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

Tetsu-to-Hagané Vol. 95 (2009), No. 12

  • Viscosity Evaluation of Multi-phases Flux by Rotating Cylinder Method

    pp. 807-812

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    DOI:10.2355/tetsutohagane.95.807

    Viscosity of multi-phases fluids, suspensions of spherical polyethylene beads dispersed in silicone oils, has been measured by rotating cylinder method. Results were obtained as functions of the volume fraction and the average particle size of dispersed beads, the viscosity of silicone oil and shear rate at the surface of rotating spindle. In addition, the rheological characterization of the multi-phase fluids was examined from the relationship between the shear rate and the shear stress calculated on the basis of experimental conditions and the viscosity data.
    The apparent viscosities of the multi-phases fluids were found to increase exponentially with increasing the volume fraction of polyethylene beads. Moreover, in the case of the volume fraction of beads were higher than 0.3, the viscosity of these fluids decreased with increasing the shear rate. The relationships between shear stress and shear rate indicated that the highly concentrated fluids with the beads (the volume fraction of the beads were higher than 0.3) behaved as non-Newtonian fluids that were categorized as Bingham fluid.
  • Reaction Behavior of Formed Iron Coke and Its Effect of Decreasing Thermal Reserve Zone Temperature in Blast Furnace

    pp. 813-820

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    DOI:10.2355/tetsutohagane.95.813

    Usage of highly reactive coke in order to decrease thermal reserve zone temperature in blast furnace is considered promising to increase reaction efficiency in blast furnace and to decrease reducing agent rate. We focused attention on the catalytic effect of iron and succeeded in producing highly reactive formed iron coke with high iron content. In this paper the reaction behavior of formed iron coke when mixed with conventional coke and in the presence of alkali was investigated and the following results were obtained. It was shown that when the mixture of iron coke and conventional coke is heated in a reaction gas, iron coke selectively and preferentially reacts near the thermal reserve zone temperature (900°C), which causes a decrease in thermal reserve zone temperature, while conventional coke reacts little and is protected from degradation. It was also confirmed that catalytic activity of Fe and that of K is independent each other and that in the presence of alkali, the reaction beginning temperature of iron coke is lower than that of conventional coke. These results show that the use of formed iron coke could decrease thermal reserve zone temperature in an actual blast furnace where coke reactivity is promoted by condensed alkali vapor.
  • Carburization Degree of Iron Nugget Produced by Rapid Heating of Powderly Iron, Iron Oxide in Slag and Carbon Mixture

    pp. 821-826

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    DOI:10.2355/tetsutohagane.95.821

    Iron nugget making process by rapid heating reduction of powdery iron ore and pulverized coal mixture is regarded as one of the novel iron-making processes. Iron carburization during smelting reduction is especially important reaction step from the viewpoint of saving energy in this process. If the rate and efficiency of carburization reaction are increased, energy consumption of the process will be reduced to large extent. The purpose of this study is to clarify the carburization degree of iron nugget during smelting reduction of the mixture.
    The sample was prepared from graphite, electrolytic iron powder and synthetic slag containing iron oxide to simulate iron carburization phenomena during smelting reduction of the mixture in the present work. The sample was quenched immediately after the mixture changed into nugget shape in a rapid heating process. Laser microscope combined with infrared image furnace was used for sample heating and observation of carburization phenomena, and carbon content in the nugget was chemically analyzed after quenching.
    From above-mentioned investigations, it was revealed that the occurrence of carburization during smelting reduction in the sample mixture is advantageous to obtain higher carbon contain iron nugget.
  • Prediction of Nonmetallic Inclusion Formation in Fe–40mass%Ni–5mass%Cr Alloy Production Process

    pp. 827-836

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    DOI:10.2355/tetsutohagane.95.827

