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

Tetsu-to-Hagané Vol. 83 (1997), No. 2

  • Sulfurization Mechanism of Wustite

    pp. 85-90

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    In order to investigate the mechanisms of sulfurization of iron oxide such as the formation of iron sulfide dust during smelting reduction of iron ore, wustite samples synthesized to some specific compositions as well as magnetite and metallic iron were sulfurized mainly at 900°C in a controlled sulfur partial pressure. The degree of sulfurization reaction was thermogravimetrically monitored for each experiment and several samples were subject to XRD, SEM and EDX analyses. The rate controlling step of sulfurization reaction has been considered to be the diffusion of iron in the FeS layer produced, and its diffusion coefficient at 900°C is estimated to be 4.7-7.0×10-9cm2/s.
  • Stress Analysis of the Packed Bed in Blast Furnace

    pp. 91-96

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    Experimental study using a small scale blast furnace model as well as theoretical study based on the elastic-plastic theory were made to elucidate the characteristics of the stress field formed inside blast furnace and following results were obtained.
    1) The stress distributions both on the furnace wall and on the furnace bottom measured in the experiment agreed approximately with those obtained through the numerical analysis based on the elastic-plastic theory.
    2) The shape of deadman and the vertical distribution of the horizontal stress inside the cold model furnace observed in the experiment also agreed with those obtained through the same analysis.
    3) Followed by the results presented in 1) and 2), the elastic-plastic theory was confirmed to be useful to elucidate the stress field formed inside blast furnace.
  • Development of Evaluation Method for Softening-melting Properties of Sinter

    pp. 97-102

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    In order to clarify the sinter properties desirable for blast furnace operation, a new measuring apparatus with a gas preheater has been developed. This apparatus can raise a gas temperature up to 1700°C and conduct an adiabatic heating control. Using this apparatus, it is possible to detect the heating and reduction delay of sinter due to a rapid endothermic reduction of molten FeO.
    As a result of the experiments by using sinter samples produced by a sintering pot, the sinter having a low bulk density and a large amount of micro pores shows a high reduction degree at 1200°C.
    A new evaluation method has been presented to determine the sinter properties related to the permeability of cohesive layer in the blast furnace. In this method, five indices which need to have values with certain ranges are selected.
    The sinter desirable for blast furnace operation should have a low SiO2 content when CaO/SiO2 is high. This means that a sinter should have a low slag volume with a high melting point in order to form a permeable cohesive layer.
    Further studies are necessary to measure the actual sinter properties and verify the validity of this method by analyzing the relation between these indices and the results of the blast furnace operation.
  • Control Technique of the Melting Reaction in Sintering Process by the Fine Part Selective Granulation of Clayish Iron Ores

    pp. 103-108

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    To control the melting reaction in sintering process by the fine part selective granulation of clayish iron ores, some studies consisted of tablet firing tests, sintering pot tests and an operation test at a commercial sintering machine were carried out. On the basis of these tests, the melting property of the bond-forming part which form the melt for coalescing pseudo-particles, and the heat supply for the melting were investigated.
    It was clarified that the melting property of the bond-forming part can be determined by the tablet's deforming temperature related to CaO and Al2O3 content. Optimum heat supply value corresponding to the melting property of the bond-forming part was recognized for the strength of sinter (SI). As a result, the contour line of SI could be described on the two-dimensional map consisted of the melting property and the heat supply. Furthermore, it was possible to control the operational point on that map by the fine part selective granulation of clayish iron ores.
    From the result of the operation test at a commercial sintering machine, the green pseudo-particles of clayish iron ores by selective granulation was strong enough to retain the segregation of chemical composition and heat source in the raw mix after handling. Also, the increase in melt formation of the sinter products was confirmed by the increase in open pore ratio and pore size. Finally, coke consumption, permeability and reducibility of sinter were significantly improved by the fine part selective granulation of clayish iron ores.
  • Development of a Method for Measuring Sinter Porosity by Applying a Vacuum Packing Technology and Its Application to the Evaluation of Sinter Property

    pp. 109-114

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    PAC method, a new method measuring the porosity with concave in iron are sinter, has been developed by applying a vacuum packing technology. PAC method is applicable to measure the total porosity of porous objects with an irregular shape such as iron are sinter or sinter lump with a size of 10 to 100 mm. Porosity of commercial plant sinter measured by PAC method shows strong relativity to the reducibility ( JIS-RI). Evaluation of total porosity by PAC method suggests directions for controlling the sinter reducibility. Furthermore, change of sinter porosity in handling process is detectable by PAC method. Porosity of sinter lump decreases propotionally to handling times along the process flow from sintering machine to blast furnace. PAC method provides significant data for process analysis and control.
  • The Effect of Crystallization of Mold Powder on the Heat Transfer in Continuous Casting Mold

