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

Tetsu-to-Hagané Vol. 96 (2010), No. 8

  • Viscosity of Iron Oxides Containing Multicomponent Slags

    pp. 469-474

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    DOI:10.2355/tetsutohagane.96.469

    Viscosity of the multicomponent slags which contain iron oxides (FeO and Fe2O3) have been measured by using rotating crucible method. In our experiments, we measured the viscosity from 1673 to 1873K under air. Effects of the basicity and the iron oxide additions on the viscosity were clarified.
    Temperature dependences of the viscosity for the slags were expressed by Arrhenius type equation in the present study. The viscosity of the slags decreased linearly with increasing the basicity (CaO/SiO2). Also, the viscosity of the slags decreased with increasing the additive content of iron oxides. The decreases in viscosity with the addition of iron oxides are larger in the lower basicity system than those in the higher basicity system. The results of chemical analysis for the slag samples after viscosity measurements indicated that iron oxide in these slags has mainly existed as Fe2O3 (Fe3+). Therefore, we calculated the parameter of αFe2O3 which was a coefficient related to the amphoteric behavior of Fe2O3 in accordance with the Iida's model. The parameter of αFe2O3 increased with decreasing the bacisity. The results suggested that Fe2O3 had a greater tendency to behave as a basic oxide in the lower bacisity system than in the higher basicity system. It is therefore that the decreases in viscosity with addition of the iron oxides are considered to be large in lower basicity system.
  • Effect of Carbon Structure Crystallinity on Initial Stage of Iron Carburization

    pp. 475-481

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    DOI:10.2355/tetsutohagane.96.475

    Iron carburization is one of the most important reactions in iron making process. If the rate and efficiency of carburization reaction are increased, energy consumption of the process will be reduced to a large extent. The purpose of this study is to clarify the effect of carbon structure on initial iron carburization behavior for suggestion of effective carbon utilization in iron making process. Samples of different carbon structures were prepared by heat treatment of CH4 decomposed carbon at various temperatures. Carbon structures of prepared carbon samples were analyzed by a Raman spectroscopy. For experiments, high-purity iron samples directly-contacted with carbon were prepared. A laser microscope combined with an infrared image furnace was used for heating of the sample and “in-situ” observation of carburization phenomena. Carbon concentration profile in iron sample was analyzed by a wavelength dispersion type electron probe micro analyzer. The results of this work showed that primary Fe–C liquid formation temperature became lower from 1439 to 1431K with use of lower crystallization carbon. It was indicated that utilization of the lower crystallization degree of carbon structure causes formation of primary Fe–C liquid at the lower temperature.
  • Formation Mechanism of Spheroidal Graphite in Nickel Alloy Cooled Ultra-Rapidly

    pp. 482-491

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    DOI:10.2355/tetsutohagane.96.482

    The formation mechanism of spheroidal graphite (S.G.) in high purity Ni–C and Ni–C–Mg alloys cooled ultra-rapidly from the liquid state at four different rates (Exp. 1–Exp. 4) was investigated. The cooling rate increased from 2×104 to 5×105 (K/s) in the order of the experimental number. Contrary to the previous result on S.G. in Ni–C alloy with impurities, no core of the different phase was found at each center of S.G. (1–3 μm in dia.) in Ni–C alloy in Exp. 1 and a number of the S.G. appeared to have collapsed or burst during the process of growing. In Ni–C–Mg alloy samples of Exp. 1 and Exp. 2, the S.G. with various sizes (1–10 μm in dia.) were observed; some had hallow in each center and some appeared to have collapsed or burst. In Ni–C samples of Exp. 2, Exp. 3 and Exp. 4, and Ni–C–Mg samples of Exp. 3 and Exp. 4, only a few S.G. was found.
    The results could provide two growing mechanisms of the S.G., namely, a heterogeneous nucleation of graphite on a core of the impurity phase formed during cooling, and a nucleation of graphite on the interface between a gas bubble and supercooled liquid nickel. The gas bubble came from vaporized Mg or Ar atmosphere; the Ar gas had been contained in porous alloy sample made of powder of Ni and graphite by pressing. At high cooling rate, the increase or decrease in gas pressure in the bubble would cause the collapse and burst, thus results in a few S.G.
  • Investigation of Scale Behaviour during Hot Steel Rolling by Oxide Glass

    pp. 492-497

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    DOI:10.2355/tetsutohagane.96.492

    In hot rolling process, scale is formed on steel surface by oxidation at high temperature. As the scale influences the friction between roll and workpiece, the scale affects rolling characteristics significantly. The influence has not been understood sufficiently due to experimental difficulties. The authors proposed to use glass powder to observe the scale as hot rolled. The pickled cold mild steel sheet was inserted to a furnace at hot rolling temperature (1273K) filled with argon. After 600 s, the atmosphere was changed from argon to air to allow oxide scale to grow for 0, 10, 40 s. After the oxidation, the sheet was rolled immediately on a two-high laboratory rolling mill. The thickness was reduced from 10 to 40%. After passing the roll bite, glass powder was sprinkled over the sheet. Scanning electron microscopy on the longitudional section revealed that the scale deformation is relatively uniform if the reduction is lower than 20%. If the reduction is higher than 30%, matrix steel is extruded through cracks in the scale to the outermost surfaces.
  • Microstructure and Bond Strength of Steels Using Low-Cr-Substituted Cementite Foil

    pp. 498-503

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    DOI:10.2355/tetsutohagane.96.498

