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

Tetsu-to-Hagané Vol. 93 (2007), No. 10

  • Effects of Tuyere Gas Flow Rate and Deadman Properties on Discontinuous Behavior of Descending Solid and Gas Static Pressure in Blast Furnace—Experimental Analysis by a Three-Dimensional Cold Model—

    pp. 615-624

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    DOI:10.2355/tetsutohagane.93.615

    In low reducing agents operation of blast furnace, it is considered that deadman gas permeability would become low due to fines accumulation around or in the deadman, which would cause unstable behavior of solid and gas. For the stable operation, especially in high productivity operation, the problem must be overcome. A scale-down three-dimensional cold model of blast furnace with a device capable of changing deadman physical properties such as the permeability and height, was used for this study. The effect of gas flow rate/velocity and deadman properties on both the unstable/discontinuous behavior and the solid flow pattern, is analyzed experimentally. In such a situation that gas is impossible to penetrate from the raceway inside the deadman and further bridging is formed over funnel flow channel in Bosh to Belly region, the discontinuity increased with increasing of gas flow rate and gas velocity. The more the gas impermeable wall is high, the more the discontinuity with bridging becomes severe. If the gas impermeable wall height is lower or deadman gas permeability is well, the discontinuity decreases, the solid bed becomes more homogeneous with dense packing state and solid plug flow region enlarges in the lower part. As a result, maintaining gas permeability of deadman in a good state and controlling deadman height lower might be essential for the stable operation.
  • Transfer Control of Conveyers in Ore Yard by Autonomous Decentralized Agents

    pp. 625-633

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    DOI:10.2355/tetsutohagane.93.625

    In steel works, iron ores are stored in ore yard and sent to various plants in down stream according to transfer requests. To attain stable operations of steel works, it is necessary to keep a certain safety stock level in ore tanks of all plants. To attain this purpose, a novel ore transfer routing method has been developed based on a decentralized agent method. In case of disaster such as a big earthquake or a big fire, damages in the facilities of industrial complex may be unavoidable. In this paper, a decentralized optimization method is tested if it is able to cope with such emergencies. A decentralized agent corresponding to the kind of ore makes its own transfer route plan exchanging information with others. As the application of the proposed method, transfer scheduling in ore yard in steel works are made in case of destruction of the transfer facilities. Further, application of the proposed route planning method to the analysis of distribution of transfer loads for conveyers is described.
  • Establishment and Problem of the Observing System for Boron in Steels by Alpha-particle Track Etching Method Using Pneumatic Tube of JRR-3 and JRR-4

    pp. 634-641

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    DOI:10.2355/tetsutohagane.93.634

    The addition of small amount of boron to steel is often employed to improve various properties of steel, but there are still many uncertainties in the behavior of boron in steel. It is necessary to clarify the precipitation and segregation behaviors of boron to develop advanced steels. Alpha-particle track etching (ATE) method is effective to observe the behaviors of boron, but as the irradiation equipment of Japan Atomic Energy Agency (JAEA) has been more intensively used for medical research and treatment purposes recently, time available for the ATE method has been limited. In this study, ATE method using the pneumatic tube is investigated to make the analysis of boron in steel easier under such condition.
    Results indicate that JRR-3 “PN-3” equipment of JAEA is the most applicable to the ATE method using the pneumatic tube. Since the ratio of cadmium of PN-3 is 290, the thermal neutron flux is sufficiently high with low level of background. Boron containing precipitates can be detected as dark spots and the grain boundary segregation of boron as dark lines. It is found, however, that the size of the spots in ATE images is not exactly the same as that of actual precipitates. When the ATE images are compared with TEM images using carbon extraction replica, borides are exaggerated as about hundred-times larger precipitates in the ATE images.
  • Microstructure of Oxide Scale Formed at Early Stage of Oxidation on 17%Cr-Mn-Ni Austenitic Stainless Steels

    pp. 642-648

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    DOI:10.2355/tetsutohagane.93.642

    Microstructure of oxide scales formed at early stage of oxidation of 17%Cr-Mn-Ni austenitic stainless steel was examined using SEM and TEM. Samples were oxidized at 973 to 1373K for 1 to 15 min. Nodules were observed on the surfaces of specimens oxidized at 1173K. The nodules were composed of two layers which were Fe oxides and Fe-Cr-Mn oxides rich in Cr, respectively. The other scales were composed of two layers of Fe-Cr-Mn oxides with different compositions. In the specimens oxidized at 973 and 1373K, no noduls were observed on the surfaces. The scales were composed of three layers after oxidation at 1373K for 1 min. The first layer consisted of Fe-Mn oxides with spinel structure, the second one consisted mainly of Cr oxides with corundum structure, and the last one consisted of Cr-Mn oxides. It is considered that Cr-Mn oxides with spinel structure, which result in the loss of resistance to oxidation, are formed under Cr2O3 layer which is formed at earlier stage of oxidation. Moreover, the oxide scale was characterized by uneven interface of the second layer and the last one.
  • Prevention of Austenite Grain Coarsening of Carburizing Steel during Carburizing by Mn Content Optimization and its Improvement Mechanism

    pp. 649-654

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    DOI:10.2355/tetsutohagane.93.649

    Carburizing steels are often used for automotive drive train parts which require high fatigue strength and impact value. Prevention of austenite grain coarsening of these steel parts during carburizing is an important issue for exerting high performance. In this study, with a view to preventing the grain coarsening during carburizing, influence of Mn content on grain coarsening temperature was investigated for Ti-modified carburizing steel with ferrite and pearlite microstructure. It was found that grain coarsening temperature was elevated more than 50K by reducing Mn content from 0.8 mass% to 0.4 mass%. This is attributed to the elevated Ar3 point due to lower Mn content, where ferrite and pearlite microstructure is coarser prior to the carburizing and initial austenite grain is preferably coarse during carburizing. This result showed that the reduction of Mn content in carburizing steel was effective to prevent grain coarsening during carburizing when the microstructure prior to carburizing was controlled as ferrite and pearlite by hot forging, controlled cooling after hot forging, normalizing or full annealing.

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