    pp. 115-120

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    It has been known that one of the primary trouble on the production of middle carbon grade steel is longitudinal cracks on the cast surface, and occurrence frequency of these cracks is effectively reduced with a lower heat flux in a mold. In order to decrease the heat flux in the mold, a mold powder with high crystallization temperature has been ordinarily used. To make clear the mechanism of lowering heat flux in the mold using the mold powder, laboratory experiments were conducted. Thermal resistance was measured using a dipping test of copper mold, which had several thermocouples on the surface. Interfacial thermal resistance was about 2-3 times of thermal resistance of film. To clarify the change of the surface texture by crystallization, the surface of powder plate was observed with a laser microscope. The surface started to wave, when the glass changed to crystal above 830K. Therefore, it is supposed that the wave on the surface of the powder film caused an increase in the interfacial thermal resistance.
  • An Analysis of Temperature, Thermal Stress and Shape Defect during Accelerated Cooling in Steel Plates

    pp. 121-126

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    A mathematical simulator during accelerated cooling after rolling in steel plates has been developed. The simulator can predict simultaneously the temperature, the thermal stress and the shape defect during cooling with taking the phase transformation into account.
    The transverse temperature distributions at the entry of cooling device and at the exit of hot leveller were measured in an actual plate plant, and also the thermal stresses after cooling (the residual stresses) and the cambers after longitudinal cutting were measured. It was confirmed that their values can be predicted by the simulator.
    The residual stresses predicted by the above mentioned simulator was compared with those by a simplified elastic method which requires only the transverse temperature distribution at the exit of hot leveller in calculation. When the transformation is finished in all cross section at the exit of hot leveller, both values are completely coincident. But there is a big difference between the two when the transformation is not occurred in all cross section or is occurred partly at the exit of hot leveller.
  • Structural Variation along Thickness Direction of Extra-low Carbon Sheet Steels Rolled in Ferrite Region

    pp. 127-132

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    The application of an EBSD technique in an SEM reveals a new approach to analyze a structural variation along the thickness direction of extra-low carbon sheet steels rolled in the ferrite region. The fine recrystallized grains in the sheet steel rolled without lubrication are observed near the surface due to a strong additional shear strain between a material and a roll, and those grains are considered to recrystallize dynamically by means of image-quality imaging with EBSD. The nonuniform recrystallization texture through the thickness are formed in the sheet steel rolled without lubrication by means of orientation imaging with EBSD, <110>//ND recrystallized grains being formed near surface, <111> //ND and <100>//ND recrystallized grains being formed at the mid plane. On the other hand, <110>//ND recrystallized grains are not formed preferentially near surface and <111>//ND and <100> //ND recrystallized grains are formed uniformly throughout the thickness in the sheet steel rolled with lubrication. The orientation imaging also reveals the tolerance of <110>//ND recrystallized grains around <110> //ND axis in the sheet steel rolled without lubrication, resulting in the <110>//ND grains with small tolerance being formed at the 1/10 plane from surface and the <110> // ND grains with larger tolerance being formed at the thickness location toward the surface and center from 1/10 plane. The image-quality imaging and orientation imaging allow a more visual and intuitive understanding of the nonuniformity of a microstructure and texture formation in the sheet steel rolled without lubrication than conventional method such as optical microscopy and X-ray diffraction measurements.
  • Investigation on the Manufacturing Conditions of Commercially Pure Titanium Seamless Pipes by the Inclined Rolling Process

    pp. 133-138

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    The manufacturing conditions of commercially pure titanium seamless pipes by inclined rolling process were investigated on laboratory scale. Elevated temperature torsion test was carried out to alpha forged and beta forged billets. Piercing condition was determined by a model piercing mill. A part of pierced shell was hot rolled and annealed to investigate the possibilities to attain equiaxed structure in the products.
    The results were summarized as follows.
    (1)Piercing operation above 1223K is recommendable to avoid low piercing efficiency of the commercially pure titanium, while the material possesses sufficient deformability in beta phase region.
    (2)Equiaxed structure is obtainable by the piercing operation in beta phase region, followed by rolling in alpha phase region and annealing at 1023K. Piercing operation below 1373K is necessary to achieve equiaxed structure.
    (3)Fine grain alpha forged material possesses superior deformability at elevated temperature to coarse grain beta forged material. However, the beta forged material possesses sufficient deformability for the piercing operation in beta phase region.
  • Reaction Diffusion between Carbon Steels and Molten Lead Saturated with Chromium

