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

Tetsu-to-Hagané Vol. 84 (1998), No. 6

  • Effect of Space Distribution around Particle on Convective Heat Transfer Coefficient of Packed Beds

    pp. 399-404

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    Convective heat transfer coefficient between a spherical particle and a liquid in packed beds were measured for the range of 77≤Re≤2000. The convective heat transfer coefficients measured by this work were quite smaller than the values obtained by the empirical equations proposed previously. Therefore, flow visualization was carried out to investigate the water flow around the particle in the packed beds. Temperature distribution and velocity of water in packed beds were also investigated by the numerical simulation.
    It was found that the space around the particle, especially the space at the flank of the particle causes decrease of convective heat transfer coefficient between a spherical particle and a liquid in packed beds.
  • The Reduction and Melting Behavior of Carbon Composite Iron Ore Pellet on High Temperature

    pp. 405-410

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    Accompanying the recent remarkable development of electric furnace steelmaking, there is an increased demand for direct reduced iron. The various methods of direct reduction iron making can be mainly classified into two groups; gas-based process and coal-based process. The gas-based process is very familiar in the world, but the fact that it relies on natural gas as its reductant means that unless the plant is located in a place with cheap access to natural gas, this process will be relatively expensive and reduce the profits from the project.
    Recently additional process is developing ; in which carbon composite iron ore pellets are reduced in a rotary hearth furnace. Their reduction rate is very fast, and they are not so severely restricted in location. Because of these points, expanded development of this process can be expected in the future.
    In development of this process, it was found that, when the reduction temperature was raised, the pellets were melted by the time of completion of the reduction, and they separated into a metallic iron and slag. If it becomes possible to produce carbon-containing metallic iron with no slag, that will reduce the energy consumption by the electric furnace, which in turn will lower the cost of producing iron.
    This paper provides a description of the fundamental study and consideration for rapid reduction and separation by means of the rapid heating of carbon composite iron ore pellets at temperatures above 1300°C, using a small electric furnace.
  • The Effect of Pressure and Oxygen, Sulfur and Nitrogen Content on the Rate of Nitrogen Absorption and Desorption of Liquid Steel

    pp. 411-416

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    The study was made on the rate of nitrogen absorption and desorption by means of vacuum induction furnace to reveal the effect of pressure on the rate of desorption of nitrogen and the effect of oxygen, sulfur and nitrogen content on the chemical reaction rate at gas-metal interface. Nitrogen desorption rate was decreased with increase in total pressure of atmosphere, which was controlled by argon gas. The apparent chemical reaction rate of nitrogen adsorption and desorption under the condition of which the mass transfer resistance in gas phase is negligible, was evaluated. Adsorption constant of oxygen, sulfur and nitrogen at 1873K was evaluated from the dependence of apparent chemical reaction rate constant on the oxygen, sulfur and nitrogen. With these values, some previously reported results of investigations on the chemical reaction rate of nitrogen are consistently concluded in the following equation.
    kr=15.9fN2/(1+173aO 52aS17aN*)2
    Calculated surface tension of liquid iron was also consistent with observed data by P.Kozakevitch et al..
  • Tensile Strength of Stainless Steel during and after Solidification

    pp. 417-422

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    Phase dependence of tensile strength of stainless steel samples during and after solidification has been investigated by a high temperature tensile test. The experimental technique enables the sample to melt and solidify without a crucible, and to measure a minute load in a solidification temperature range. The tensile strength of samples is depended on phase but not content of chromium and nickel.
    Empirical equations of the tensile strength of δ phase and γ phase are established from experimental results.
    σδ=0.013(Ts-T)+1.7, MPa
    σγ=0.061(Ts-T)+8.0, MPa where Ts is solidus temperature and T is temperature.
    The tensile strength of δ phase sample is smaller than that of γ phase, and temperature dependence of tensile strength of δ phase is smaller than that of γ phase. The tensile strength of two phase (δ+γ) is estimated from next equation.
    σ(δ+γ)δ·fδγ·fγ, MPa where, fδ and fγ are the fractions of δ phase and γ phase, respectively.
    18mass%≤Cr≤25mass%, 4mass%≤Ni≤25mass%, 1473K≤T≤1850K
    This estimated value is in good agreement with measured value.
  • Measurement of Critical Interfacial Temperature by Means of the Thermoelectric Method in Cold Sheet Rolling

