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

Tetsu-to-Hagané Vol. 77 (1991), No. 9

  • Computer Simulation and Control of Processes in Shape Casting

    pp. 1381-1389

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  • Production of Metallic and Oxide Ultrafine Particles in Liquid-phase and Their Surface Characteristics

    pp. 1390-1398

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  • Threshold Stress in Dispersion Strengthened Alloys at High Temperatures

    pp. 1399-1406

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  • Percolating Velocity of Fine Particles through Packed Bed of Coarse Particles

    pp. 1407-1412

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    The percolating velocity of fines through the packed bed of glass beads of 4.5 and 12 mm in diameter and silica gel spheres of 1.5 mm in diameter was measured with bifurcated optical fiber probes. Silica-alumina particles of 68 μm, alumina particles of 211 μm and glass beads of 398 μm were coated with a fluorescent dye, and were used as a tracer. When 12 cm3 of the tracer particles was injected in the gas flow and exposed to ultraviolet light which was introduced with the silica fiber, visible light was emitted and transferred outward with the plastic fiber. The percolating velocity of fines was determined from the time period to pass the distance between the probes.
    The ascending velocity of fines increased with increasing gas velocity and size of packed particles. A flow model of fines was proposed on the basis of the successive collision of fines on coarse particles. The percolating velocity of fines agreed with the calculated value. The measuring system developed was proved to be able to detect the local percolating velocity of fines in packed bed. The ascending velocity near the column wall was higher than that in the core region.
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    2. Analysis of Steam Flow in Coke Oven Chamber Tetsu-to-Hagané Vol.77(1991), No.8
    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8
  • Direct Measurement of Ascending Flow of Fines through Packed Bed of Coarse Particles

    pp. 1413-1418

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    Silica-alumina particles of 68 μm diameter were continuously fed at the bottom of a bed packed with glass beads of 4.5 mm diameter and were entrained upward through the bed. A small amount of tracer particles was injected into the gas-solid flow, and the ascending velocity of the fines was measured directly using bifurcated optical fiber probes. The dynamic hold-up of fines in the bed was determined from the weight of elutriated particles after the supply of fines was suddenly stopped. Then the gas velocity was much increased, and the entrained particles was assigned as the static hold-up. The ascending velocity of fines was a little dependent on the feed rate of fines, and the value near the column wall was higher than that in the core region. The successive collision model proposed was effective to explain the behavior of fines in the gas-solid flow through the packed bed.
    x

    Readers Who Read This Article Also Read

    1. Circulation and Reduction Behavior of Iron Ore in Circulating Fluidized Bed Tetsu-to-Hagané Vol.78(1992), No.7
    2. Analysis of Steam Flow in Coke Oven Chamber Tetsu-to-Hagané Vol.77(1991), No.8
    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8
  • Activity Measurement of the Constituents in FetO-MnO Slag Equilibrated with Iron

    pp. 1419-1425

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    Measurements have been made to study the equilibrium between H2O /H2 gas mixture and FetO-MnO melt in Fe crucible at 1 450 and 1 500°C. The influence of slag composition on the activity of iron oxide and Fe3+/Fe2+ ratio has been clarified.
    The activity of MnO in FetO-MnO slag in equilibrium with iron and the oxygen content in liquid iron equilibrated with this slag have been calculated using α-function of FetO. As the result, it has been confirmed that Fet-MnO slag shows approximately ideal behaviour. Furthermore, the dissolved oxygen content in liquid iron equilibrated with FetO-MnO slag has been evaluated based on the present results.
  • Bubble Characteristics in the Buoyancy Region of Air-Water Vertical Bubbling Jet

