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

Tetsu-to-Hagané Vol. 62 (1976), No. 12

  • 随想

    pp. 1475-1476

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  • The Effect of K2O, Na2O and CaO Addition to Fe2O3 Single Crystal on Its Reduction

    pp. 1477-1484

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    The effect of the presence of K2O, Na2O, and CaO in Fe2O3 on its reduction behavior was investigated.Platelets of Fe2O3 single crystals were prepared by the flux method using Na2B1O7, glass as a flux. The size of the crystals was approx. 3 mm in width and 0.3 mm in thickness. In order to make Fe2O3 react with K2O, Na2O, and CaO, small amounts of Na2CO3, K2CO3 and CaCO3 powders were placed on the flat plane (0001) of Fe2O3 and heated at 1100-1300°C in air. It was confirmed by EPMA that reaction products of those substances were formed on some parts of the (0001) plane of Fe2O3. The Fe2O3, crystals were reduced at 750°C in CO and H2 streams, and surface structures were observed by SEM. The results obtained were as follows. When alkaline metals (as Na2O, K2O) were present in Fe2O3, abnormal swelling took place during reduction. It was considered that the swelling was caused by the net effects of (1) cracking of the crystal at early stage of the reduction (2) fibrous iron formation and (3) carbon deposition on the reduced iron. The fibrous iron formation was also observed in the grain boundary of calcium ferrite.
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  • Gas Flow Patterns and Pressure Profiles in Non-Uniform Packed Beds

    pp. 1485-1492

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    In order to explain the gas flow patterns in nonuniformly packed beds, a theoretical model considering the cross flow effects was developed and exact solutions on gas velocities and pressures were derived
    The model was found to satisfactorily represent the experimental results of the pressure profiles in the bed, verifying the validity of this model. Further, it was confirmed that the considerable cross flow was caused in such beds by the axialy nonuniform flow resistance.
    Even though observed gas flow patterns neighboring the end of the beds would be similar to those calculated from parallel model, the inner gas flow patterns should be appreciably different from predictions by any noncross flow model as the parallel one. So consequently, special attention should be paid to the fact in experimental investigations of gas flow in nonuniform packed beds.
  • The Structure of Molten Alkali-Metal Silicates

    pp. 1493-1502

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    X-ray diffraction measurements were made on the binary silicate systems Li2O-SiO2, Na2O-SiO2, and K2OSiO2 in the molten and glassy states. From these results, the following facts were quantitativel confirmed; X-ray diffraction patterns of alkali metal silicates in the molten state are similar to those in the glassy state. Molten alkali metal silicates mainly consist of SiO1., tetrahedral units up to the present experimental composition range i. e., 60 mol% alkali metal oxides. Namely the structural change in the fundamental units due to the addition of alkali metal oxides is not severe. These SiO4, tetrahedral units, however, distribute randomly with increasing the addition of alkali metal oxides. This is confirmed in the short range order parameter estimated from the pair correlation function.
  • Secondary Cooling Pattern for the Prevention of Surface Cracks of Continuous Casting Slab

    pp. 1503-1512

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    In order to prevent surface defects of a continuous casting slab, the most suitable secondary cooling pattern was developed by means of a theoretical calculation and a laboratory scale experiment on the thermal hysteresis similar to those of continuous casting slabs. Moreover, it was considered that thetrans verse corner cracks could be related to the presence of the precipitates which appeared in crystal grain boundaries.
    1) Transverse corner cracks are caused by the precipitates of MN which can form on the grain boundary in the austenite region at the temperatures in the range of 700 to 950°C. Especially, the A1N formation is accelerated by reheating below 700°C
    2) From the experimental results of roles of secondary cooling patterns and of temperatures at the unbending roll in slabs continuously cast, it is ascertained that the prevention of transverse corner crack is mainly related to the secondary cooling pattern, that is, a good cooling rate is less than 83°C/m in the upper part of continuous casting machine.
    3) The newly-developed spray cooling pattern can also give a reduction in the longitudinal surface cracks.
  • Toughness and Ductility of a Characteristic Structure in Isothermally Transformed Molybdenum Steel

    pp. 1513-1522

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    Tensile and impact properties have been examined on isothermally transformed plain 0.2%C steel and 0.2%C-0.5%Mo steel with particular attention to a characteristic structure formed in a molybdenum steel.
    In a plain carbon steel, ferrite-lamellar pearlite structure is formed over transformation temperatures of 450-680°C, while in a molybdenum steel, divorced pearlite structure with blocky carbides is formed at 600-680°C and bainite structure at 450-550°C.
    Lamellar pearlite structures show increasing tensile strengths and decreasing FATT (fracture appearance transition temperature) with decreasing the lamellar spacing, but ductility in tensile tests and shelf energy in impact tests are remained unaffected. With appearance of divorced pearlite in a molybdenum steel, both tensile and impact properties are markedly impaired; tensile strength, ductility, and shelf energy are lowered and FATT is raised.
    Detailed observations of ductile fracture processes show that void initiation occurs at smaller strains in the divorced pearlite compared to the lamellar pearlite or bainite structure.
    Detrimental effects of the divorced pearlite structure on both impact and tensile properties can be attributed to the large, irregular-shaped carbides in the structure.
  • The Sheet Thickness Dependency of Fracture Toughness in High Strength Steels