    pp. 423-428

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    Temperature at the interface between roll and workpiece in cold sheet rolling is measured by the thermoelectric method. Experiments are carried out using the simulation testing machine of sliding-rolling type on various conditions of roll speed and reduction in thickness. The critical temperature is evaluated by means of investigations on the relation of measured interfacial temperatures to the occurrence of friction pick up. Relation between experimental values and theoretically calculated mean interfacial temperature is examined. The conclusions obtained are as follows ; ( 1 ) The thermoelectric method is effective for the evaluation of the interfacial temperature in cold sheet rolling. ( 2 ) The critical temperature is constant at which a friction pick up occurs from breakage of lubrication film due to frictional heating. ( 3 ) Measured temperatures coincide with calculated values.
  • Effect of Electric Current Path Area on Resistance Seam Weldability

    pp. 429-434

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    Two-dimensional model describing electric conduction and heat transfer within electrodes and plates during resistance seam welding is developed. The model is numerically solved using a finite element method. The effect of electric current path length on welding phenomena is numerically investigated. The calculation demonstrates that decrease of the current path length on the electrode/plate and plate/plate interfaces shortens the heat affected zone and that it decreases weldable current range.
    The effect of tin coating weight on the heat affected zone and weldable current range is experimentally investigated. As a result, the weldable current range and the heat affected-zone length decrease with decreasing the tin coating weight. A comparison between the calculation and the experiment shows that the experimental results can be explained by the change in the current path length. The model also predicts the experimental relation between weldability and dynamic electric resistance measured between the electrodes.
  • Elasto-plastic Stress Analysis on Formation Mechanism of Ghost-lines in Cold Rolled Steel Sheet Produced from Continuously Cast Slab

    pp. 435-440

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    Ghost-lines (GL) observed at polished surfaces of cold rolled sheets, stretched perpendicular to rolling direction, produced from continuously cast slabs were examined in order to investigate formation mechanism. Results obtained were as follows.
    ( 1 ) Degree of GL was influenced by conditions of segregations such as size, intensity, and position in the sheet.
    ( 2 ) Simulations of the GL with elasto-plastic stress analysis were carried out under an assumption that there was a difference in stress-strain curves between the sheet matrix and the segregation. It was revealed that a convex part was formed at a stretched sheet surface and the convex height was proportional to the size of the segregation and inversely proportional to the depth of the segregation part from the sheet surface. The actual behaviors of the GL in the sheet produced from continuous casting slab can be quantitatively explained by the calculated results.
    ( 3 ) From above, it was concluded that the GL was caused by existence of uneven part of mechanical properties inside the sheet.
  • Phase Transformation Mechanism of Ferritic Stainless Steel by Nitrogen Absorption

    pp. 441-445

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    Fe-Cr binary alloys with 12mass%Cr or more are originally fully ferritic in a high temperature range, put the crystal structure can be changed from bcc (ferrite) to fcc (austenite) by nitrogen absorption in latm N2 gas atmosphere at 1473K. In this paper, the mechanism of the phase transformation with nitrogen absorption was investigated in association with crystallographical characteristic by means of optical microscopy and scanning electron microscopy. The alloy used is a 27mass% Cr ferritic stainless steel. This steel can absorb a great amount of nitrogen (about 1.4mass% at the maximum) in latm N2 gas atmosphere at 1473K, so that the austenite formed at the temperature is kept to be stable even at room temperature. Results obtained are as follows:
    ( 1 ) The austenite formed by nitrogen absorption has the Kurdjumov-Sachs orientation relationship with ferritic matrix : (111)γ//(011)α, [101]γ//[111]α
    ( 2 ) The austenite grows in rod-like shape toward one of four <111>α directions, and the side faces of rod-like austenite is confirmed to be constructed with two kinds of γ/α interfaces which have a good coherency in the Kurdjumov-Sachs orientation relationship.
  • Effects of Alloying Elements and Carbon Potential on the Amount of Retained Austenite of Carburized Steel

