Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 81 (1995), No. 7

  • Direct Observation of a Single Coal Particle Combustion in a Laminar Flow Furnace

    pp. 703-708

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    The experiment on a single coal particle combustion was carried out with a laminar flow furnace to clarify the fundamental combustion mechanism of pulverized coal particles injected into the blast furnace. High speed camera was used to observe the coal particle combustion, and the temperature distribution nearby the coal particle was estimated by the image analyzer. A flame sheet around the particle due to the combustion of volatile matter was observed after the ignition, and it was found that the radius of flame was dependent on the oxygen concentration and coal type. On the basis of these results, it was estimated that the location of the flame sheet of coal particle influenced on the combustion rate through the heat supply from the combustion flame of volatile matter. Moreover, in the case of massive coal injection in a blast furnace, the dispersion of coal particles and the oxygen content nearby the coal particles were considered to be significant on the combustion rate.
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  • Influence of Residual Slag and Steel on the Hot-cycle Operation of the Tundish

    pp. 709-714

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    No.4CC-2nd Strand machine at Kakogawa Works is a single strand continuous casting machine with the hot-cycle operation of the tundish under the hot condition. This caster has been designed for high quality slabs at low cost.
    In this study, in order to prevent oxidation of the molten steel in the hot-cycle operation, the behavior of residual slag and steel was investigated. The Reduction of slag in tundish and the preserving the molten steel in tundish with slag can reduce the inclusion of cast steel. The Build up on the refractories in tundish arised from adhesion and growth of crystalized MgO (MnO) · Al2O3, calcium-aluminate in residual slag.
    Further, the operation without pre-heating under the hot-cycle tundish can prevent the oxidotion of residual metal, which results the clean steel. (the decrease of inclusion)
  • Effect of the Primary Oxide on the Behavior of the Oxide Precipitated during Solidification of Steel

    pp. 715-720

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    Effect of the primary oxide on the behavior of the oxide precipitated during solidification was investigated using Mn deoxidized steel which has primary oxides and soluble oxygen before solidification of the steel. The composition and size of oxides in the continuously cast steels were observed and theoretically analyzed. The results obtained are as follows.
    MnO-FeO and MnO-FeO-Al2O3 oxides were observed. The compositions of the oxides change with cooling rate of the steel and the size of oxide. The Al2O3 content of the oxide at low cooling rate is lower than that at high cooling rate. The Al2O3 content of the oxide decreases with the decrease in the size of the oxide.
    As a result of the theoretical analysis of the oxide behavior during solidification on the basis of a diffusion growth model, it has been found that MnO-FeO oxide is precipitated and grows regardless of primary oxide during solidification and MnO-FeO-Al2O3 oxide grows during solidification as MnO precipitates on the primary oxide which contains Al2O3.
  • Mechanisms of Poor Machinability of Austempered Ductile Iron

    pp. 721-726

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    For the purpose of high strength austempered ductile iron (ADI) has the potential to reduce the size and weight of automotive parts, however poor machinability has made it difficult to achieve broad commercial application.
    To clarify the mechanism of poor machinability of ADI, (i) the chips was analysed by X-ray diffraction, (ii) the cutting front was observed after instantaneously stopping using a quick stop device, (iii) for the turning tool wear was measured and (iv) sawability of material was compared using a saw test.
    The results were as follows :
    In the low cutting-speed range, it was found that strain induced transformation from retained austenite (γR) to martensite (α') occurred, and this corresponded to the poorest machinability in the saw test.
    In the high cutting-speed range.γR →α' transformation was limited to the damaged layer, because the temperature of chips exceeded Md point.
    The tool wear during turning of ADI was generated closer to the cutting edge, as compared with turning of steels. Observation of chip forming state showed that this phenomenon resulted from the following two factors : a) the formation of saw-tooth like chips and the decrease of the tool-chip contact length due to the spheroidal graphite, and b) the increase of cutting force due to the high hardness of the bainitic phase and the damaged layer hardened by the γR →α' transformation.
  • Corrosion Resistance of Surface Modified Poly Vinyl Chloride Coated Steel Sheets by Electron Beam Induced Graft-Polymerization

    pp. 727-732

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    Corrosion resistance of surface modified poly-vinyl-chloride (PVC) coated steel sheets by electron beam induced graft polymerization and corrosion behavior was investigated. The surface modified PVC coated steel sheets by methacrylic acid (MAA modified PVC coated steel sheets) corroded slightly in the degree of white rust occurring after salt spray test.
    After the specimens were dipped in the NaCl solution, SVET and A. C. impedance were measured. The MAA modified PVC coated steel sheets showed negligibly small anodic current at the cross cut area and high resistance maintained at the initial state in comparison with the non-modified PVC coated steel sheets.
    It is assumed that Zn ions eluted from galvanized layer were trapped at the MAA (calboxyl group) layer in the PVC film, and this layer which showed high resistance maintained inhibition of cathodic reaction for PVC coated steel sheets.
  • Cold Model Experiment on Fluid Flow Phenomena in Hot Dip Plating Bath

    pp. 733-738

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    Flow phenomena in a hot dip plating bath were investigated by using cold models with reduced scale of 1/5 and 1/10.The flow pattern, mean velocity components, root-mean-square value of turbulence components and Reynolds shear stress in the bath were measured using a hot-wire anemometer and a two-channel laser Doppler velocimeter (LDV). The flow pattern in the bath was three dimensional. Main flow induced by belt motion on the entry side moved into the exit side and subsequently returned along the side walls and the bottom wall to the entry side. A part of the flow returning along the side walls to the entry side entered from the edges of the belt into the region enclosed with the belt. The flow pattern in the region enclosed with the belt was also three dimensional. The flow pattern in the whole bath was in good agreement with that suggested by mean velocity vectors measured with the LDV. Mean velocity components and the root-mean-square value of turbulence components were altogether low in the almost all part of the entry side region except near the belt. A great amount of dross accompanied with flow in a practical hot dip plating bath seems to exist in this region. As the Reynolds shear stress was very high in the vicinity of the strip extending from the sink roll to the exit side, the dross would be vigorously disturbed and dispersed there.
  • Effect of the State of Cu in Hot-bands on r-value of Cu-added Extra Low Carbon Cold Rolled Steel Sheets