    pp. 139-144

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    Various kinds of carbon steel specimens containing 0.15-0.8 mass%C were annealed in the molten lead saturated with chromium at 1173 to 1373 K. The formation and growth kinetics of the chromium carbide layer by the reaction diffusion between the specimen and the Pb-Cr melt has been investigated. Four kinds of carbide layers composed of the following structures were formed on the specimen surfaces depending on annealing temperature and the carbon content of the specimen: S/Cr7C3, S/Cr23C6, S/Cr23C6/Cr7C3/Cr23C6 and S/Cr7C3/Cr23C6, where the letter “S” means the steel substrate. These carbide layers contain a large amounts of iron, grow according to the parabolic law and have Vickers hardness of 1700-2000. The method used in this work is applicable to the chromium carbide coating on carbon steels containing more than 0.15 mass%C.
  • Effect of Base Resin Component and Additives on Performance of Organic Composite Coated Steel Sheet with Excellent Lubrication

    pp. 145-150

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    There is an increasing demand for steel sheet that should be completely free from oiling and degreasing during the forming operation in order to improve working environment and hence global environment ; In order to achieve this we studied a lubricated galvanized steel sheet, which has a thin organic film consist of base resin, lubricant and silica for the anti-corrosive agent on the chromated upper layer.
    A lubricated galvanized steel sheet requires not only good lubricity but also good resistance to mechanical damage that causes deterioration of surface appearance. From the point of the improvement of resistance against mechanical damage, an organic film has high level of mechanical strength to reduce powdering by sliding, and has adequate softness that allows the film to follow to the press deformation well. The tensile strength and elongation of various polyurethane resin films were measured. On the basis of the test results, it was concluded that blended aromatic resin base polyurethane and aliphatic one was bridged by hardener has good mechanical properties to provide excellent surface appearance.
    Polyethylene lubricant in the film had good coefficient of friction at wide range of temperature, as compared with other solid lubricant. From the point of the balance of corrosion resistance and surface appearance after forming, 1015wt% silica content in the film had better performance.
  • Development of Estimation Method of Effective Thermal Diffusivity of Composite Materials

    pp. 151-156

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    The estimation method of the effective thermal diffusivity of composite materials by numerical calculation of heat transfer in the composite materials using image data was developed. In this method, time for the numerical calculation was reduced significantly by characterization method of the composite materials. The characterization method of composite materials was applied to original image data as follows: At first, dispersion material and pore were approximated by an ellipse as one component. Next, dispersion material was also approximated by an ellipse. Moreover, frame of matrix material was characterized with thinning method. Finally, these two ellipses and the frame were overlapped each other. In this way, characterized image data were obtained and were used for estimation.
    Characterized image data of Fe-Al2O3 dispersion type composite materials were obtained with this method.
    The effective thermal diffusivity of the sample was also measured by Halogen Flash method. The estimated results agreed well with the observed data. The effective thermal diffusivity was not affected by the particle size distribution of dispersion material but by existence of pore.
  • Iron-based Element for Low Temperature Thermoelectric Generator

    pp. 157-161

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    Direct conversion of low temperature waste heat source into electrical energy with thermoelements is an interesting and challenging problem. In this study, the thermocouple consisting of a junction between Fe and Fe-712mass%Al alloy has been developed. The uni-couple exhibits the power of 40μV/K at room temperature which is equivalent to that for the junction between Cu and Constantant. The iron and iron-aluminum alloy may be of great significance as materials for low temperature thermoelectric energy conversion because of their abundant production.
    Cold-roll formed steel sheets were used for trial manufacture of a generator with a series connection of thermoelectric elements. The steel sheet was bent in sharp waves, wrapped with aluminum foils tightly on the reciprocal planes of the waves and heat-treated for alloying by diffusion of aluminum into the steel matrix.
    Electric power generating facility using the iron and iron-based devices may have definite advantages : It has no moving parts and requires very little attention. It cannot wear out. Therefore, the determining factor of the possible use of thermoelectric generator is its efficiency. So, the latter half of this paper has been focused on the possibility to convert low temperature heat source into useful power with high efficiency. Recovery of electricity was discussed on the basis of a thermoelectric generator of the heat exchanger type in which the heat transferred by conduction through a energy panel consisted of a series of thermoelectric elements is accumulated in the air circulating as coolant and recycled as a heat source for the use to a subsequent thermoelectric panel.
  • Effects on Business Efficiency of Application of Information and Telecommunication Technology to Major Steel Companies

    pp. 162-167

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    This research is aimed to estimate the present situation of introduction of information and telecommunication technology by Japanese major steel companies and make clear its more useful ways in the future with the analytic hierarchy process called AHP method. Furthermore, we made the similar survey on a chemical company and several governmental institutes to compare with the results on the steel companies. As far as our investigation is concerned, the steel companies have been found to be yet fairly behind the said other organizations compared in terms of introduction of the information and telecommunication technology into their business activities and have more possible areas to be targeted upon to improve their business efficiency.

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