    Thermodynamic consideration is an effective procedure for calculation of inclusion composition prediction. In general, Henrian standard state is used, and the activity coefficients of the constituents are represented by Wagner's formalism in thermodynamic calculations. This formalism is commonly used in low alloy steel, and this is not recommended for high alloy steel. High alloy steel is detailed thermodynamically using the Raoultian standard state, and the activity coefficients of the constituents are converted by Miki and Hino's formalism in this study. The equilibrium relation between Al2O3, MgO, spinel (MgO·Al2O3) and dissolved Al, Mg and O in Fe–40mass%Ni–5mass%Cr alloy (Spacer Frame for fluorescent display) were discussed. Plant data of Fe–40mass%Ni–5mass%Cr alloy were compared thermodynamically with the calculated results. It was found that Wagner's formalism can't be useful for inclusion composition prediction of Fe–40mass%Ni–5mass%Cr alloy, Miki and Hino's formalism should be utilized for high alloy steel.
  • Dispersion Behavior of Low-density Particles and Water Flow in a Bath under Offset Agitation with an Immersion Cylinder

    pp. 837-843

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    DOI:10.2355/tetsutohagane.95.837

    Particle image velocimetry measurements have been carried out to understand the characteristics of fluid flow containing low-density particles in a bath under mechanical offset agitation with an immersion cylinder. The particles disperse deeply and widely in the bath under this agitation method. The water flow pattern does not change drastically with the immersion cylinder. The tip of the vortex tube however shifts from the center of the rotation axis of the impeller to the tip of the impeller blade. The dispersion of low-density particles is highly enhanced by this vortex tip shift.
  • Analysis of Solidified Structure Constituted with Dendrites by Using Solid Analytical Geometry

    pp. 844-850

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    DOI:10.2355/tetsutohagane.95.844

    Solidified structure near the chill zone is complex, since the growth directions of dendrites are not in accordance with the observed plane. Many lines, which are called ghost lines, can be observed in the solidified structure. The ghost lines have been analyzed applying the solid analytical geometry. Dendrite of cubic metals has been simplified with rod as a dendrite trunk and four plates with the same thickness. In order to characterize the solidified pattern, angles of ghost lines (η and ξ) are chosen and calculated using θ, φ and β, which are the important parameters to indicate the dendrite orientation in the space. The calculated results have been confirmed by the experimental results solidified unidirectionally of Al–20mass%Cu alloy. It has been found that the spacing or thickness of ghost lines may be the useful parameters to characterize the spatial array of dendrites with respect to the plane for observation.
  • Determination of Orientation of Dendrite from Solidified Structure Observed in 2-D

    pp. 851-857

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    DOI:10.2355/tetsutohagane.95.851

    Solidified structure near the ingot surface is complex and it is difficult to analyze the crystallographic orientation by the solidified structure. The reason of complexity is that the growth direction of dendrite does not agree with the plane for observation. Thus thick lines called ghost lines are often observed. The ghost lines have been characterized in this study.
    Simplifying the shape of dendrite, the ratio of widths of ghost lines (=γ) has been formulated and the change of γ in orientation of dendrite have been analyzed. It has been found that the angles of ghost lines (η and ξ) as well as γ are the important factors to characterize the solidified structure. In order to determine the spatial orientation of dendrite (θ, φ and β) from η, ξ and γ, the computer program had been developed. Applying this computation method, the solidified structure has been compared with the cross sections of dendrite model. The cross sections obtained by 3D-CAD agreed quite well to the real solidified pattern.
  • Model Analysis on the Effect of Array and Shape of Dendrites on Apparent Pattern of Solidified Structure

    pp. 858-863

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    DOI:10.2355/tetsutohagane.95.858

    It has been found that 3D-CAD is a powerful tool for analyzing the apparent pattern of solidification structure. Using 3D-CAD, the apparent patterns of model dendrites have been analyzed in this study. The effect of distribution of dendrites and the morphology of secondary dendrite arms on the apparent pattern have been investigated. As far as secondary dendrite arms form, it has been found that it can be recognized the ghost lines and it is possible to measure the characteristic parameters of ghost lines, η, ξ and γ, which are defined previously. Therefore, we can analyze the spatial relation of dendrite using these characteristic parameters of ghost lines. On the other hand, when the solidified structures are constituted by cells, which have no secondary arms, ellipses stand in a row on the cross section. Therefore, one could recognize the apparent pattern. However, it is not possible to analyze the spatial relation of the cell, since the ghost lines cannot be specified because of the distribution of cells.
  • Analysis of Valence for Chromate Conversion Coatings Using Laboratory XAFS Spectrometer and a Comparison with X-ray Photoelectron Spectroscopy

    pp. 864-869

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    DOI:10.2355/tetsutohagane.95.864