    pp. 1426-1433

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    The flow field in vertical bubbling jet in a cylindrical vessel with bottom blowing can be divided into four regions. They are named the momentum, transition, buoyancy and surface region from the nozzle exit. In a previous paper, bubble behavior characterized by gas holdup, bubble frequency, bubble rise velocity and so on was clarified for the momentum region in which inertia force of injected gas played an important role. In the present study, bubble behavior in the buoyancy region in which buoyancy force of bubbles governed the flow was investigated by means of two kinds of electro-resistivity probes, a high speed video camera, and a laser Doppler velocimeter. The bubble behavior was not affected by nozzle diameter and bath diameter. Therefore, correlations for gas holdup, bubble frequency and bubble rise velocity were proposed as functions of gas flow rate.
  • Shape Control of Molten Metal Puddle by Directly Imposing Electric Field between Rolls and Magnetic Field in the Casting Direction in Twin Roll Process

    pp. 1434-1441

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    A new process to control the side edge shape of molten metal puddle is proposed in which direct electric field imposed between rolls and direct magnetic field applied in the casting direction induce electromagnetic force in molten metal puddle. The experimental works were carried out to clarify the possibilities of holding molten metal at side edge and of controlling the side edge shape by the electromagnetic force. It was found that the holding height of meniscus can be controlled by the direct electric current as an operating parameter. This method to hold molten metal at side edge is named an electromagnetic dam. And it was noticed that using the shape control function of electromagnetism the saw shape edge on cast sheet, which is attributed to the instability of meniscus, becomes smoother than that obtained by the previously proposed process in which only direct magnetic field was imposed to suppress the saw shape edge. The experimental data verify the mathematical model of the electromagnetic dam which can predict the holding height of meniscus position of molten metal puddle from electric current, magnetic field and casting velocity.
  • Experimental Measurements and Theoretical Analysis of Induction Heating by Use of a Conductive Crucible

    pp. 1442-1449

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    In order to improve the energy efficiency of a segmented conductive crucible, experimental measuerments and theoretical analysis have been conducted.
    When the segments of the crucible are electrically shorted at the bottom, the magnetic filed intensity in the crucible is decreased by decreasing the longitudinal distance between the coil and the short circuit part of the crucible. When the segments of the crucible are insulated each other, the magnetic intensity is scarcely influenced by changing the relative position of the coil and the crucible. The effect of crucible length on magnetic field distribution is not clearly appeared in the both cases in which the segments of the crucible are electrically shorted and insulated. These experimental results are explained by a mathematical model. A new induction heating process in which segments are not cooled unlike the cold crucible has been proposed and named a hot crucible. From the measurments of heating rate of the charges under both the cold crucible and the hot crucible conditions, the heating under the latter was found to be about 1.72.5 times faster than that under the cold crucible condition.
  • Impact Pressure of Water in Hydraulic Descaling during Hot Strip Mill Rolling

    pp. 1450-1457

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    Hydraulic descaling is commonly used to remove scale formed during reheating and continuous rolling of steel strips.
    On an experimental survey of parameters which affect the descaling behaviour, impact pressure was measured precisely both by spraying over a plasticine ( a modelling material) on the basis of design of experiments and by using a pressure converter. It was found that the impact pressure has good correlations with the water consumption V at a pressure of 9.8 MPa, water pressure P, rolling speed v and distance H between the material and the nozzle.
    The thickness loss Δt of plasticine and the impact pressure p by hydraulic descaling can be then expressed by the descaling parameters as follows;
    Δt = 2 000 PV/ ( vH2 ) ( cm, correlation coefficient : 0.94)
    p = 5.64 PV/H2(MPa)
    The impact pressure calculated from the equation is in excellent agreement with H. HOJAS' results.
    Since the impact pressure required to remove the primary scale is much higher than secondary scale, a careful set up of the conditions is essential to complete the descaling.
  • Temperature Drop of Steel by Hydraulic Descaling for a Hot Strip Rolling Mill

    pp. 1458-1464

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    When scale formed during reheating and continuous rolling of steel strips is commonly by hydraulic descaling, a temperature drop of the strips inevitably occurs.
    On an experimental survey of parameters which had been expected to control the descaling behaviours, the temperature drop of steel strips on removing the secondary scale by hydraulic descaling was measured precisely on the basis of design of experiments. It was found that the temperature drop has correlations with the water consumption V at a pressure of 9.8 MPa, interaction between V and the distance H between the steel and the nozzle, water pressure P.
    The temperature drop ΔTD(°C) of steel strips by hydraulic descaling can be then expressed by the descaling parameters as follows;
    ΔTD= 451.7 PV/H2+9.54
    It is concluded that H should be increased with V to keep the temperature drop small when a certain pressure impact pressure is required to remove the secondary scale.
  • Characteristics of Rolling Load, Strip Shape and Strip Surface in Cold Rolling of Stainless Steel Foil

