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

Tetsu-to-Hagané Vol. 92 (2006), No. 10

  • Visualization of Collision Behavior of Particles Simulating Inclusions in a Turbulent Flow and Its Theoretical Analysis

    pp. 579-583

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    The separation of inclusions with sizes less than several micrometers is very difficult because the flotation speed of such small inclusions is slow. Thus, increasing the volume of inclusions is essential for accelerating the removal of inclusions, and several methods for enhancing collision frequency of inclusions have been proposed hitherto. Their collision behavior, however, has not been directly observed yet. In this study, by using a water model, the collision rate of particles was quantified by directly observing the particle collision behavior in a turbulent flow. The collision rate of particles directly counted by use of image analysis was compared with a theoretical collision rate, which was calculated by substituting the turbulent energy dissipation rate obtained in a numerical analysis into the Saffman-Turner's equation. In the range with large turbulent energy dissipation rate beyond 0.06 m 2/s 3, the observed collision rates deviated above the theoretical values. In view of this, the Saffman-Turner's equation has been modified for applying to the range with the large turbulent energy dissipation rate.
  • Experiment on Adhesion and Removal of Suspended Particle in Liuuid by Bubble

    pp. 584-590

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    It is widely recognized that inclusions in steel cause defects to the products. Therefore, it is important to remove inclusions from liquid steel. The attachment and removal by bubble flotation is expected as one of promising techniques for inclusion removal in liquid steel. The process of particle removal by bubbles is influenced by various factors, including the liquid flow, particle diameter, bubble size. The present work is intended to investigate experimentally the effects of some factors such as particle diameter, gas flow rate and agitation speed to particle removal rate. In this study, water model experiments on bubble flotation have been done under turbulent flow condition using a mechanically agitated vessel. It was confirmed that the change in particle concentration of suspended liquid with time shows first order kinetics until 4 minutes in the initial stage. Furthermore, it was found that the particle removal rate has increased with increasing particle diameter, gas flow rate and agitation speed.
  • Effect of HBI Utilization on Blast Furnace Productivity

    pp. 591-600

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    As an iron source of blast furnace which can adapt to recent high production rate operation and CO2 problem, reduced iron may attract attention in the near future. In this study, reduced iron melting test was performed using an experimental blast furnace with use of HBI (Hot Briquette Iron) which is one of the reduced irons in order to quantify effect of increase in production and reduction effect of reducing agent rate for blast furnace.
  • Asymmetric Rolling Theory Based on Numerical Analysis Using Orowan's Theory

    pp. 601-608

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    An asymmetric rolling possesses advantages in energy consumption, strip flatness of hot strip because of decrement of rolling force. And as we say another merit, asymmetric rolling enable us to control inner microstructure rolled with high reduction and with large shear strain. Introducing a single driven rolling to tandem hot strip rolling, we produce fine grain hot strips industrially. We need numerical deformation analysis model to combine microstructure evolution model to predict them.
    An asymmetric rolling theory based on numerical analysis using slab method, Orowan's theory, is proposed. The most important effect of an asymmetric rolling is the relative displacement of neutral points on the rolls. This displacement of neutral points generates a cross shear region in which the surface friction forces are in opposite directions. To formulate rotational equilibrium equation in the cross shear area, we consider the reasonable distribution for the pressure difference between the rolls. This developed model permits rolling load, rolling torque, stress distribution and strain distribution as a function mill geometry and strip reduction with quite short computing time. Numerical simulation results are presented and compared with results of FEM, which is most reliable to analyze plastic deformation today, and with results of laboratory rolling. Accuracy of new theory is roughly equal to accuracy of FEM.
  • Identification and Formation Mechanism of a Deformation Process Determining Microstructure of Type IV Creep Damage of the Advanced High Cr Containing Ferritic Heat Resistant Steel

