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

Tetsu-to-Hagané Vol. 59 (1973), No. 12

  • 技術の基本

    pp. 1485-1486

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  • First YUKAWA Memorial Lecture

    pp. 1487-1496

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  • Rate of Hydrogen Reduction of an Iron Oxide Pellet under Pulsating Flow

    pp. 1497-1505

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    In order to examine the effect of pulsating flow on the reduction kinetics, a single iron oxide pellet was reduced with hydrogen under pulsating flow in the temperature range of 500°C-1100°C and in the frequency range of 3.3-43.3 Hz. Three kinds of apparatus were employed to generate pulsating flow i.e. butterfly valve, rotary cock, and piston.
    The rate of reduction was markedly accelerated by pulsating flow under the condition of a small flow rate of hydrogen.
    After analysing the experimental results by the shrinking core model, it was found that the mass transfer coefficient in the gas film under pulsating flow was increased compared with that under steady flow.
    The effect of pulsating flow on kinetic parameter such as mass transfer coefficient, intraparticle diffusivity and chemical reaction rate constant was also discussed.
  • On the Top Gas Recycled Reforming Process and the Injected Gas Distribution

    pp. 1506-1522

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    Penetration of the gas injected into blast furnace stack and its influence on iron are reduction was investigated by two and three dimentional cold model experiments and the theoretical consideration to predictit for the commercial furnace. Gas compositions and the coke replacement ratio were also investigatedexperimentally and theoretically when top recycled reforming process-NKG Process-was adopted. Verylow nitrogen content in the injected gas will be possible if newly proposed method can be applied for theabove process.
    (1) Gas penetration into furnace was mainly governed those three factors such as the injected gas ratioto the total gas passing through furnace U/(U+V), the radial eddy diffusion of the gas, and the radial distri-bution of burden.
    (2) Compositions of the top recycled material gas and injected gas can be calculated by fixing U/(U+V) and C/H ratio of reformed hydro carbon.
    (3) The top recycled material gas and the injected gas containing very low hydrogen can be obtainedby taking out of the top gas periphery of the furnace throat.
    (4) The more amount of reducing gas is injected, the larger coke replacement ratio is predicted by themathematical model calculation. When more than 400 Nm3/tHM of reducing gas is injected, 23 kg/100Nm3 of the coke replacement ratio is expected by taking out of top gas periphery comparing with 17 kg/100Nm3 by the conventional method.
  • On the Decarburization Rate of Molten Stainless by Top-blown Oxygen Gas under Reduced Pressure

    pp. 1523-1539

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    Penetration depth of gas into liquid has been investigated for top-blown lance under reduced pressure. Both theoretical and experimental results show that the depth increases with decrease of pressure, so that a reaction between gas and metal bath is expected to be accelerated by decreasing pressure in gas phase. Decarburization rate has been investigated for 20 kg H.F. furnace with top-blown oxygen gas.
    The rate in the high carbon range is independent on carbon content, but increases with gas flow rate. The activation energy for decarburization rate is determined as 10.9±4.6 kcal/mol at 10 Torr with 1.8 Nl O2/min, which is independent on chromium content from 8 to 17%. The rate controlling step is concluded to be in gas boundary layer.
    Decarburization rate in low carbon range obeys first order reaction of carbon content, and the activation energy is determined as 10.1 and 47.0 kcal/mol at 10 and 50 Torr, respectively. The former is explained through carbon diffusion in the bath, but the latter is not explained without considering oxide effect on the bath surface.
  • Effect of Suction on the Formation of V Segregation in Steel Ingot

    pp. 1540-1549

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    In order to investigate the mechanism of formation of V segregation, molten steel weighing 10 to 20 kg were cast into special shaped sand molds under given conditions influencing upon the occurence mode of V segregation, and observation of macro structure was made on V segregation appearing in each ingots. The mechanism of formation of V segregation was discussed from the observed results. The results obtained were summarized as follows;
    1) V segregation is found to be formed in the so-called accelerated solidification zone by the effect of the suction.
    2) The suction may be defined as the flow of mushy state to feed solidification shrinkage.
    3) The fluidity of mushy state is not so good to fill up easily the solidification shrinkage, so periodical gap might be formed, into which the concentrated melt around them flows.
    4) The velocity of the flow would be greatest at axial center and it decreased near the side wall. Conse quently, the gap become slant to the axis to form V shape.
  • Scanning Electron Microscopic Observation of Fish-eye on the Fatigue Fracture Surface of Surface Hardened Steels