    We performed a nondestructive and in laboratory evaluation technique of hexavalent chromium (Cr(VI)) in chromate conversion coatings using a laboratory X-ray absorption fine structure (XAFS) spectrometer equipped with W anode X-ray tube. The recorded XANES spectrum of a chromate conversion coating sample with fluorescence mode possessed the Cr–K X-ray absorption edge. We have obtained calibration curves of the ratio of Cr(VI)/Cr(III) by the height of pre-edge peak and the Cr–K X-ray absorption edge energy of the reference samples prepared by Cr2O3 (Cr(III)) and CrO3 (Cr(VI)) particle reagents. The calibration curves showed the high correlation coefficients such as 1.00 for the height of pre-edge peak and 0.99 for the value of the energy on the Cr–K X-ray absorption edge. The ratio of Cr(VI)/Cr(III) in the chromate conversion coating has also been evaluated by the X-ray photoelectron spectroscopy (XPS) and 1,5-diphenyl-carbazide absorption spectrometry (DPC) methods. The ratio of Cr(VI)/Cr(III) evaluated by the laboratory XAFS spectrometer was almost identical to that by XPS method.
  • A New Inclusion Rating Method by the Tensile Test with Hydrogen-precharged Specimens

    pp. 870-879

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    DOI:10.2355/tetsutohagane.95.870

    A new inclusion rating method by the tensile test with the hydrogen-precharged specimens is proposed. The method is essentially based on the statistic extremes method of inclusion rating in which the maximum inclusion is found by the simple tensile test with the hydrogen-precharged specimens. In order to verify the validity of the new inclusion rating method, that is the tensile test method with the hydrogen-precharged specimens, tensile tests and fatigue tests were carried out for bearing steel (JIS-SUJ2, Vickers hardness HV=682, 611, 559, 447, 346) and the inclusions appeared on the fracture surface were investigated. It was confirmed that the distribution of extreme values of Al2O3·(CaO)X inclusions obtained by the tensile test method with the hydrogen-precharged specimens coincided with that obtained by the fatigue test method. On the other hand, the distribution of extreme values of inclusions obtained by the optical microscope method was different from those obtained by the tensile test method with the hydrogen-precharged specimens or fatigue method. The inclusion rating method by the fatigue test can be replaced by the tensile test method with hydrogen-precharged specimens. The proposed method is more convenient and reliable than other existing inclusion rating methods.
  • Variation of Cleavage Trigger Morphology in Low Carbon Steel, Depending on Stress Condition

    pp. 880-886

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    DOI:10.2355/tetsutohagane.95.880

    Fracture toughness of low carbon steel is one of the important properties to assure the integrity of steel structure. However, it is well known that fracture toughness is sensitive to many factors; materials factors such as microstructure, loading conditions such as loading rate and temperature, mechanical factors such as plate thickness and plastic constraint. The local fracture criterion approach is helpful to estimate the effect of some factors above on fracture toughness. When we evaluate the temperature effect and/or the constraint effect on fracture toughness using the local fracture criterion approach, the same fracture mechanism should be assured in the variation of temperature and/or plastic constraint. Cleavage facet and river pattern on the fracture surface generally suggest the cleavage type of fracture. However, cleavage trigger mechanism is rather important because an onset of unstable crack propagation along cleavage plane is generally the bottleneck process of brittle fracture. It should be well examined whether cleavage trigger mechanism is kept constant independent of temperature and plastic constraint for the applicability of the local fracture criterion approach. In the present work, the morphologies of cleavage triggers, which appeared at different temperatures and constraint, were examined. The variation of cleavage trigger morphology was also discussed referring to the local stress and strain condition.
  • Evaluation of Hydrogen Embrittlement for High Strength Steel Sheets

    pp. 887-894

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    DOI:10.2355/tetsutohagane.95.887

