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

Tetsu-to-Hagané Vol. 64 (1978), No. 12

  • 随想

    pp. 1659-1660,1794

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  • A Development of Automatic Coal Petrographical Analyses for Evaluating Coking Coals

    pp. 1661-1670

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    An automatic system for measuring the distribution of reflectances of coal petrographical constituents has been developed. The system is consisted of an apparatus for microphotometric reflectances of coal and analytical programs. The apparatus is composed of a microscope, phto-cell, and mechanical scanning stage which is controlled by a computor, and measure & reflectance at 20000 to 100000points in a sample in 30 minutes to 2 horus.
    The out-put data from the photo-cell are sent to the computer and transfered to absolute reflectances which has been previously compared to the standard samples, and then accumlated and stored to a disc-file of the computer. The accumlated data are retrieved at any time as the distribution of reflectances, which can be shown as a figure of numerical values.
    The system possesses an ability to detect Vitrinit only, and thus one can obtain the distribution of reflectances of whole other macerals as well as of Vitrinit.
    By the analytical program whic can eliminate the boundary effect of coal grains and binder and can recognize each macerals, coking properties of various types of coal and blend can be estimated.
    Now the system can be used practically in the following applications, producting excellent results:
    1. Making a blending plan for coke plants by estimating the coke strength of coal blends.
    2. Quality inspection of purchased coal.
    3. Determination of coal quality from an outcrop or boring core samples in an undeveloped coalfield.
  • Comparative Studies of Kjeldahl Method and Dumas' Method on the Determination of Nitrogen in Coke

    pp. 1671-1675

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    The establishment of an accurate analytical method of nitrogen in coke has recently become important in connection with the reduction of nitrogen oxides (NOx) in flue gas from iron ore sintering plants.
    The wet method (Kjeldahl method) and dry one (Dumas' method) have been widely used for the determination of nitrogen in coke.
    In a recent paper, however, it was reported that the difference of analytical values was observed between Kjeldahl method and Dumas' method on the analysis of nitrogen in coke and the former has generally given lower values.
    Therefore, the authors carried out experiments to confirm this point and also to clarify the reason of the difference between the two methods by using various coals, cokes, and organic reagents.
    As a result, the following points became clear.
    (1) No nitrogen was detected in the insoluble residue after the cokes had been treated by Kjeldahl method. Therefore, the reason why the wet method gives lower values can not be attributed to the dissolution method of samples.
    (2) The reason can be ascribed to the existence of nitrogenous radicals which are contained in coal (raw material of coke) and will not easily change into ammonia.
    (3) Only bituminous coal and coke produced from the coal showed considerably large difference compared with any other coal and coke.
    (4) Bitiminous coal contains much nitrogenous radicals in comparison with other kinds of coals.
  • A Theoretical Analysis on Gas Flow and Heat Transfer in Packed Beds with Fused and Unfused Layers

    pp. 1676-1684

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    A mathematical formulation was proposed for the simulation on simultaneous gas flow and heat transfer in the packed bed with fused and unfused layers for providing the mechanism of heat transfer in the lower part of the blast furnace. The model consisted of heat balances on gas and solids and of the multidimensional Ergun equation as the equation of motion. Therefore, it can predict distributions for mass velocity of gas and for temperatures of gas and solids. Numerical computation was performed for various degree of fusion and also for different inlet flow rate of gas.
    The computed results show that fused layer is essentially heated up by heat exchange between gas and solid for the low degree of fusion, whereas, for the case of the high degree of fusion, it is done principally by heat conduction from the surrounding unfused layer where preferential flow of gas would present and, as the results, temperature would be increased rapidly.
  • Analysis of Effective Distribution Coefficient Based on Transport Phenomena in Liquid and Solid Region

    pp. 1685-1693

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    Taking account of the simultaneous heat and mass transfer in liquid and solid region, mathematical formulations are developed to describe the solute redistribution in dendritic solidification of alloys.
    Namely, an analytical solution is presented under the conditions of the negligible undercooling in liquid and solid region and the complete mixing in liquid phase. Moreover, both the relation between the solid fraction and the concentration and that between Péclet number (Rl/E) and the physical properties of metal are mathematically presented. In addition, four kinds of effective distribution coefficients which are indispensable for the explanation of dendritic solidification are defined and given by the analytical expression.
  • Mechanism of Deoxidation with Silicon in Inductively Stirred Liquid Steel