    pp. 739-744

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    The effect of morphorogy of Cu phase before cold rolling on r-value of Cu-added extra low carbon Ti-added steel sheets was studied.
    The morphorogy of Cu phase can be affected by the hot-band heat treatment temperature and the cooling rate after the heat treatment. When hot-bands are heat treated at 550°C or at 800°C and slowly cooled, fine Cu-rich cluster which strengthens the steel is formed. When heat treated at 700°C, ε-Cu is formed but Cu-rich cluster is not formed at the cooling rate range examined. When hot-bands are heat treated at 450°C or 800°C and rapidly cooled, Cu is in solid solution.
    The r-value of annealed steel sheets is affected by the structure of Cu precipitates before the cold rolling. When Curich cluster is formed, the r-value is low according to the decreasing of the intensity of {554} <225> in recrystallization texture. When Cu is in solid solution or ε-Cu is formed before cold rolling, the pole figures of annealed sheets are {554} <225> type and r-value is kept high.
  • Effect of Holding Time after Forging on Grain Growth of Austenite in Steel for Large Scale Low Pressure Turbine Rotor

    pp. 745-750

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    Austenite grains in the core of large scale turbine rotor forgings are refined by repeating annealing treatments afterforging in order to improve the ability of detection of flaw by ultra sonic wave. The treatments, however, require high cost and long time. The grain growth behavior of austenite during holding at high temperature following hot deformation was investigated using hot deformation simulator to achieve refinement in austenite grain by controlling hot forging.
    Austenite grain markedly grew to about 4mm during holding for 5000s at 1250°C after a small amount of deformation of 5% at 1250°C. In the specimens in which extremely large austenite grains were formed, deformed austenite recrystallized statically by bulging mechanism and there were many grain boundaries with unstable triple point in recrystallized austenite before grain growth. On the other hand, only a few grain boundaries with unstable triple point were observed in samples deformed at more than 10%. Since a small strain is applied to forgings at the last stage of forging, it appears extreme grain growth occurs. There is a possibility that extreme grain growth can be prevented by accumulating strain to more than 8%, which can be achieved by forging with a period within 30s between deformations at a certain position.
  • Manufacturing Process of a Forged TiAl Turbine Rotor Containing B2 Phase

    pp. 751-756

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    Manufacturing process of a forged TiAl alloy with a commercial size is investigated in order to realize practicalapplication of TiAl as a turbine rotor material in a high performance and high efficiency turbine engine. Accomplishment of apparently contradicting properties such as good hot deformability and high temperature strength is pursued in a alloy of Ti-45Al-8Nb-2Cr (at%) which contain B2 phase. The phase transformation behavior of this alloy is first investigated during quenching from temperatures between 1473K1673K and the basic scheme for the manufacturing process, e.g. casting→heat treatment in the (γ+B2) phase field→isothermal forging→heat treatment in the phase field which contains α2 (α) phase, is defined. Then various factors such as the heat treatment and forging conditions for the stages up to the isothermal forging are examined by compression tests. Finally, it is shown that manufacturing of a 210mm in diameter 40mm in thickness forged piece can be successfully done using a industrial 6000ton press without causing any plastic deformation of the IN100, die material.
  • Effects of Minor Alloying Elements on Inherent Creep Strength Properties of Ferritic Steels

    pp. 757-762

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    Creep rupture strength properties of carbon steel have been analyzed from a viewpoint of inherent creep strength, andthe effects of minor alloying elements on inherent creep strength have been investigated. Inherent creep strength, which is a new concept proposed by the authors, is an essential strength property independent of both microstructural morphology and time, and the governing factor of long-term creep strength property. Large heat-to-heat variation of inherent creep strength observed for the carbon steel has been cleared to be caused by a remarkable improving effect of Mo on that. However, strengthening effect of Mo has been speculated to saturate at a slight amounts of about 0.03mass%. It has been concluded that an inherent creep strength of ferritic steel is governed by solid solution strengthening effect due to such as C and Mo, and the maximum inherent creep strength is obtained by the addition of C and about 0.03mass% of Mo. Moreover, it has been suggested that the inherent creep strength of many ferritic heat resistant steels are maximum level for ferritic steels, consequently, creep rupture strength of those converges to an almost same level at the long-term region.
  • Change of Microstructure and Toughness during the Long-term Aging of Various Steels for the First Wall Structural Materials of Fusion Reactors

    pp. 763-768

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    Various steels, such as a type 316 austenitic steel, its modified steels, ferritic heat resisting steels and high Mn-Cr austenitic steels have been proposed for their application to the first wall structural component of future fusion reactors and many investigations have been performed concentrating on the heavy irradiation effects of these materials. As a fundamental study, the present authors have investigated the change of microstructure during the long term aging and its effect on the toughness and fracture mode of these materials. Due to the formation of large amounts of coarse carbides within grains and on grain boundaries during the 8000 hours aging, toughness was much deteriorated and intergranular fracture and cleavage fracture were introduced by the impact test at room temperature in these materials.
  • Temperature Dependence of Phosphorus Distribution Ratio between CaO-SiO2-CaF2 Slags and Fe-Cr-C Alloys

    pp. 769-771

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