    pp. 446-451

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    The effects of alloying elements and carbon potential on the amount of retained austenite in carburized steels were investigated. First, the Ms temperature of high carbon steels was measured by means of a dilatometer. In high carbon region, the contribution of carbon content to Ms temperature became smaller than that of medium carbon steels, while the contribution of Mn, Cr and Mo which are substitutional elements became larger.
    Next, 1.0mm thick specimens were gas-carburized at 1203K for 108ks to reach equilibrium, quenched into oil and tempered at 443K for 7.2ks. The equilibrium carbon content, which increased with increasing Mn, Cr and Mo content but decreased with increasing Si and Ni content, could be calculated from carbon potential in atmosphere and interaction parameters of carbon on these alloying elements. The amount of retained austenite could be calculated from the Ms temperature of high carbon steel as a function of the equilibrium carbon content, and a parameter which should be determined by quenching and tempering condition.
    These results indicate that it is important for calculation of retained austenite content of carburized steels to take into account the change in contribution of alloying element to Ms temperature in high carbon region and the change in equilibrium carbon content due to chemical composition of steel.
  • Fracture Toughness and Microstructure in TiB Particulate-reinforced Ti-6Al-2Sn-4Zr-2Mo Composites

    pp. 452-457

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    Fracture characteristics and fracture mechanism of TiB particulate-reinforced Ti-6Al-2Sn-4Zr-2Mo composites with various volume fraction of TiB particles fabricated by blended elemental method were investigated by carrying out static and dynamic fracture toughness tests.
    Both static and dynamic fracture toughness values decrease with increasing the volume fraction of TiB particles. The dynamic fracture toughness value is fairly smaller than the static fracture toughness value. The ratio of dynamic fracture toughness value to static fracture toughness value increases as the volume fraction of TiB particles increases. The fracture toughness values increases with increasing the degree of crack deflection which is greater under static conditions than under dynamic conditions. The fraction of TiB particles on the fracture surface is greater in the specimen with greater volume fraction of TiB particles, and is greater under dynamic conditions than under static conditions.
  • Effect of Heat Treatment on Hardness and Electrical Resistivity of Ti-10V-2Fe-3Al Alloy

    pp. 458-463

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    The properties of Ti-10V-2Fe-3Al which is a precipitation hardnable alloy depends on heat treatment condition. The relationship between hardness and electrical resistivity changes was studied at various solution and aging temperatures. The changes of these properties with aging was related to each other because of α phase precipitation. Also the activation energy obtained by electrical resistivity changes for α phase precipitation on aging was found to be nearly constant at different solution temperatures above β transus or below.
  • Crystallization Behavior of Li2O-SiO2, Na2O-SiO2 and Na2O-CaO-SiO2 Glasses

    pp. 464-469

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    It has been known that crystallization of mold powder is effective on the disturbance of heat transfer between mold and solidified shell in production of middle carbon steel slabs in continuous casting process. But it has not yet been made clear which composition of mold powder is the most suitable for crystallization.
    The crystallization behavior of Li2O-SiO2, Na2O-SiO2 and Na2O-CaO-SiO2 glasses was observed by differential thermal analysis (DTA) and hot-thermocouple methods with DTA in the present work. As a result, addition of alkaline metal and alkaline earth metal oxides to SiO2 increased the critical cooling rate for glass formation in binary system of Li2O-SiO2 and Na2O-SiO2, and Li2O-SiO2 system crystallized easier than Na2O-SiO2 system. In ternary system of Na2O-CaO-SiO2, addition of Na2O hurried the critical cooling rate at CaO/SiO2= 0.93 mass ratio, but the rate was almost constant in the composition range of more than 15 mass% Na2O. The slag of CaO/SiO2=0.93 made the rate faster than the slag of CaO/SiO2=0.47 at constant content of 10mass% Na2O.

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