    pp. 1694-1703

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    The rate of deoxidation with silicon and silicon-calcium alloys in inductively stirred liquid iron was studied to make clear the mechanism of deoxidation in such stirred system. Some proposed models were discussed to explain the behaviour of small particles formed by deoxidation. The results obtained are summarized as follows: 1. The process of deoxidation by the addition of deoxidation elements consists of the three stages of incubation period, rapid-decreasing period, and slow-decreasing period. 2. The number of particles and size of deoxidation products are governed by the supersaturation at a moment of addition. The number of particles increases and particles diameter decreases with increasing supersaturation in the melt. 3. The growth of the particles takes place on two steps, that is, very rapid growth at a moment of addition and slow growth subsequently to the formation of small particles. The former is controlled by the diffusion of the solute to the nuclei of deoxidation products, and the latter is proceeded by the collision of particles due to velocity gradients in turbulent flow. 4. The particles in stirred melts are removed by the collisions of particles on the crucible walls. 5. The rate of deoxidation with silicon-calcium alloys is rather slow compared with deoxidation by silicon due to the formation of very fine particles as the deoxidation products.
  • Rate of Desulfurization of Liquid Iron by CaO-SiO2-Al2O3 Slag and Interfacial Phenomena

    pp. 1704-1713

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    The rate of desulfurization of liquid iron in an alumina crucible by CaO40%-SiO240%-Al2O320% slag was studied at about 1550°C. At the same time, the change of interfacial tension during desulfurization was examined by the X-ray photography.
    The rate of desulfurization incereased in order of pure iron, iron containing silicon, and iron saturated with carbon. From the analysis of experimental results by the rate equation of the mixed-controlled reaction model, it was found that the partitioning of sulfur between liquid iron and slag at the interface reached its equilibrium one in the case of liquid iron without carbon and not in the case of liquid iron containing carbon. This indicates that the rate controlling step is the mass transfer in the former and the chemical reaction in the latter.
    The overall rate constants ranged from 9.2×10-6 to 4.9×10-4 cm/sec.
    The interfacial tension incereased monotonously with the progress of desulfurization and showed no abnormal change. It decreased remarkably with increase of the activity of sulfur in liquid iron.
  • Gas Holdup and Average Rising Velocity of Bubble Swarms

    pp. 1714-1722

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    The gas holdup and average rising velocity of bubble swarms in a mercury bath have been studied by using an electroresistivity probe method. The column diameter was 7 cm and the bath depth was 40-70 cm. Nitrogen was blown through a nozzle (O.D. ×I.D. =0.7×0.2, 0.4×0.24cm) into the bath. The gas-flow rate was 160-1330 (cc/sec, 1 atm). It is found that the gas holdup is 0.073-0.28 and the average bubble rising velocity is 50-100 (cm/sec). The gas holdup of the present nitrogen-mercury system is nearly equal to that of the air-water system. Equations are obtained to describe the effects of physical properties of gas and liquid on the gas holdup. The equations are used to explain the close agreement of the gas holdup between the two systems. The effects of column and nozzle diameters on the gas holdup are also examined. From theoretical analyses of the data, the gas holdup and average bubble rising velocity are estimated for the nitrogen-molten iron system.
  • Low Temperature Ductility and Dislocation Structure in α-Iron Containing Second Phase Particles

    pp. 1723-1729

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    The relation between dislocation structures and low temperature ductility of ferritic irons containing two kinds of finely dispersed particles (ε-Cu and TiN) was investigated as a function of various prestraining conditions, i. e. prestraining temperature, quantity of prestrain, and annealing or strain aging after prestraining.
    ε-Cu particles in Fe-1.83%Cu alloy were dispersed by aging for 96h at 700°C and TiN particles in Fe-0.1%Ti alloy were distributed by internal nitriding at 850°C.
    Low temperature ductility (77K) of aged Fe-Cu alloy increased about 3 times by 3% prestrain at room temperature and by prestrain up to 12% at 153 K followed by 2.5% strain at room temperature. The ductility, however, did not increase when the alloy was annealed for 1 h at 700°C or was strain aged for 20 min at 150°C after prestrainig at room temperature. No change in low temperature ductility of ferritic iron containing TiN particles was observed after prestraining at room temperature.
    In the ferritic iron with good ductility at low temperature such as internally nitrided Fe-Ti alloy or Fe-Cu alloy prestrained about 3% at room temperature, dislocation structures were found to be composed of tangles around particles or cell connecting particles.
  • Effect of Rolling Temperature on Strength and Low Temperature Toughness of Fe-13%Ni Alloys

    pp. 1730-1736

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    Thermomechanical treatment was applied to Fe-13%Ni cryogenic alloys for the improvement of the strength and the toughness. The rolling temperature was varied and the relative appreciation was made on the proof stress at 300 K and the impact energy at 77 K of the alloys thermomechanically treated at various temperatures of 900°C, the lower austenite temperature region, 650°C, the α-γ two phase region and 23°C. In the material treated at latter two temperatures, no difference was observed in the combination of the strength and the low temperature toughness. The better combination was obtained by rolling at 900°C and reheating. Anisotropy of the impact energy at 77 K was found to be increased with increasing the strength.
    The addition of Ti together with Mo showed marked increase in strengthening and increased the strength of Fe-13%Ni alloys without reducing the low temperature toughness.
  • Macroscopic and Microscopic Processes in the Delayed Fracture Crack Growth of High Strength Steels