    In the preceding paper, the eutectic liquid that appears between cementite (θ) foil and austenite has been proposed the most suitable for rapid transient-liquid-phase (TLP) bonding of steels. A partial substitution with Cr was required for metastable θ to be thermodynamically stable up to solidus temperature. On the other hand, the liquid region disappeared quickly by C diffusion and results in a severe Cr segregation at bonded interface. This work aims to decrease the ratio of Cr substitution in θ so as to eliminate a time for homogenization and to allow the use of as-bonded steel parts. The synthesized θ with 1 mass% of Cr (1Cr-θ) showed an enhanced tendency of decomposition on cooling from 1373K. However, the 1Cr-θ filler has been confirmed to give the eutectic liquid that dissolved V during TLP bonding of V-microalloyed steels. After holding for 180 s at 1453K, a gradient ferrite–pearlite microstructure has been attained in the bond without any boundaries or intermediate phases. The bonded steel showed a tensile strength and elongation corresponding to the original V-steel.
  • Volume of Sedimentary Particles Lifted up by a Swirl Motion of Bubbling Jet

    pp. 504-510

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    DOI:10.2355/tetsutohagane.96.504

    In our previous research, we mentioned about mixing of small solid sedimentary particles using a swirl motion of a bubbling jet. The lifting behaviors of the particles were classified into two types depending on the aspect ratio (LN/D) of the bath, where LN the nozzle depth and D the bath diameter. The two types of lifting behaviors were closely associated with the isolated vortex appearing for LN/D=0.2–0.4 and twin vortices appearing for LN/D=0.5–0.8. These vortices were similar to the tornado. In this study, empirical equations are proposed for the volume of sedimentary particles lifted up by a swirl motion of a bubbling jet as functions of the gas flow rate, vessel diameter, bath depth, and the physical properties of fluids.
  • Hydrogen Production by Using Redox Cycle Reaction of Foreign Oxide Coated Iron Oxide

    pp. 511-516

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    DOI:10.2355/tetsutohagane.96.511

    The hydrogen energy society is desirable to mitigate global warming. The redox cycle reaction of iron oxide Fe3O4 which can generate 4.8 mass% hydrogen is considered as one of means to storage and supply it. However, this reaction is known to be significantly retarded due to sintering iron oxide or iron particles. In this work, influence of foreign oxides coating on the surface of iron oxide fines is examined to improve the reaction efficiency.
    Al2O3 coating enhanced the reaction efficiency until 97% even for more redox reaction cycles which is superior to SiO2 coating, probably because of difference of gas diffusivity through coating layers.
    Redox reaction rates in this work were nearly one order of magnitude larger than previous ones, which were obtained with samples prepared by coprecipitation from solution containing additives.
    The activation energy for reduction of Al2O3 coating samples was obtained 41.2 kJ/mol close to that in a literature.
  • Estimation of Steel Stock in Building and Civil Construction by Satellite Images

    pp. 517-523

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    DOI:10.2355/tetsutohagane.96.517

    Steel is the most widely used material in the world. Many studies related to material flow analysis of steels have been conducted for Japan, Asian countries and the world. Top-down and bottom-up approaches were used in these material flow analyses and stock accounting. However, applicability of these approaches is quite dependent on data availabilities. To overcome this problem, we proposed a methodology to estimate steel stock based on satellite images. Previous studies told us that night time light images collected by satellites have strong correlation with human activities, e.g. electricity consumption, CO2 emissions, GDP, etc., which also links to the amount of steel stock. In this study, night time light image was used along with land cover data to estimate the building and civil construction steel stock in Japan and Asian countries. Analysis was first performed within Japan for each prefecture, and then the result was applied countrywide for Japan, China, South Korea and Taiwan. It was found that the building steel stock showed high relativity with urban night time light while civil construction steel stock was better described by total night time light.
  • Refining of High Quality Steels Using CaO–Al2O3–MgO Flux in the Combination Processes of EAF–LF–RH

    pp. 524-529

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    DOI:10.2355/tetsutohagane.96.524

    The new flux of CaO–Al2O3–MgO system was developed for the refining of low impurity and high quality steel from steel scrap or reduced iron by the combination of EAF–LF–RH. The practical tests of 12 heats using 110 ton scale EAF were carried out at 1873K. The chemical composition of final products was [mass ppm S]=40–60, [mass ppm O]=2–5 and [mass ppm N]=50–70 without special troubles like the damage of refractory materials.

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