    pp. 609-617

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    The microstructure of a Type IV damage, a ductile and early creep failure at outer edge of Heat Affected Zone of weld, was precisely researched. The rupture life of a simulated fine grain area of HAZ was the shortest compared with those of the other microstructures, coarse grain HAZ and dual phase HAZ, according to the temperature acceleration creep test at 700°C. The tensile strength at room temperature was the lowest at around Ac1 transformation point, determined by rapid heating diratometry. Therefore, the Type IV damage did not coincident the conventional HAZ softening phenomenon often observed in low carbon steels.
    Dislocation substructure of the fine grain zone is composed of the globular sub-grain microstructure and the coarsened carbide through the Transmission Electron Microscope observation of thin foils. They were possibly explained to be formed through the thermal cycle of HAZ and Post Weld Heat Treatment as follows: a base metal with lath martensite microstructure is warmed above Ac3 point once, and immediately cooled and transformed. Such "weak" lath martensite structure, apparent ambiguous lath martensite, was easily recovered to the globular sub-grain microstructure. Based on the hypothesis above mentioned, globular sub-grain microstructure at fine grain HAZ possibly resulted in the decrease of the creep life.
  • Creep Deformation Process Determining Microstructure of Type IV Creep Damage of the Advanced Ferritic Heat Resistant Steel with High Cr Content

    pp. 618-626

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    Type IV damage deteriorates the creep rupture strength at higher temperature than advanced Ultra Super Critical fossil power plant operation temperature, 600°C. Its metallurgical investigation is expected to avoid the creep damage at the outer edge of HAZ of welded joint.
    Metallographic analyses were carried out to clarify the micro-mechanism of Type IV failure for advanced ferritic creep resistant 9% Cr steel, ASME Gr.92. Assuming the Type IV failure arises at fine grain HAZ through the welding thermal cycle, the comparison of three candidate mechanisms, grain size refinement, dislocation sub-structure evolution and precipitation morphology development through the thermal cycle at HAZ, decided that the creep deformation process determining microstructure at HAZ is the globular sub-grain microstructure generated by thermal cycle of welding and PWHT. The creep test at 700°C of simulated globular sub-grain microstructure characterized the typical type IV phenomena on creep rupture curve. Precipitation morphology change by thermal cycle did not explain the creep time dependence of rupture strength difference between base metal and HAZ.
    Further works on the stress and temperature dependence of the creep life of Type IV phenomena is expected to subdue the creep life deterioration.
  • Substance Flow Analysis of Nickel for Risk Assessment of Nickel and Nickel Compounds in Japan

    pp. 627-634

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    Nickel compounds have been suspected of causing cancer in humans through inhalation exposure, therefore nickel compounds were specified as priority chemicals of hazardous air pollutants together with volatile organic compounds in 1997 in Japan. Thus, in this study, substance flow of nickel was analyzed from production, shipment and disposal, and the amount of domestic supply, gross additions to stock and waste generation were estimated from 1970 to 2015 in order to conduct risk assessment of nickel and nickel compounds. Additionally, sensitivity analysis was conducted in order to identify the effect to the substance flow of nickel associated with variation of uncertain parameters.
    As a result, the amount of domestic waste generation was estimated 200 thousand tons per year in 2015 as much as the amount of domestic supply. However, the amount of recovery would be increased as the improvement of rate of recovery, and the amount of incineration and landfill in 2015 would be half as much as those in 2002. Therefore, the emission of nickel into the air will decrease 4 tons per year in 2015. Furthermore, the amount of incineration was largely varied by the factors of the way of municipal waste treatment and future trend of domestic supply of other products. Thus, it was interpreted that the amount of incineration of other products should be estimated in consideration of interval analysis.
  • Numerical Model Analyses on the Effects of Steelmaking Slag Addition to Growth of the Marine Diatom Skeletonema costatum: Importance of pH Effects

    pp. 635-642

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    Numerical model analyses were made on the experimental results in order to determine the optimum amount of dephosphorized steelmaking slag addition to enhance the growth of the planktonic diatom Skeletonema costatum. In the batch culture experiments, the growth of S. costatum was optimally enhanced by an addition of 100 mg L-1 slag due to dissolution of phosphate and silicate from the slag. However, increase in pH due to the effect of calcium oxide, which is the major constituent of the slag, negatively affected on the growth. The model outputs explained the processes underlying the batch culture experiments. Further, the sensitivity analyses provided the appropriate amount of slag addition that should be applied to enhance the growth of marine diatom populations under the influence of pH increase.

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