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

Tetsu-to-Hagané Vol. 97 (2011), No. 12

  • Influence of Hydrogen on Reaction Behavior of Sinter under Blast Furnace Simulated Condition—II

    pp. 597-603

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    DOI:10.2355/tetsutohagane.97.597

    In order to further reduce CO2 emission in ironmaking, influence of half substitute of hydrogen to bosh gas on reaction behavior of sinter under several blast furnace simulated conditions with different thermal reserve zone temperatures (TRZ temp.) was examined until 1400°C under load by a laboratory reactor.
    In case of TRZ temp. 1000°C, reduction of sinter finalized around 1100°C in the condition of H2 substitute, while the reduction retarded around these temperatures in the condition without H2 substitute. In case of TRZ temp. 800°C, the reduction progressed slower than the former cases as a whole.
    The condition of H2 substitute provided higher carbon contents in sinter after reduction than the condition without H2 substitute. Moreover, the substitute improved the softening melting behavior of sinter by nearly 100°C.
    Analysis by List model indicated that H2 substitute gave less coke rate and less BF productivity, whereas lowering TRZ temp. gave less coke rate and larger BF productivity compared with a basic operation.
    The model analysis also evaluated that less BF productivity with H2 substitute could be improved by making the blast condition higher temperature or oxygen enriched.
  • Oxidation Rate of Molten Steel by Argon Gas Blowing in Tundish Oxidizing Atmosphere

    pp. 604-610

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    DOI:10.2355/tetsutohagane.97.604

    Experiments have been conducted on oxygen gas entrainment by argon gas jets and molten steel oxidation with argon–oxygen gas mixture blowing. Oxygen entrainment behavior of gas jets and gas-phase mass transfer with gas blowing have been evaluated. Reaction rate models for molten steel oxidation with argon gas blowing in oxidizing atmosphere have been presented. The oxidation rates of molten steel with argon gas blowing on the molten steel surface in oxidizing atmosphere and plasma heating in the tundish have been measured and the results have been analyzed from the viewpoints of kinetics. Both oxidation rates have been explained by reaction rate models considering oxygen entrainment by gas jets and gas-phase mass transfer with gas blowing.
  • FEM Analysis of Roller Leveling for Plate

    pp. 611-615

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    DOI:10.2355/tetsutohagane.97.611

    At present, leveling process has been operated depending on experience and intuition of the expert. On the other hand, optimization of leveling condition has been required, and it is urgent to clarify the mechanism of leveling process. Leveling process is divided into the stable and unstable zone, and the mechanism of the two leveling zone are examined. However, the study is carried only experimentally but not numerically. In this paper, the application method of commercial FEM software is clarified and the possibility of leveling plate in the unstable zone is studied. The following results are obtained.
    1) To apply the commercial FEM software, it is necessary to take into consideration of elastic deformation of roller leveler, and work-hardening characteristic of material to simulate the leveling process correctly.
    2) It is confirmed that the variation of plate curvature in the unstable zone can be suppressed by carrying out dynamic control of leveling rolls, from which the possibility of leveling plate in unstable zone is found out.
  • Effect of Trace Oxygen on Charpy Impact Energy of 12% Nickel Steel

    pp. 616-622

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    DOI:10.2355/tetsutohagane.97.616

    In this paper, it was intended to evaluate ductile fracture characteristic of cryogenic steel, especially focused on the effect of trace oxygen, which is important factor as impurity of practical steel, on the Charpy impact energy of 12% nickel steel. Since the ductile fracture characteristics were less investigated as for cryogenic steel such as 9% nickel steel, while the brittle crack initiation and propagation property have been extensively researched. 12% nickel steels were used in this investigation to avoid the difficulty of fracture phenomenon interpretation by accompanying brittle fracture. With decreasing oxygen content from 0.0024 to 0.0009 wt%, Charpy impact energy at the temperature of 77K and 273K, increased in the range of dozens of joule. This tendency reveals that the ductile fracture characteristic of 12% nickel steel is sensitive to the change of oxygen content compared to those of the other steels. With reducing oxygen content, the number concentration of Al2O3 descends, and it leads to the enhancement of resistance to ductile crack propagation, in which Al2O3 acts as the initiation site for void.
  • Effect of Plastic Strain and Preloading on Delayed Fracture Characteristics of High Strength Steel

    pp. 623-630

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    DOI:10.2355/tetsutohagane.97.623

