/after solution loss reaction at 1173 K are carried out. In the analyses, microscopic structure of coke is assumed to be composed of active components and pores. Analytical results show that the maximum von Mises stress sharply increases with an increase in conversion for solution loss reaction. It is caused by decrease in both pore wall thickness and a reduction in the connection of coke texture by solution loss reaction. The stress distribution closely relates to change of microscopic structures by solution loss reaction.
  • Self Reaction Behavior of Wood Flour Added Coal Composite Iron Ore Hot Briquettes under a Blast Furnace Simulated Heat and Load

    pp. 600-606

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    DOI:10.2355/tetsutohagane.95.600

    The coal composite iron ore hot briquette made by utilizing thermal plasticity of coal is recently developed as agglomerates without binder, which has several advantages to retain high density and strength during reaction at high temperatures. The charge of this briquette to a blast furnace is expected to enable more effectively higher reaction rates at lower temperatures than usual operation. Moreover, utilization of biomass as carbon neutral is essential to construct a sustainable society permitting to conserve global environment and save resources and energies.
    In this work, influence of substituting biomass (Cedar wood flour) for one tenth amounts of coal in hot briquettes was examined by carrying out self reaction tests of the briquettes in a N2 gas steam under heat and load in a laboratory scale blast furnace simulator.
    It was proved that both briquettes with or without biomass could retain an industrial allowable strength beyond 50 kgf/cm2 after reaction, while the addition of biomass enhanced a little more the shrinkage of briquettes in the higher temperatures above 1000°C.
    Both gasification of biomass added coal and reduction of iron ore during their reaction were evaluated and it was found that the former rates were a little smaller than the latter as a whole, irrespective of the addition of biomass.
    Carburization to metallic iron began at nearly 1200°C and both briquettes have been melted down at 1400°C due to nearly carbon saturation in metallic iron with a graphite crucible.
  • Numerical Analysis of Effect of Defects on Fracture Behavior in Metallurgical Coke Using Rigid Bodies–Spring Model

    pp. 607-612

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    DOI:10.2355/tetsutohagane.95.607

    The fracture analyses using RBSM (Rigid Bodies–Spring Model) were carried out for coke models with simple pore in order to examine effect of defects on fracture behavior in metallurgical coke. The discussion about the analytical results summarizes as follows:
    1) Plastic load of coke is affected by pore shape and directions of force around pores. As a result, it is clear that plastic load of coke is concerned with coefficient of stress concentration.
    2) Stress varies with a decrease in pore wall thickness and these interferences affect fracture load of coke. Thus, it is shown that pore and thickness are important factors in coke breakage.
    3) The result of discussion of number density of pore and porosity shows that porosity is the most important factor in coke fracture. In addition, it is shown that diameter of pore and thickness are not as important as porosity in coke fracture.
  • Freckle Formation in Ni-base Superalloys

    pp. 613-619

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    DOI:10.2355/tetsutohagane.95.613

    In order to reduce CO2 emissions from fusel power plants, advanced ultra super critical (A-USC) steam turbine has been developing in Europe, the United States, and Japan. Candidate materials for A-USC steam turbine are Ni-base superalloys because 700°C exceeds the maximum service temperature of heat-resistant ferrite steels. Ni-base superalloys have superior high temperature properties, but they are well known as freckle prone material. One of the keys to the success of A-USC development is the availability of large size ingots for turbine shaft materials. There have been few studies on the productivity of Ni-base superalloys for large ingots. In this study, six A-USC candidate alloys were selected. Freckle tendencies of those A-USC candidate alloys were assessed using a horizontal directional solidification apparatus. The tested alloys tended to freckle in the following order: Alloy230>LTES700>Alloy625>Alloy706>Alloy617-Ti free>FENIX-700>USC141>Alloy617-Ti. We propose that the tendencies could be estimated from liquid density difference calculations.
  • Electron Back Scatter Diffraction Analysis for Inhomogeneous Deformation in a Ferrite–Martensite Dual Phase Steel

    pp. 620-627

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    DOI:10.2355/tetsutohagane.95.620

    Substructures in a ferrite–martensite dual phase steel have been investigated by using a SEM-EBSD technique. Particular attention has been paid on the inhomogeneous deformation developed in the ferrite phase during a tensile deformation, i.e., a kind of deformation bands which enhance work-hardening and uniform elongation. Effects of small angle boundaries (SAB) included in ferrite grains on the stress–strain curve have also been studied.
    Two kinds of a Cr-added low carbon dual phase steel were prepared by different heat treatments. They have almost the same microstructures except the density of SAB in the ferrite phase. The specimen with the lower density of SAB exhibited lower yield strength and larger uniform elongation. SEM-EBSD observation demonstrated that small angle lattice bending due to deformation bands were developed in ferrite phase with tensile strain, indicating a kind of grain subdivision in ferrite grains. Such kind of grain subdivision was commonly observed in large ferrite grains, and it was enhanced in the area neighboring to the hard phase of martensite. It should be noted that mechanical properties of dual phase steels are influenced by such substructures in ferrite grains.

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