    pp. 1737-1746

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    A detailed study was made of the macroscopic and microscopic fracture behaviors in slow crack growth process for a JIS SNCM 8 steel (AISI 4340) and for an SNCM 23 steel (AISI 4320) immersed in distilled water as a function of applied stress intensity factor KI at various temperatures. The crack growth rate changed following after the change of temperature during growth process without delay, but an incubation time was observed with decreasing KI depending on the change in stress intensity factor ΔKI. It was found that the crack growth occurred as discontinuous steps for all test conditions. The frequency of microscopic crack jumps was strongly dependent on testing temperature while virtually independent of KI, and the crack jump distance was not influenced by temperature but might be related to microscopic nature of crack ing mechanics. Furthermore, it was indicated that the time intervals between crack jumps were controlled by a thermally activated process with apparent activation energy of about 9000 cal/mol. These experimental data may be considered to make proof of hydrogen embrittlement mechanism in slow crack growth process with the assumption that the critical hydrogen concentration required for crack growth is inversely proportional to KI.
  • Effect of Strain Aging on Strengthening of 25Ni Maraging Steel Containing Co and Mo

    pp. 1747-1755

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    In order to strengthen 25Ni maraging steel containing Be, Ti and Al, effects of combined additions of Co and Mo, and strain aging have been investigated.
    For 23.5Ni-9.1Co-5.3Mo-0.68Be-0.30Ti-0.25Al alloy, 295 kg/mm2 tensile strength and 1.7% elongation are obtained by aging treatment at 450°C for 1 hr after cold working with 64% reduction of area. Dilation, electrical resistance and specific heat measurements reveal that there is no essential difference in the aging behavior between conventional aging and strain aging. But precipitation and austenite reversion can occur in strain aging at a temperature lower than 30°C in conventional aging.
  • Effects of Ti Addition on the Corrosion Resistance of 13Cr Stainless Steels with Extremely Low Carbon and Nitrogen

    pp. 1756-1763

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    The effects of Ti in 13Cr stainless steels containing only about 0.01% C and N upon the corrosion resistance and the properties of passivation and passive state, were investigated in comparison with the commercially produced AISI type 410 and 430 stainless steels.
    The experimental results showed that, by the addition of about 0.3% Ti, 13Cr stainless steels containing about 0.01% C and N were superior to AISI type 430 stainless steel in general corrosion resistance. The improvement of corrosion resistance by the addition of Ti was attributable to the decrease of the critical anodic current density and to the shift of the potential to less noble direction. It was confirmed that this beneficial effect was brought by Ti as solid solution. With regard to the properties of passive film, it was concluded that the decrease of C and N to 0.01% level in ferrific stainless steels led to the increase of the quantity of coulomb for reduction of passive film and that the addition of Ti at solid solution state resulted in an improvement effect on the passive film in quality, consequently 13Cr stainless steels containing Ti and extremely low C and N showed higher stability in passivity than commercially melted AISI type 430 stainless steel.
  • Wear Resistance of Deposited Iron Alloy with High-Carbon and High-Vanadium

    pp. 1764-1770

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    The present study was undertaken to clarify the relationship between the wear resistance and structure of deposited iron alloy containing high-carbon and high-vanadium. In order to study the effect of size and distribution of vanadium-carbide and surface condition on the wear resistance of the alloy, vanadiumcarbide and in the specimens were controlled from 8 to 55% in volume. Measurement of the wear properties was done using a specially designed apparatus. Specimens were tempered at various temperatures.
    The results of observation are summarized as follows: (1) Under the condition which brings a large amount of wear, the alloy including big size vanadium-carbide particles showed better wear resistance than it's fine size vanadium-carbide particles. On the other hand, the alloy including fine vanadium-carbide was better under the condition which brings a little amount of wear.
    (2) In wear properties, the alloy including vanadium-carbide was superior to the alloy including chromium-carbide.
    (3) Effect of heat treatment on the wear resistance was distinguished remarkably under the condition which brings a large amount of wear. Influence of the amount of vanadium-carbide on the wear resistance was more notable in annealed specimens than quenched-tempered specimens.
    (4) Change of the wear resistance resulting from change of hardness was more remarkable in low hardness alloy than in high hardness alloy.
    (5) In the alloy including large amount of vanadium-carbide, the wear resistance scarcely changed by heat treatment.
  • Production Process of Large Forging Ingots

    pp. 1771-1787

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  • The Current Status on Energy Problem and the Strategy of Energy Conservation in Japan

    pp. 1788-1793

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  • 誌上討論

    pp. 1797-1799

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  • 抄録

    pp. 1800-1805

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    Readers Who Read This Article Also Read

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