    pp. 1550-1557

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    Fatigue fracture surface, including fish-eyes, of surface hardened steels has been observed with a scanning electron microscope. Near the center of fish-eye, one or more non-metallic inclusions have been found. The results of X-ray micro analysis of the inclusions indicated that the inclusions near the center of fish-eye consist of mainly alumina associating with manganese sulphide, but nosilicate was found in the inclusions.
  • Mechanical Properties of Ausformed Pearlitic and Bainitic Steel

    pp. 1558-1569

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    A study has been performed to clarify the effect of ausforming temperature, ausforming ratio, and subsequent isothermal heating time on the mechanical properties of ausformed pearlitic and bainitic steels. The material used in this study is a high C and Cr tool steel, which has high quench-hardenability. The results obtained are as follows:
    (1) With increases of the working ratio of ausforming and of the holding time at the subsequent transformation temperature, both the hardness and the strength of ausformed pearlitic steel decrease, while the toughness of the steel increases. When the mechanical properties of ausformed pearlitic steel worked at 500°C is compared with that worked at 700°C, the former shows lower values in the hardness and strength and a higher value in the toughness than the latter.
    (2) The ausformed bainitic steel worked with a comparatively heavy ratio shows a fairly good combination of the strength and toughness. On the other hand, the ausformed bainitic steel worked at 320°C is more advantageous in the strength and toughness than that worked at 500°C.
    (3) With an increase of the working ratio of ausforming, both the toughness and strength of the ausformed pearlitic steel worked during the isothermal transformation from austenite to pearlite increase, while the strength of the steel worked above a certain working ratio slightly decreases.
    (4) When the mechanical properties of the ausformed bainitic steel worked during the transformation from austenite to bainite is compared with that worked before transformation, the former shows a higher value in the strength and a lower value in the toughness than the latter.
  • Mechanical Properties of Fe-2atro Ti Alloy Bearing Hydrogen

    pp. 1570-1577

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    Fe-2at% Ti alloys annealed in vacuum and quenched from hydrogen or herium atmosphere at 720°C were pulled in tension between room temperature and -196°C at a strain rate of 1.43×10-4/sec. It was found that at room temperature the yield stress of the alloy quenched from hydrogen atmosphere at 1 atm was approximately twice as that of vacuum annealed one. The yield point behavior and solid solution softening possibility by hydrogen atoms were discussed. A strain-rate cycling test was done in order to obtain the information about the hardening mechanism.
    The yield stress of the alloy quenched from hydrogen atmosphere at 1 atm was decreased rapidly by a low temperature aging process, but the electrical resistivity was increased by the same aging process, and the lattice constant did not change by the aging process at 40°C.
    It may be concluded that iron-titanium-hydrogen alloys are strengthened by Ti-H clusters and that the Ti-H cluster decomposition and hydrogen emission occur by a low temperature aging process.
  • Impact Fracture Characteristics of Cast Irons