    Plastic strain takes place at the bottom of the thread, when fastening force is applied to the high strength bolts. The effect of plastic strain on the delayed fracture characteristics was studied using conventional strain rate test (CSRT). For this purpose two kinds of methods were used in the experiments: one is applying uniform plastic strain to the specimen before machining notch and the other is preloading of notched round bar (NRB) specimen. The hydrogen content increased as increasing plastic strain and in contrast, the relationship between fracture stress and hydrogen content using CSRT was independent of plastic strain, which indicates that plastic strain increases hydrogen content and results in decreasing fracture stress based on the above-mentioned relation. On the contrary, the preloading affected the fracture nominal stress obtained by CSRT of hydrogen precharged NRB specimen. Using finite element stress analysis, the maximum stress ahead of the notch tip for preloaded NRB specimen was obtained. The relationship between the fracture maximum stress and hydrogen concentration becomes unique irrespective preloading. It is concluded that the relation of local maximum stress—the hydrogen concentration at the delayed fracture initiation site is the material constant and control delayed fracture.
  • Influence of Microstructure of Steel on Diamond Tool Wear

    pp. 631-636

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    DOI:10.2355/tetsutohagane.97.631

    Excessive tool wear occurs when commercial steels are single-point diamond turned. Therefore, the development of diamond turnable steel is expected in the manufacture of molds for complex and precise optical components. As an initiate approach to this subject, various kinds of quenched and tempered steels were turned using single-crystal diamond tools, and tool wear measurement was made with a scanning electron microscopy. As a result, the various amounts of coner wear was observed by the diamond tool, and the width of wear was found to be different in a kind of steels. In order to clear up this cause, constituent phase analysis of the steels used in the turning experiments was carried out by X-ray diffraction. It gave that their microstructures differed considerably from steel to steel and were classified into four group, those are α-ferrite, α-ferrite + γ-austenite, γ-austenite, and α-ferrite + such carbides as Fe3C, Cr23C6 and WC. On the basis of these results, the inductive inference methodology was applied to the tool wear measurement and phase analysis. From the results, the steel whose microstructure consists of particle carbide precipitation on α-ferrite matrix, e.g. JIS SK85, SUS420J2, SKS3 etc., suppresses diamond tool wear because the carbides prevent carbon diffusion into iron in turning of steel.
  • Mechanisms of Forge-and-Welding of Japanese Steel Using “Wakibana” Sparks in Flame as a Start Signal of the Work

    pp. 637-644

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    DOI:10.2355/tetsutohagane.97.637

    “Tsumiwakashi Tanren” is the forge-and-welding process to form a steel block from steel pieces that are produced by Tatara. “Orikaeshi Tanren” is the forge-and-welding process to hold up a steel block to produce a steel plate. Steel blocks were covered with straw ash and mud and heated in blacksmith's furnace. When the temperature of steel blocks increased over 1100°C, the fire flame of charcoal colored yellow followed by orange. The yellow flame was D-line spectrum of sodium with 589 nm wavelength and was a sign of production of molten fayalite slag, so called “Noro”. When temperature increased over 1190°C, small and bright sparks so called “Wakibana” started to appear in fire flame from charcoal. When temperature attained at 1290°C and many “Wakibana” sparks appeared, blacksmith took out steel blocks on a anvil and forged them to weld by hammering. At this time, temperature at the interface of steel blocks increased to about 1470°C by oxidation of iron and decarburization and the surface of steel block melted and wetted. Then, by hammering, “Noro” film was broken and steel blocks easily welded. When small bubbles of CO gas were produced at steel surface by strong force, fine steel particles were caught in CO babbles and oxidized in air to make bright sparks of “Wakibana”. “Wakibana” is a start signal of forge-and-welding process.

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