    pp. 1523-1531

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    The effect of specimen thickness B on the fracture toughness KC as well as on the shear lip thickness BSL of high strength steels was examined to obtain new models for explaining the thickness dependency of KC, and the influence of tensile properties on the dependency was studied.
    The results obtained are as follows.
    (1) For each steel, KC increases with the increase of B in a smaller thickness range where slant fractures occur. In the middle thickness range, however, where fractures of a slant-flat mix mode occur, KC decreases with the increase of B, and in a larger thickness range where flat fractures predominate, KC gradually decreases to a constant value (plane strain fracture toughness KIC).
    (2) The shear lip thickness BSL decreases with the increase of specimen thickness B in the range of the mix mode fracture.
    (3) The new models proposed in this study can express the thickness dependency of KC relatively well.
    (4) An approximate relation, BSL/B=αβmc holds between BSL/B and the relative plastic zone size βC (=K2C/Bσ2ys, where σys, is yield strength). The exponent m does not much change with materials (m=0.6-1.0), but the coefficient α is dependent on the work hardening exponent n (α≈0.0016/n1.6).
  • Diffusion Layers of Electroplated Nickel on Plane Carbon Steels

    pp. 1532-1539

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    A study has been made of the diffusion behavior of electrodeposited nickel on various plain carbon steels. Influences of carbon contents in the various steels used as substrate, heat treatment temperature and holding time on the structure, composition, hardness are of produced diffusion layer are described.
    The results are summerized as follows;
    1) The diffusion layer is formed even after heat treatment at a comparatively low temperature such as 600°C.
    2) The diffusion occurs by volume diffusion process in the temperature range between 600°C and 800°C, while it occurs by grain boundary diffusion process in the temperature range between 900°C and 1000°C.
    3) Some carbides are observed in the diffusion layer, but the kind and type of carbides were not determined by X-ray diffraction in the all steels tested has a comparatively good resistance against nitric acid, and its hardness is as low as 170 in knoop handness.
  • Corrosion of Nickel-base Heat Resistant Alloys in Simulated VHTR Coolant Helium at very High Temperatures

    pp. 1540-1549

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    A comparative evaluation was made on three commercial nickel-base heat resistant alloys exposed to helium-base atmosphere at 1000°C, which contained several impurities in simulating the helium cooled very high temperature nuclear reactor (VHTR) environment. The choice of alloys was made so that the effect of elements commonly found in commercial alloys were typically examined. The corrosion in helium at 1000°C was characterized by the sharp selection of thermodynamically unstable elements in the oxidizing process and the resultant intergranular penetration and internal oxidation. Ni-Cr-Mo-W type solution hardened alloy such as Hastelloy-X showed comparatively good resistance. The alloy containing Al and Ti such as Inconel-617 suffered adverse effect in contrast to its good resistance to air oxidation. The alloy nominally composed only of noble elements, Ni, Fe and Mo, such as Hastelloy-B showed least apparent corrosion, while suffered internal oxidation due to small amount of active impurities commonly existing in commercial heats. The results were discussed in terms of selection and improvement of alloys for uses in VHTR and the similar systems.
  • Hot Corrosion Behavior of Ni-Cr-W-C Alloys in Impure Helium Gas

    pp. 1550-1559

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    Influence of the minor alloy constituents such as Al, Mn and Si on the hot corrosion behavior of Ni-20Cr-20W-0.07C alloy was studied in 99.995% helium gas at 1 000°C, comparing with that behavior of commercial Ni-base superalloys (Hastelloy X and Inconel 617).
    The low oxidizing potential in the impure helium gas usually causes selective oxidation of these elements and the growth of oxide whiskers on the surface of specimen at elevated temperature.
    The intergranular attack was caused by selective oxidation of Al, Si and Mn. The spalling of oxide film was restrained by addition of Mn and Si, providing tough spinel type oxide film on the surface and ‘Keyes’ on the oxide-matrix interface respectively.
    The amount and the morphology of the oxide whiskers depended on Si and Mn content. More than 0.29% of Si content without Mn always caused the growth of rather thinner whiskers with smooth surface, and the whiskers analyzed by electron diffraction patterns and EPMA to be Cr2O3 containing Si. Mn addition changed the whiskers to thicker ones of spinel type oxide (MnCr2O1) with rough surface.
    On the basis of these results, the optimum content of Al, Mn and Si to minimize the growth of whiskers, the intergranular attack and the spalling of oxide film was discussed.
  • Application of Digital Computer to Emission Spectroscopic Analysis

    pp. 1560-1566

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    Recently, there are the following demands for the analysis word with the intersification of the quality assurance and the cost down.
    1. Improvement of analytical precision, from the quality assurance point of view.
    2. Time reduction for analysis.
    3. Cost down for analysis.
    To satisfy these requirements, the utilization of computer was planned for the treatment of emission spectrochemical analysis data, and TOSFAC (T-40C) was set up.After improvements, the practical and highly efficient equipment was developed. Analysis of the data from emission spectrometer, reproduction, evaluation, transmission, registration of the result, and formation of the daily report were made by this equipment.
  • Analytical Solution of the Longitudinal Distribution of Wind in Sintering Machine

    pp. 1567-1569

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    By classifying the sintering process of ores in some zones (drying, pregeating, combustion, and melting zones), and by assuming the relations of Ui=CiG (x) and ΔPi (x) =Di·Gv(x), and ΔPtot(x)=const., the wind distribution in a s intering machine was found to be described by the following relation.
    This integral equation for G (x) was solved as the following function,
    where 1. is the integration constant.
    The above solution can be used in many theoretical discussions for he sintering process.
  • Recent Progress and Future Innovation of Japanese Iron and Steel Industry

    pp. 1570-1576

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  • Report of the Plant Engineering Committee of the Joint Research Society of ISIJ

    pp. 1577-1586

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  • The Steel Industry in China

    pp. 1587-1590

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  • 民族の発展と資材それにおよぼす技術の役割

    pp. 1591-1592

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  • 抄録

    pp. 1593-1598

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