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

Tetsu-to-Hagané Vol. 83 (1997), No. 9

  • Thermal Analyses of the Sintering Reactions of Iron Ores

    pp. 539-544

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    Sintering phenomena of iron ores have been examined by applying several methods of thermal analyses, i.e., thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). Particular focus was given on the assimilation and melting behavior of major raw materials.
    For the reaction between fine iron ores and limestone, heat of initial melting has a negative relation with SiO2 content of the ore. Mineral state of Al2O3 component influences the melting temperature of the mixture, possibly through the stabilization of calcium ferrite phase formed during heating. However, that of MgO component does not have much effect on the melting behavior. Increase in particle size of are gives remarkable effect in promoting initial melting when using ores having relatively high gangue minerals at a lower total CaO concentration. In contrast, increase in limestone size tends to suppress.initial melting at higher total CaO concentration. Reaction between melt and coarse iron are particles proceeds from lower temperature when using pisolitic ores while are having high iron content slowly dissolves at higher temperature. Reactivity of dolomite with melt is larger than serpentine and promotes formation of initial melting.
  • Combustion and Gaification Reaction Behaviors of Plastic in Blast Furnace

    pp. 545-550

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    In order to establish the plastic injection technology in the blast furnace, the behaviors of plastic pyrolysis, combustion and gasification reaction have been investigated with two kinds of model experiment; one is the vertical tower type reactor called the combustion model and the other is the blast furnace type reactor called the hot model.
    The combustion of plastic does not occur in the blast having the temperature of 1250°C and the O2 enrichment of 0% in the blowpipe and tuyere. The combustion starts in the air over the temperature of 1550°C, but the CO2 gasification does not occur at this temperature in the combustion model.
    The split of plastic occurrs in the atmosphere over the temperature of 2000°C in the raceway from 10002000μm to 200μm. The split plastic is burnt in the raceway, the unburnt plastic is consumed and accumulated in the hot model and it does not flow out of the top.
    The entering of plastic contained fines into the deadman can be suppressed by injecting the plastic directly into the raceway through the tuyere or by keeping the distance of the lance tip from the tuyere nose as short as possible in case of the injection through the side of blowpipe.
    The plastic injection alone is better than the mixing injection with pulverized coal in order to maintain the permeability in the lower part of the hot model.
  • The Inflow to a Deadman of Fine Coke Generated near the Lower Part of the Shaft in a Blast Furnace

    pp. 551-556

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    In order to clarify the descending behavior of fine coke generated near the lower part of the shaft in a blast furnace, the fundamental experiment using a two dimensional cold model simulating the blast furnace was carried out. The results are as follows.
    Most of fine coke generated near the central part at the radial axis flows to the raceway and part of fine coke percolates at the slope of the deadman. The percolation to the deadman of fine coke was influenced by Dfine/Dlump, Vt/Vh, and gas velocity in the deadman. Where Dfine and Dlump are an average size of fine coke and lump coke in the deadman respectively, Vt is a descending speed of coke at the throat and Vh, is a renewal speed of deadman. In case of the low gas velocity, the smaller Dfine/Dlump is and the larger Vt/Vh is, the higher ratio of fine coke in the deadman is. In case of the high gas velocity, the fine coke does not percolate to the deadman.
  • Effect of Cr, P and Ti on Density and Solidification Shrinkage of Iron

    pp. 557-562

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    Densities from room temperature up to 1650°C of pure iron and ferroalloys containing Cr, P and Ti were measured by a sessile drop method. Based on the results, effects of Cr, P and Ti on solidification shrinkage were made clear. Accuracy of the present results was evaluated compared with previous studies. Change in shrinkage during solidification due to microsegregation was also discussed.
  • Effect of P and Ti on Surface Tension of Molten Iron and Entrapment of Inclusion by Liquid/Solid Interface in Molten Steel

    pp. 563-568

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    Surface tension of molten iron and molten ferroalloys was measured by a sessile drop method in order to make clear the effect of P and Ti on surface tension of liquid iron in the concentration range of less than 1 mass%. Based on the present results, effect of P, Ti, Mn and C on entrapment of alumina inclusion in a solidified shell was discussed, taking account of gradient of boundary tension between alumina inclusion and molten iron in a boundary layer at a solidification front.
  • Effect of the Chemical Composition and Double-cold-reducing on the DI Canmaking Properties

    pp. 569-574

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    The DI (Drawn and Ironed) canmaking properties (the effect of the load of DI canmaking, the dome inversion pressure and the load of neck forming) was measured in the 350ml 211 (66mm) diameter size DI canmaking with many kinds of steels prepared in the laboratory. The chemical composition, especially carbon content, was widely varied from 0.05 to 0.0010wt%. The following points were clarified.
    1) The DR (double-cold-reduced) ultra-low carbon steel tinplate is advantageous for preventing the wrinkles at the necking by reducing the strength of the expected necking part.
    2) The bottom reverse pressure depends on both thickness and YS of the tinplate. The pressure increment is evaluated experimentally to be 0.074MPa/0.02mm in thickness and 1.7MPa/10MPa in YS, respectively. As the results, the application of the-ultra-low carbon steel, adequately hardened by the cold reducing after annealing, may be advantageous for reducing tinplate thickness without deterioration of necking formability.
  • Effect of Nitrogen Distribution on Pitting Corrosion Resistance in High Power LASER Welded Duplex Stainless Steels