    The risk of delayed fracture should be evaluated when applying ultra high strength steel sheets to automotive parts. Steel sheets for automobiles are usually formed into various parts by cold working. Therefore, plastic strain introduced by the cold working must be considered as a factor affecting the hydrogen embrittlement in addition to the applied stress and the content of diffusible hydrogen entered into steels, which are considered as factors affecting the hydrogen embrittlement of high strength steel bolts. In this study, the influence of plastic strain, as well as stress and diffusible hydrogen content, on hydrogen embrittlement of steel sheets was quantitatively studied by using an 1180 MPa grade cold rolled steel sheet. Plastic strain was introduced by U-shape bending. Stress was applied by tightening the bent specimen with a bolt. Then, hydrogen was introduced by immersing in hydrochloric acid. The time to fracture and the content of diffusible hydrogen entered into steel were investigated. The fracture was promoted by severe deformation, and it seemed to be caused by the presence of micro cracks and/or micro voids. The hydrogen cracking conditions region of the steel sheet was mapped in the three-dimensional space with the axes of applied strain, applied stress and diffusible hydrogen content. It was considered that the evaluation of the risk of delayed fracture of automotive parts made of the steel sheet under service environment was possible by a comparison of the hydrogen cracking conditions and the service conditions of the parts on the 3D space.
  • Mixing of Small Solid Particles Using a Swirl Motion of a Bubbling Jet in a Cylindrical Vessel

    pp. 895-901

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    DOI:10.2355/tetsutohagane.95.895

    When air is injected vertically upwards into a water-filled cylindrical vessel through a J-shaped lance, two types of swirl motions of the water in the vessel appear under specific conditions: shallow-water wave type and deep-water wave type. The swirl motions are similar to the rotary slashing. The deep-water wave type of swirl motion has high mixing ability. Small solid particles placed on the bottom of the cylindrical vessel can be lifted up into the bath through an effect of the swirl motion. The lifting behaviors of the particles can be classified into two types depending on the aspect ratio of the bath.
  • Estimation of Future Steel Stock and Flow in East Asia

    pp. 902-910

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    DOI:10.2355/tetsutohagane.95.902

    A model to estimate future steel stock and demand was developed under the assumption that the steel stock per capita saturates following a sigmoid curve for Japan, China, South Korea and Taiwan. Per capita GDP was used as the variable. Different sigmoid curves were assumed for each end-use, i.e. buildings, infrastructure and automobiles. As in a previous study on automobiles ownership forecast, country-specific saturation values were introduced for steel use in buildings and infrastructure. As an indicator of regional difference, net population density was introduced. The relation between the saturation value and net population density was examined using the Japanese prefectures as samples, and the relation was applied to the East Asian countries. Future population and GDP were substituted into the sigmoid curves and the steel stock and demand was estimated up to 2050. As a result, steel demand for buildings and infrastructure was estimated to reach its peak around 2020 in China, the amount approximately being 330 million tons and 200 million tons respectively. Steel demand for automobiles in China was estimated to continuously increase until 2050 exceeding 100 million tons.
  • Elemental Analysis of Iron and Steel by Solid-phase Extraction/ICP-MS Using a Cation Exchange Extraction Disk

    pp. 911-914

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    DOI:10.2355/tetsutohagane.95.911

    A simple pretreating method which consists of solid phase extraction using cation exchange extraction disk was tried for the determination of trace elements in iron and steel samples by means of inductively coupled plasma mass spectrometry (ICP-MS). The sample of 0.100 g was dissolved by nitric acid, subsequently adding 8 cm3 of 10w/v% ethylenediaminetetraacetic acid disodium salt (EDTA) solution as masking agent for the iron matrix. The sample solution was adjusted by the dilution with water to pH 1.8 or more and poured into the extraction disk. The target elements retained in the extraction disk were then eluted using 10 cm3 of 3 kmol/m3 nitric acid. Quantities of the obtained target elements were determined using ICP-MS. Highly sensitive quantification was established for 6 trace elements in iron and steel, and for Ca, Mn, Mg, Ba, Tl and Sr with the following detection limits [3σ; ng/g (ppb)]: Ca: 4.75, Mn: 0.26, Mg: 0.40, Ba: 0.014, Tl: 0.033 and Sr: 0.11. This method is extremely easy, is rapid, the amount of the reagent used is a little, and a free skill and the zero emission are achieved.

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