    pp. 1465-1472

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    A demand of stainless steel foil has been recently increasing in electronic apparatuses, electric cells and construction materials. Main subjects in cold rolling of stainless steel foil are strip shap like flatness and fine wrinkles, and surface conditions of rolled strip like gloss and roughness. This paper shows the characteristics of rolling, strip shape and strip surface in cold rolling of stainless steel foil which were obtained by experiments of cold rolling in a twelve-high cluster mill. Main results are as follows. Controllability of strip shape increases more by using doubled-tapered intermediate rolls than by using single-tapered ones. Surface gloss of rolled strip increases with the decrease of surface roughness of work rolls and rolling speed, and with the increase of reduction in thickness.
  • Experimental Determination of Isothermal Section at 1 273 K in the Ternary Ni-Cr-N System

    pp. 1473-1480

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    An isothermal section of the equilibrium phase diagram in the ternary Ni-Cr-N system was experimentally determined at 1 273 K. Binary Ni-Cr alloys with chromium concentration from 20 to 79 mass% were nitrided in pure nitrogen gas under various pressures between 10 and 96 kPa at 1 423 or 1 523 K. The ternary Ni-Cr-N alloys prepared by the nitriding were equilibrated at 1 273 K for time varying between 2.0 × 106 and 3.7 × 107 s. The concentration of nickel and chromium of each phase in the equilibrated alloys was determined by conventional electron probe microanalysis. Nitrogen in solid solution phases and nitrides was analyzed by a refined method of electron probe microanalysis, which has been recently established by the present authors.
    A nitride with the metal-atom arrangement of β manganese, which is designated as a π phase, was found to be in equilibrium with a nickel-rich fcc-γ phase, a chromium-rich bcc-α phase, and a di-chromium nitride, which is designated as an ε phase. The chemical compositions of the π and ε phases observed in the present work led to the formulae of Cr12(Ni0.94-0.97 Cr0.06-0.25)8 N3.9-4.2 and (Cr0.99 Ni0.1)2 N0.80-0.97, respectively. The π phase became unstable above 1 473 K. This explains a previous unsuccessful attempt to make the Ni-Cr-N ternary π phase by replacing molybdenum in Mo12Ni8N4 with chromium.
  • Effect of Cooling Rates on Microstructures of β Treated α+β Titanium Alloys

    pp. 1481-1488

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    Effect of cooling rates after β treatment on microstructures in two α+β titanium alloys, Ti-6Al-4V and Ti-6Al-6V-2Sn, is examined.
    From the microstructural examinations and hardness measurements, cooling rates are classified into three regions. In the first region ( lower than 10°C/s in Ti-6Al-4V and 4°C/s in Ti-6Al-6V-2Sn), dependence of hardness on cooling rates is relatively small and a few dislocations are involved inside the transformed plates. In the second region (10300°C/s or higher cooling rates in Ti-6Al-4V, 4 20°C/s in Ti-6Al-6V-2Sn), hardness strongly increase with the increase of cooling rates, and highly dense dislocations are included in the plates, although diffusion of solute atoms are expected. In the third region ( higher than 20°C/s in Ti-6Al-6V-2Sn), hardness shows a constant and high value which is independent of cooling rates. In Ti-6Al-6V-2Sn cooled at the cooling rate of 300°C/s, there are quite many micro-twins or stacking faults in the acicular type of plates and little amount of diffusion is detected.
    It is considered that diffusional component and shear one of transformation mainly operate at the cooling rates in the first and third regions, respectively. At the cooling rates in the second region, both components operate competitively during cooling.
  • Toughening in Weld Joint of Ti-15V-3Cr-3Sn-3Al Alloy with Heat Treatment