    pp. 1578-1591

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    Fracture mechanisms of cast iron under impact loading are not understood so clearly as under static loading. In this study, the instrumented Charpy impact test has been carried out on an annealed grey cast iron with ferrite-pearlite aggregate structure and an annealed nodular cast iron with ferrite structure, and an analysis of impact fracturing behaviour and microfractography on the fractured specimens have been performed.
    Impact values of grey cast iron are not affected by specimen size and notch effects, and these values are not changed by temperature. The fracture process of the grey cast iron can be divided into two stages from the observation of load-deflection curves; i.e., crack-initiation and crack-propagation stages. In the initiation stage, the flaky graphites are cracked and these cracks propagate unstably in the next stage. According to the result of microfractography, cleaved graphite cracks are connected by intergranular fracture and, in some cases, cleavage or tear fracture of ferrite.
    In the nodular cast iron, a transition behaviour with temperature is observed. Especially, in unnotched specimens, this transition is observed clearly and the energy absorbed is mainly occupied by the work for crack-initiation. However, in notched specimens, the impact values are reduced largely and a load-deflection curve of the crack-propagation type is observed. From the result of microfractography, graphite nodules act as a ductile crack nucleating site. At low temperature, however, graphite nodules act as arrester of cleavage crack propagation.
    Further, fracture toughness values of such a low strength brittle material as cast irons are evaluated from the unstable fracture load during impact; these values nearly coincide with the unit crack-propagation energy measured from the area under the load-deflection curve.
  • Determination of Oxygen in Special Steels by the Argon Carrier Coulometric Method with Tin Flux

    pp. 1592-1604

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    The analytical method for the oxygen in special steels has been studied by the argon carrier-coulometry with the addition of Sn metal drops as the bath or flux.
    Since the analytical results often decrease in the order of sample dropping though the temperature and other conditions are held constant, the effects of the properties of graphite crucible and powder on the oxygen values are studied. More accurate and precise values are given by maintaining the, wholeiheating part containing the molten sample at an even high temperature during the operation. When the crucible shape and its position in an induction coil are suitable, the use of graphite material with a large bulk density (d>1.70) and coarse grain is effective to obtain a high temperature. The application to the samples with a large amount of harmful element (Al, Mn, S) gives no interuption under the concentration of 1.6% Al, 3-2% Mn, and 0.5% S, respectively. The determinations of oxygen in the most kind of special steels in volving Ni base high alloys are performed with a good precision [ex:σ=0.7 ppm for JIS-SKS2 (x=8 ppm), σ=3.6 ppm for JIS-SUS 304 (x=71.7 ppm)] and the values obtained agree with those by the vacuum fusion method.
  • Experimental Simulation of Heat Conduction in the Bottom of Blast Furnace with Electric Conducting Sheet

    pp. 1605-1610

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    The temperature distribution in the blast furnace bottom which is constructed by bricks of different materials has been studied by the electric conducting sheet analogy.
    The electric resistance of the parts of the electric conducting sheet is so adjusted by spraying a dilute solu tion of silver paint, that the electric resistance inversely proportions to the thermal conductivity of the fur nace bottom brick.
    The temperature distributions in the blast furnace bottom are estimated by the equi-electric-potential curves on the electric conducting sheet. These electric conducting sheet analogy experiments are performed for different eroded depths of the hearth bottom. The temperature in the hearth bottom of an operating furnace is measured by a few thermocouples located there. The eroded depth is assumed 1050 mm by the electric conducting sheet analogy with these measured temperatures in the hearth bottom.
    On the other hand, the actual eroded depth of the hearth in the reconstruction of the furnace is found to be 1 100 mm. By this result, the electric conducting sheet analogy experiment is useful for estimating the eroded depth of the hearth bottom when the erosion goes along the equi-temperature curves of the hearth bottom.
    This experiment is applied to other blast furnaces, and it is found that the eroded depth is proportional to the integrated pig iron production per unit hearth area.
  • Acicular Patterns in Austenite Formed from Initial Acicular Structure

    pp. 1611-1613

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    Using a low chromium steel, a work has been done on acicular pattern observed in austenite formed by heating of the steel at 2°C/min with initial acicular structure.
    Detailed metallographic study and electron microprobe analyses have proved that acicular patterns in austenite relate to the image brought by etching due to the segregation of manganese in austenite, caused by the partition of manganese between acicular ferrite and austenite produced during α→γ transforma tion of the steel with acicular structure.
  • Some Aspects of Structural Improvements and Technical Progresses in Japanese Ferroalloy Industry

    pp. 1614-1621

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  • Interfacial Phenomena in Metallurgical Reaction

    pp. 1622-1630

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  • 抄録

    pp. 1631-1637

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