    pp. 575-580

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    Microstructural features and pitting corrosion properties of duplex stainless steel weld metal have been studied by means of 25kW CO2 LASER welding process without filler metals from viewpoints of nitrogen distribution and nitrides precipitation. Two types of pitting mechanisms have been clarified depending upon the cooling rate of the weld metal.
    One is the local nitrogen depletion in the ferrite phase, where pitting occurred, due to the migration of nitrogen from ferrite to austenite when the cooling rate was higher. Pitting resistance was improved by supersaturated nitrogen in the ferrite phase when the cooling rate was extremely high. These behaviors could be explained by the calculation based on nitrogen diffusion.
    The other is Cr depletion due to chromium nitrides precipitation in the ferrite phase when the cooling rate was not so high. The composition was Cr2N, which lowered the pitting corrosion resistance, although CrN precipitated when the cooling rate was higher, which did not affect the pitting corrosion resistance.
  • Pearlite Transformation in High Carbon Steels Deformed in Metastable Austenite Region

    pp. 581-586

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    The effect of deformation in the metastable austenite region on the subsequent transformation in high carbon steels (0.701.09%C) at 948848K has been investigated.
    The size of pearlite colonies is reduced 14 to 7μm in diameter depending upon the degree of deformation from 0 to 60% in the reduction of height of a cylindrical specimen. The deformation induces also the formation of proeutectoid phases (α, or θ) in off-eutectoid steels, and the proeutectoid α, was detected in, for instance, 0.92 mass%C steel transformed at 898K. This result reveals that the eutectoid composition at 898K is higher than 0.92 mass%C.
    The eutectoid point below A1 temperature has been calculated from the balance equation, fα·ΔGα=fθ·ΔGθ, where ΔGα, ΔGθ are the driving force for α and θper mole, and fα, fθ are the mole fractions ofα and θ in the pearlite. The results of the calculation are in good agreement with the experimental data, exhibiting the eutectoid composition at lower temperature is fairly higher than that of the equilibrium diagram (0.8mass%C).
  • Effect of Retained Austenite on the Hydrogen Permeation Behavior in High Strength Steels

    pp. 587-592

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    The permeation behaviors of hydrogen in high strength steels with and without retained austenite were studied by means of electrochemical method. The diffusivity obtained from the permeation curves was smaller and activation energy was larger in steels with retained austenite than those without retained austenite. The hydrogen permeation curves in steels without retained austenite agreed well with theoretical permeation curves, obtained from the assumption of diffusion in homogeneous steel. However, the permeation behavior of hydrogen in steels with retained austenite consisted of two permeation curves. The first curve indicated the permeation in ferrite phase and the second one was that in ferrite and austenite phases or ferrite/austenite interfaces. The apparent diffusivities decreased with the amount of retained austenite but the diffusivities in the first stage agreed well with those without retained austenite in the similar strength steel.
  • Lowering of the Yield Ratio in Solution Hardened Interstitial-free Steel by Employing Transformation Microstructure

    pp. 593-598

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    The employment of the transformation structure by the (α+γ) intercritical annealing was investigated for achieving advantageous decrement of yield ratio (yield strength/tensile strength) in TS 440MPa grade extra low carbon IF steel with the solution hardening by preferential P addition. The transformed microstructure obtained from dual phase annealing induced remarkable low yield ratio even in the high P-added steel (0.10%P-1.5%Mn-0.5%Si). This phenomena, associated with decrease of yield point elongation of as-annealed steel is attributable to the formation of the low temperature transformed phase, which is classified as the granular bainitic ferrite (αB) or bainitic ferrite (αOB) with high dislocation density. It can induce the much movable dislocation in ferrite matrix around the second phase. Low yield ratio was obtained even in the high Mn steel (0.04%P-2.2%Mn-0.4%Si). However, progress of γ transformation exhibited considerable increase of both yield and tensile strengths predominantly, which is caused by extremely high distribution of Mn in γ phase. Addition of B also affects the yielding behavior in the intercritically annealed steel. This can be explained by the contribution of B addition on the Mneq. formula.
  • Room-temperature Stress Relaxation in a Ti-Fe-O Alloy

    pp. 599-604

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    Stress relaxation behavior of a Ti-Fe-O alloy was investigated at room temperature, varying pre-strain level and pre-strain rate. The relaxation behavior is independent of pre-strain. And the stress relaxation rate decreases with relaxation time. At the early stage of relaxation, 0 to 200s, the stress relaxation rate increases with pre-strain rate. However, after 200s, it does not depend on pre-strain rate as dσ/dt=-19.6t-1, where dσ/dt and t are stress relaxation rate and relaxation time, respectively.

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