    pp. 1489-1494

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    A modified heat treatment process has been developed to maintain high strength levels of the base-metal and to enhance fracture toughness of the weld joint in welded materials of Ti-15% V-3% Cr-3% Sn-3% Al alloy used for spherical rocket moter cases of upper stages for scientific satellites. The hardness became relatively high at the weld joint with conventional heat treatment process. This local increase in the hardness results in a decrease of the fracture toughness of the weld metal. In order to reduce slightly the hardness only at the weld joint, the materials were aged at relatively low temperature ( designated as preaging) after solution treatment, and then welded and conventionally aged ( designated as secondary aging). The mechanism to improve the mechanical properties is considered as follows. At first, almost all parts are uniformly hardened with the preaging. Then the hardness of the weld joint is sharply reduced due to TIG welding because of re-solution treatment, while the base-metal maintains the high hardness. At the last step of the secondary aging, the hardness at the base-metal is increased in terms of the second step aging but the weld joint is hardened up to the level slightly down that of the base metal. Consequently this process has made it possible to obtain the desirable mechanical properties.
  • The Effect of Addition of Alloying Elements on the Crevice Corrosion Resistance of Titanium in Hot Salt Solutions

    pp. 1495-1502

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    Effect of single and double addition of various alloying elements (Pd, Ni, Co, Mo, W, V, etc.) on the crevice corrosion resistance of titanium in 1.03 or 4.27 mol/l NaCl solution with pH range of 2 to 6 test conditions has been examined in high temperature salt solutions. As a result, it was observed that most effective element, addition of 0.05% Pd being sufficient to prevent crevice corrosion up to 473 K. Double addition of Pd and Co was further effective. Relationship between the effect of alloying elements on the crevice corrosion resistance and the acid corrosion resistance was also confirmed. Reasons for those effects were discussed based on electrochemical measurements.
  • Accelerated Oxidation of Single Crystal Ni-10Cr-12Al-Ta-W Superalloys Coated with a Na2SO4-NaCl Salt

    pp. 1503-1510

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    The behavior of the accelerated oxidation in a Na2SO4-NaCl salt was investigated for nickel-based single crystal superalloys for turbine blades and the other applications. In particular, attention was directed towards the tungsten effect on the oxidation behavior. For this purpose, several alloys with varying tungsten contents were prepared for a Ni-10Cr-12Al-W-Ta system. The accelerated oxidation curves were obtained using a thermo-balance and the corrosion products were identified by EPMA and a conventional X-ray diffraction method. As the tungsten content increases, the oxidation curves became complicated and showed poor hot-corrosion resistance. It was found from the identification of the corrosion products that the accelerated oxidation occurred in this alloy system by a mixed mechanism of the basic-and the acidic-fluxing. Furthermore, it was suggested that the amount of a precipitated α-W phase could be a measure for the hot-corrosion of these alloys coated with a Na2SO4-NaCl salt.
  • Stress Corrosion Cracking of SUS316L Stainless Steel in the Chloride Solution Containing Thiosulfate Ion by the Slow Strain Rate Technique

    pp. 1511-1518

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    Stress corrosion cracking (SCC) behavior of SUS316L stainless steel in the chloride solution containing thiosulfate has been investigated by using a slow strain rate technique (SSRT). The susceptibility of SCC was found to depend on the strain rate, the concentration of thiosulfate and chloride, and pH. The highest susceptibility was obtainedat the condition of 20 mass% NaCl containing10-2kmol·m-3 Na2S2O3 at pH 5.3 and 2.2 ×10 -7 s-1. Observations of fractured specimens showed that cracks perpendicular to the tensile axis generated at the pits. The initial fracture mode of the crack was intergranular, followed by transgranular and dimple with propagation of the crack. Intergranular fracture initiated from intergranular corrosion on the bottom of the pit, in which pH decreased less than 2. Immediately after immersion, pits generated easily because the dissolved oxygen with thiosulfate rapidly raise free corrosion potential upto pitting potential in cooperation with the action of thiosulfate to lower the pitting potential. Decrease in pH caused lowering of pitting potential and increase of the number of cracks, while the highest SCC susceptibility was obtained at pH 5.3. At conditions showing the high SCC susceptibility, corrosion potential was always in the range between -400 and -370 mV (Ag/AgCl). Therefore, the SCC behavior in this system is strongly controlled by the electrochemical factors.
  • Effect of Prior Deformation on Grain Refining Process of Martensitic Shear Reversion in Metastable Austenitic Stainless Steel

