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

Tetsu-to-Hagané Vol. 94 (2008), No. 2

  • Utilization of High VM Coal in the Reduction of Carbon Composite Iron Ore Agglomerates

    pp. 35-41

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    DOI:10.2355/tetsutohagane.94.35

    Since high VM coal is inexpensive and deposits are abundant all over the world, the use of high VM coal is highly desirable in the carbon composite iron ore reduction process. However, when high VM coal is used, deterioration of DRI strength will occur. In order to solve this problem, different carbonization conditions were applied to high VM coal and different agglomeration methods were tested. As a result, when the non-carbonized coal was used and iron ore/coal composite briquettes were made under high pressure, high strength DRI was obtained. By this method, the porosity was effectively reduced in the carbon composite agglomerates, internal heat transfer was improved, and sintering of reduced metal was promoted.
  • Investigation of Partial Pressure Distribution of Undecomposed NH3 in Carbonitiriding Atmosphere

    pp. 42-50

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    DOI:10.2355/tetsutohagane.94.42

    We have beeen investigating the nitrogen penetration mechanism of high carbon chromium bearing steel JIS-SUJ2 (SAE52100 equivalent) in the carbonitriding process. Our previous research results exhibited that partial H2 pressures and residual NH3, and carbon activity in an ambient furnace atmosphere were the rate-detemining factors of nitrogen penetration. In this study, an atmospheric imbalance of partial NH3 pressure was experimentally analyzed. In addition, distribution map of the partial NH3 pressure was calculated by CFD analysis in which the decomposition reaction rate was take into account. The extrapolated data obtained from CFD analysis corresponds well with the experimental data. Hence, we believe that the CFD analysis is effective in order to control carbonitriding quality and to devise heat treatment furnace structures.
  • Changes of Dislocation Structure and Magnetic Properties in Tensile and Fatigue Deformed Low Alloy Steel

    pp. 51-56

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    DOI:10.2355/tetsutohagane.94.51

    In tensile and fatigue deformed low carbon steels, the magnetic parameters and the total dislocation density were measured. The total dislocation density that was measured by transmission electron microscopy (TEM) reflects the information of cellular dislocation structure. Magnetic parameters, coercive field HC and the coefficient of magnetic susceptibility c had dependency on ρt, written as HC∝ρt1/2 and c∝ρt. These magnetic parameters have simple dependences on dislocation density, and would be useful for nondestructive evaluation of internal structure in practical steel.
  • Mechanical Properties Controlling Ductile Crack Growth of Structural Steel

    pp. 57-65

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    DOI:10.2355/tetsutohagane.94.57

    The effort of this study is to reveal the material properties controlling the resistance to ductile crack initiation and growth (CTOD-R curve) on the basis of the microscopic observation of crack growth, so that the CTOD-R curve can be numerically predicted only from those properties. The crack growth resistance tests using 3-point bend specimens with fatigue pre-crack for two steels provide different ductile crack growth resistance, CTOD-R curve, whereas both steels have the same “mechanical properties” in terms of strength and work hardening. The crack-tip constraint effect, in this case the pre-crack length effect, on the CTOD-R curve is also different between both steels. The observation of crack growth behaviors reveals that micro-mechanisms of ductile crack initiation from fatigue pre-crack and subsequent extension can be different. It is shown that two “ductile properties” of steel associated with ductile damage can control the CTOD-R curve. The one is “critical local strain” evaluated with the notch-tip strain for ductile cracking obtained with bending test of notched specimen, which controls ductile crack initiation of pre-cracked specimen. The other one is “stress triaxiality dependent ductility” obtained with circumferentially notched round-bar specimens subjected to tension, which controls the ductile crack extension for pre-cracked specimen.
  • Construction of Business Support System for Supply Chain Management at Re-roll Maker

    pp. 66-71

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    DOI:10.2355/tetsutohagane.94.66

    With the dramatic increase in demand for steel materials by many foreign countries, especially by China, the supply for steel materials have become more limited than ever before, and this trend is expected to continue for sometime. Therefore many steel companies try to introduce SCM (Supply Chain Management) to respond timely and precisely to market movements.
    The objective of SCM is to maximize the operation efficiency covering the entire process of a supply chain. There are two necessary conditions for applying SCM between several companies. One is that the basic idea of SCM is owned jointly by each company, The other is to create a data base containing records for evaluating SCM. Recently, information technology has developed enough to establish such an information system.Toyokohan has promoted SCM since 2002. Until now, we have established a consistent production and material procurement system. Both systems have performed very well so far.
    As for the next step of promoting SCM, we have developed a new business support system for sales, purchasing and production control departments. This system can provide important and necessary information for SCM and support activities of these departments.

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