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

Tetsu-to-Hagané Vol. 96 (2010), No. 4

  • Influence of Potassium Addition on Self Reaction Behavior of Coal Composite Iron Ore Hot Briquettes under a Blast Furnace Simulated Heat and Load

    pp. 141-149

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    DOI:10.2355/tetsutohagane.96.141

    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.
    In this work, influence of coal brand and potassium addition (0.4 mass% as K2O) on self reaction behavior of the briquettes under a blast furnace simulated heat and load was investigated to explore more efficient blast furnace operation.
    The shrinkage of briquettes during reaction and the crushing strength of briquettes after reaction corresponded mostly to their reaction behavior with or without potassium.
    Both gasification of coal and reduction of iron ore during self reaction of briquettes were evaluated and it was found that the former rates were a little smaller than the latter ones as a whole, irrespective of the coal brand and addition of potassium.
    Gasification and reduction of lower rank coal bearing briquettes occurred in lower temperature than those of higher rank coal bearing briquettes. Inversely, the carburization and melting of the latter briquettes proceeded at lower temperatures than those of the former briquettes.
    The catalytic effect of potassium on gasification and reduction was more remarkable for higher rank briquettes than lower rank briquettes. Moreover, potassium enhanced the softening, carburization and melting of both rank briquettes at lower temperatures.
  • Reaction Characteristic of Woody Biomass with CO2 and H2O

    pp. 150-155

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    DOI:10.2355/tetsutohagane.96.150

    Objective in this study is to elucidate the fundamental gasification characteristics for carbonaceous resources. Effects of temperature and gaseous agents on the gasification characteristics of carbonaceous materials were experimentally and theoretically studied by the gasification of woody sawdust, using an electrically heated drop tube furnace. Results of the co-gasification of CO2 with H2O were compared by the gasification by a single gaseous agent such as CO2 or H2O. As a result, H2 and CO concentrations increased with an increase of temperature. CO concentration under the co-gasification condition produced more than that under the single gasification condition. The H2 formation showed the opposite tendency to the CO formation during the co-gasification. This synergy effect was also elucidated theoretically by the simulation of reaction kinetics. The simulated temperature indicating the maximum synergy effect on CO formation agreed well with that obtained by the experiments.
  • Influence of Surface Oxide Scale of Fe–Cr Alloy on Tool Lubrication Characteristic during Hot Rolling

    pp. 156-161

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    DOI:10.2355/tetsutohagane.96.156

    The surface oxide scale formed on steel products plays an important role of lubricating behavior during steel making process. However, there are few reports in detail about the influence of the oxide on lubricating properties. To investigate the effects of oxide scale of Fe–Cr alloy on lubricating properties, hot rolling test was carried out. As a tool material SKD61 was used. In order to change the scale structure of Fe–Cr alloy, dry air and steam containing gas were used as oxidation atmosphere condition.
    In case of the oxidation in wet atmosphere, Fe2O3, Fe3O4 and FeO were formed as outer scale, and FeCr2O4 and FeO were formed as inner scale. On the other hand, for the oxidation in dry air, the scale structure were Fe2O3 and Fe3O4 for outer scale, and FeCr2O4 and Fe3O4 for inner scale. In case of oxidation in wet atmosphere before rolling, the scoring of hot work piece (Fe–Cr alloy) and tools (SKD61) was reduced. TEM observation suggested that surface scale containing FeO was deformed during hot rolling with hot work piece, and then all the surface of hot work piece was covered with scale. The reason for the improvement of scoring behavior by wet atmosphere was thought that FeO on hot work piece (Fe–Cr alloy) prevented the contact with tools (SKD61).
  • Change in Yield Strength of Ultra Low Carbon Steels with Cr Addition

    pp. 162-171

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    DOI:10.2355/tetsutohagane.96.162

    The relationship between ferrite grain diameter and upper yield strength was investigated for cold-rolled and annealed ultra low carbon steel sheets containing various chromium contents from 0 to 23%. The upper yield strengths were dropped with annealing temperature and the tangent of the change in the yield strength was decreased with increasing in chromium content. The coefficient in Hall–Petch equation decreased linearly with chromium content. This is attributed to lowering solute carbon content at grain boundaries with precipitation of chromium carbide since the decrease was not due to ferrite region hot-rolling nor to α′ phase precipitation in high chromium steel. While friction stress (σ0) in Hall–Petch equation of air-cooled sheets after annealing showed the minimum at chromium content of 5%, σ0 of the lower chromium content steels increased and became to show linear relationship for chromium content after 150°C aging. This result indicates that σ0 increases with chromium content by solid solution strengthening. The reason why the minimum σ0 is exhibited in the 5% chromium steel air-cooled after annealing is that the amount of decrease in σ0 by retardation of aging during air-cooled process is larger than that of solid-solution strengthening by chromium.
  • Influence of Heat Treatment on Long Term Creep Properties of 9Cr–W–Mo–V–Nb Steel

    pp. 172-181

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    DOI:10.2355/tetsutohagane.96.172

    This paper describes the effect of heat treatment on long-term creep properties of 9Cr–W–Mo–V–Nb steel which in the specification of ASME Grade 92 as a part of development of high Cr steel for fast breeder reactor (FBR). The effects of normalizing temperature and tempering temperature and time on long term creep properties were investigated from the viewpoint of microstructures. Creep strength increased with increase in normalizing temperature from 950 to 1200°C. The microstructural factors that improve creep strength are increased amount of MX which precipitated during tempering process and increased dislocation density. In addition, coarsening of prior austenite grain size also contribute to increasing creep strength. Although creep rupture time of 780°C–1 h tempering specimen was greater than that of 700°C–1 h and 750°C–1 h tempering specimen in a long term region exceeding 20000 h at 650°C, creep ductility and reduction of area of the former remarkably degraded compared to those of the latter. Higher normalizing temperature and lower tempering temperature and/or shorter tempering time are desirable for long life plant of which material needs superior creep strength and ductility.
  • Development of Friction Stir Welding Apparatus for Steels

    pp. 182-184

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    DOI:10.2355/tetsutohagane.96.182

    Friction stir welding (FSW) is a relatively new solid-state joining process primarily for aluminum alloys. FSW process can also be applied to the welding of a variety of other materials, including magnesium alloys, titanium alloys, stainless steels and metal matrix composites. While considerable experimental work has been done in FSW, there is little published information about FSW apparatus for steels. The development of new FSW apparatus for steels needs to proceed with caution and attention to detail and the reduced cost and time.
    The objectives of this study are to develop a FSW apparatus for steels and to discuss some initial results on FSW of mild steel.

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