    pp. 1519-1526

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    Effect of prior deformation on the martensite shear reversion mechanism of the lath martensite to austenite and the grain refining of the reversed austenite has been investigated in a metastable austenitic 14.25%Cr-10.94%Ni steel in terms of the microstructures. The steel used transforms to almost fully lath martensitic structure through 60% cold rolling at room temperature. Further cold rolling above 60% results in an additional deformation to the lath martensite. Martensite lath structures are significantly damaged on and around the slip bands and dislocation cells are formed in the damaged areas. The volume fraction of damaged areas increases with increasing deformation rate.
    The lath martensite reverts to austenite abruptly with a martensitic shear between 800 K and 900 K, independing on prior deformation. The reversed austenite in the undamaged areas receives the microstructural characteristics of martensite after the reversion. Lath austenitic structure, which is constructed by austenitic, laths and blocks, are formed in the undamaged areas and the traces of slip bands exist in the damaged areas of reversed austenite as a line of dislocation cells. In the undamaged areas, the lath austenitic structure recovers very slowly. Dislocation forms cell structure in the austenitic blocks and the cell structure changes to subgrains. In the damaged areas, recovery of the reversed austenite proceeds very fast and fine recrystallized austenite grains are formed along the traces of slip bands in a short time annealing. In order to obtain uniform fine austenite grains, a lot of slip bands should previously be introduced by heavy cold rolling in the lath martensitic structure.
  • Development of On-line Analytical Method for Hydrogen in Molten Steel at Vacuum Degassing Process

    pp. 1527-1532

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    Degassing operation in the steel making process is important in the production of low-hydrogen steel. The conventional analytical method for hydrogen in molten steel with sampling using a quartz tube takes a long time, and has insufficient accuracy. A direct analytical method for hydrogen in molten steel has been developed to solve these problems. In this system, a refractory probe is immersed in the molten steel and inert gas is blown through it into the molten steel. The hydrogen concentration in molten steel is then continuously measured by recovering samples of gas that has reached equilibrium in floating upward to a specified level in the ladle. This new analytical system is installed at the RH vacuum degasser of the steel making plant, and is being tested for its application to commercial operation. During degassing operation, the analytical values obtained by the proposed method well agree with those by the conventional method in the low concentration range. On the other hand, the proposed analytical method yields higher values in the high concentration range, probably because of the escape of hydrogen from the sample during and after sampling in the conventional method. The new analytical method can continuously measure the hydrogen concentration of molten steel in 2.5 min, about one-tenth of the analytical time of the conventional method.
  • Observation of Fine Structure in Auger Electron Spectra for Chemical State Analysis

    pp. 1533-1537

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    Cooperative researches by 8 laboratories were carried out to observe fine structure in Auger spectra for chemical state analysis. In general, structure due to chemical effects can be observed from metals and non metals in conventional electron excited AES.
    After the observations of fine structure in AES by using Au, Fe, Ni, Al and their oxide samples, the following results could be obtained.
    1) When the instrumental condition and the sample position are normalized by the electron elastic scattering profile, the energy observed with various instruments have the almost same value.
    2) Auger profile (peak intensity) varies according to the instruments and the measuring conditions utilized.
    3) When sharp Auger spectra appear at the close energy range each other as the case of Fe LMV/Fe LMM, the differrence of the spectral intensity ratio between metal and oxide samples is small, but the small deviation of them, as the case of Fe LVV/Fe LMM whose energy is not close as the case of Fe LMV/Fe LMM, can be applied to the chemical state analysis.

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