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

Tetsu-to-Hagané Vol. 90 (2004), No. 4

  • Three-dimensional Characterization and Analysis of Steel Microstructure by Serial Sectioning

    pp. 183-189

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    In spite of well acknowledged needs for observing microstructure in three dimensions (3D), only sporadic attempts have been made of serial sectioning and 3D visualization of opaque materials microstructure. This situation is changing due to rapid developments of computer hardware and software for data collection and image analysis. This affords an opportunity of 3D characterization and quantification of microstructure with lesser amounts of effort, from which one can check assumptions made in 2D observations, compare results with stereological analyses, precisely determine topological properties and distribution functions, and check more directly various theories in materials science. In this report, recent studies in this area are reviewed with an emphasis on 3D visualization of steel microstructure. A combination of serial sectioning and computer-aided visualization is likely to be used more frequently in materials research in the future.
  • Effects of Volatile Matter of Pulverized Coal on Reducing Agents Rate of Blast Furnace and Combustion Behavior of Coal Mixture

    pp. 190-197

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    The effective calorific value of pulverized coal in a temperature region over 1400°C in the blast furnace was examined, and it was shown that in an operation in which the heat balance in the lower part of the blast furnace was a rate-controlling factor, a pulverized coal having a lower average volatile matter content was effective in lowering the reducing agents rate. However, there is a restriction in the amount of the resource of semi-anthracite coal whose volatile matter is relatively low, we examined a mixed pulverized coal obtained by mixing a high and low volatile matter content coals. The combustion behavior of the mixed pulverized coal was examined by conducting a combustion experiment and a simulation analysis. It was found that when a mixed coal obtained by mixing coals of different volatile matter contents was used, the combustion temperature of the mixed coal deviated toward the high temperature side from a weighted average value of temperatures obtained when each of the coals of different volatile matter contents was burned individually, and that the use of the mixed pulverized coal showed a remarkable effect on the promotion of temperature rise particularly in the initial period. This was because the high volatile matter content coal formed a high-temperature combustion field and promoted the combustion of the low volatile matter content coal.
  • Prediction of As-cast Austenite Grain Size for Near-net-shape CC

    pp. 198-205

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    As-cast austenite grain size (dγ) in low carbon steels has been studied at a cooling rate from 0.1 to 40 K/s. An analytical model has been proposed to predict dγ. The model is based on the classical grain growth theory of Burke-Turnbull, by assuming a normal grain growth with a parabolic law in the temperature range of a γ single phase. The proposed equation is expressed as follows:
    d2γ-d20=Kg[g(Trg)-g(Tf)]/T,
    where Kg is a material constant; Trg and Tf are starting and finishing temperatures of the rapid growth, and g(T) is the dimensionless number indicating the square growth amount below T. The square growth amount of the as-cast γ grain is proportional to the inverse of the cooling rate, T-1. The square growth amount decreases to 20% by phosphorus addition, which decreases Kg and Trg. The prediction agrees well with the experimental data of the continuously cast 100 mm-thick slab and the 2 mm-thick strip.
  • Relationship between Type IV Fracture and Microstructure on 9Cr-1Mo-V-Nb Steel Welded Joint Creep-ruptured after Long Term

    pp. 206-212

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    The long-term creep rupture testing was conducted on 9Cr-1Mo-V-Nb steel welded joint to obtain its creep rupture properties and microstructural changes during creep. From these data the relation between the microstructural change and the initiation and propagation of a creep crack was examined. Creep rupture tests were done at three temperatures of 823K, 873K, and 923K, under the stress ranges of 160-230 MPa, 80-130 MPa, and 40-80 MPa, respectively. In order to investigate the stress and strain distribution of the welded joint specimen that showed the type IV fracture in the low loading stress range at 873K and 923K, finite element method (FEM) analysis was carried out using the creep data of simulated HAZ specimen. The analysis revealed that the stress triaxiality is higher in the fine grained HAZ region adjacent to the base metal than in the other parts. The analysis combined with the experimental results suggests that creep crack would initiate at the fine grained HAZ region adjacent to the base metal at the location of transition in groove angle in the welded joint and would propagate toward the upper part of the V groove along the V groove in the region.
  • Technological Outsourcing in Corporate R&D Activities

    pp. 213-219

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    This paper examines and presents the background of increasing technological outsourcing in corporate R&D activities in the latter half of '90s, as well as future challenges regarding the outsourcing. This paper is based on statistical analysis and a questionnaire survey of corporations, industry by industry.
    The increase in outsourcing occurred because of the needs to speed up R&D processes and to obtain essential technologies which are not internally available have increased. The needs reflect the shift of corporate strategies from possessing superior manufacturing facilities and know-how to trying to be profitable through such means as preemptive commercialization of new products and protection of technologies by patents.
    In various industries, it is becoming imperative to recognize the importance of shifting away from traditional exploitation of internal resources and to improve the corporate-wide ability to evaluate, acquire and utilize external resources.
    In steel industry, the needs to speed up R&D process and to obtain external technologies are not significant. Rather, the role as technology provider for other industires is important. Efforts to provide accumulated technologies to others including overseas companies would be beneficial.
  • Construction of "Kakuro" as an Improved Furnace of "Tatara" for Pig Iron Making

    pp. 220-227

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    The Japanese traditional ironmaking "Tatara" was the unique process using iron sand and charcoal in the world. In 1923, "Tatara" was commercially stopped to operate because of cheaper price of imported pig iron and steel than domestic products. In the middle of Meiji period, Mr. Fuyukiti Obana and Mr. Masateru Kuroda improved the Tatara furnace and constructed "Kakuro" furnace to use waste slag for refining of pig iron and/or iron sand as iron resources. The Tatara furnace was a box type furnace with 1.2 m in height and reconstructed every operation. Three original types of "Kakuro" were developed. The Kakuro furnace in the Ueno works was the same hearth construction with V-type ditch as Tatara furnace and had the high wall of firebricks of about 3 m in height in order to improve the productivity. The 8 tuyers in this furnace were arranged in parallel with the ditch and the higher temperature zone was produced by soft blow. This type of furnace was suitable for using powder iron ore such as iron sand and developed in the Izumo provinces. The Kakuro in the Ochiai works had the square hearth of about 1 m2 with 3 tuyers and high shaft and chimney of firebricks of about 8 m in height. The "Maruro" in the Kadohira works had the round hearth with 4 tuyers and high shaft of firebricks of about 10 m in height. The latter Kakuro and Maruro used lumps of refining slag as an iron resource with hard blow.
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  • Reaction Mechanisms of "Kakuro" for Pig Iron Making from Refining Slag or Iron Sand

    pp. 228-235

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    The Japanese traditional ironmaking "Tatara" was the unique process using iron sand and charcoal in the world. In the middle of Meiji period, Mr. Fuyukiti Obana and Mr. Masateru Kuroda improved the Tatara furnace and constructed "Kakuro" and "Maruro" furnaces to use waste slag for refining of pig iron and/or iron sand as iron resources. Tatara furnace was a box type furnace with 1.2 m in height and reconstructed every operation. The Kakuro furnace was raised about 3 m in height using firebricks to improve the productivity. The Maruro furnace was resemble to a charcoal blast furnace. The Tatara had a fayalite slag including about 60% FeO and about 10% TiO2 and the slag for Kakuro had a few percentages of FeO and about 25% of TiO2 using lime with less basicity of CaO/SiO2 than 1. The component of TiO2 in these slags acts as a flux. The quality of steel made from pig iron produced by "Tatara", "Kakuro" and "Maruro" was excellent in comparison with imported steels. The steel was used as a special steel for roll and blade.

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