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

Tetsu-to-Hagané Vol. 80 (1994), No. 2

  • The Effect of the Pattern of the Cohesive Zone on Silicon Concentration in Molten Metal in the Lower Part of Blast Furnace during Operation

    pp. 89-94

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    At Oita No.2 blast furnace a phenomena in the lower part of the furnace, in particular between the cohesive zone and the raceway, was measured and observed directly with a belly probe and a core probe during operation.
    A quantitative relationship was found between the level and the shape of the cohesive zone and the silicon concentration in the molten metal.
    In the case of an inverse V-shaped cohesive zone, as both inner and outer surfaces of the cohesive zone shifted inwards and downwards, there was a corresponding decrease in the silicon concentration in the molten metal.
    A decrease in the average distance between the inner surface of the cohesive zone and the tuyere by 0.4m caused a decrease in silicon concentration of 0.3%.
    In the case of a W-shaped cohesive zone, compared with that of an inverse V-shaped one, a low silicon concentration was obtained by a decrease in SiO gas generation and silicon transfer into the molten metal, which was mainly due to the relatively low temperature and the high FeO content of materials corresponding to the edge of the raceway.
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  • Effects of MgO Content and Temperature on the Reduction Rate of NiO-MgO Solid Solution by Hydrogen

    pp. 95-100

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    In order to obtain proper reduction conditions of the pellets of NiO-MgO solid solution, some pellets were prepared by the sintering of the NiO powder containing MgO of 0 to 20mol% and reduced by H2 over a temperature range of 873 to 1373K.
    The results were summarized as follows.
    1)The reduction rate of NiO containing MgO was decreased with an increase in MgO content at lower temperature than 1073K. In addition, the reduction mechanism of the pellets changed from the topo-chemical reaction to the homogeneous reaction with an increase in MgO content. However, at higher temperature than 1073K, the reduction rate of NiO containing 2.5mol%MgO was higher than that of pure NiO.
    2)The reduction mechanism of the pellets could be explained by the unreacted core model at higher temperature than 1073K. The chemical reaction rate constant, kc, was decreased with an increase in MgO content, and the activation energies of kc increased with an increase in MgO content. On the other hand, the maximum of the intraparticle diffusion coefficient, De, was obtained at NiO containing 2.5mol%MgO.
    3)The effects of MgO on the reduction rate were discussed, referring results of the reduction rate of the wustite containing MgO.
  • The Evaluation of Gas-Liquid Reaction Rate at Bath Surface by the Gas Adsorption and Desorption Tests

    pp. 101-106

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    The separated estimation of the reaction rate at bath surface (surface reaction) and at Ar bubble interface flotating in the bath (bubble reaction) was achieved by the measurements of gas adsorption and desorption rate. The influence of various factors on the surface reaction rate of gas and liquid reaction under the gas stirring condition was investigated for water and molten steel systems. The following points were clarified :
    1)The ratio of surface reaction rate to the bubble reaction rate for N2-molten steel system is much larger than that forO2-water system.
    2)Most of the surface reaction occurs at the flotating area of Ar gas bubbles at the bath surface (activated surfacearea).
    3)The surface reaction rate increases in propotion to one-second power of Ar gas flow rate and in inverse propotion to two-third power of the pressure. In addition, it is strongly influenced by the gas injection depth.
    4)The surface reaction rate well corresponds to the newly introduced parameter for the N2-molten steel and O2-water system, considering the activated surface area, gas flow rate, pressure and gas injection depth.
  • Rate of SiO2 Inclusion Removal from Molten Cu to Slag under Mechanical Stirring Condition

    pp. 107-112

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    A kinetic study has been made on SiO2 inclusion removal from molten Cu to slag (Li2O-SiO2-Al2O3) under static and mechanical stirring conditions. From optical microscopic observation (×400), it is found that SiO2 inclusions in the metal have spherical shape. The inclusion radius is less than 8.25 μm under the present experimental conditions. The oxygen content which originates from SiO2 inclusions in the metal phase agrees with the total oxygen content reasonably well. Hence, the change in the total oxygen concentration of the metal, [mass%O]T, corresponds to that in the amount of inclusions in the metal. A rate constant of inclusion removal, kO is obtained from the log [mass%O]T-time relation. In the range of the rotation speed of the stirrer in the present experiment, the change in the mechanical stirring condition does not affect the rate of inclusion removal from the metal phase. But the rate of inclusion removal under static condition is lower than that under mechanical stirring condition. The rate constant, ko, increases with increasing the initial oxygen concentration, [mass%O]TO.
  • Effect of the Cooling Rate on Compositions of the Oxides Precipitated during Solidification of Steels

    pp. 113-118

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    Effect of the cooling rate on composition of oxides precipitated during solidification was investigated using Ti deoxidized steel. The composition and size of oxides in the continuously cast steels have been observed and theoretically analyzed.The results obtained are as follows.
    The oxide mainly consists of Ti2O3, Al2O3 and MnO. The composition of oxide whose diameter is less than about 10μm changes with cooling rate during solidification. The Ti2O3 content increases and Al2O3 content decreases with the decrease in the cooling rate. On the other hand, the composition of oxide whose diameter is more than about 10μm does not change with cooling rate. When the size of oxide is smaller, the effect of cooling rate on oxide compositions is remarkable.
    As a result of the theoretical analysis of the oxide behavior during solidification on the basis of a diffusion growth model, it has been found that the increase in the diameter of oxide which grows during solidification is larger when the size of oxide before solidification and the cooling rate during solidification are smaller. The Ti2O3 content increases with the decreases in the diameter of oxide before solidification and in the cooling rate. The theoretically estimated results on the changes in compositions and diameter of oxides during solidification of steel qualitatively agree with the observed results.
  • Improvement of Accuracy of Mathematical Models for Gauge Set-up in Hot Strip Finishing Mills

    pp. 119-124

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    To improve thickness accuracy in hot rolled strips, accurate mathematical set-up models for estimating rolling loads and strip speeds in hot finishing mills are investigated. For the set-up models, equations of deformation resistance, and coefficients of friction are proposed here.
    (1)Uniaxial deformation resistance is measured in compression tests. Dynamic softening, accumulated strain, and other factors are considered in the equation for deformation resistance.
    (2)Coefficients of friction in rolling are estimated from forward slip and distortion of the cross section of hot rolled specimens. The values estimated by these two methods agree with each other. The coefficient of friction is expressed as a function of scale thickness and rolling reduction.
    These equations were put to an actual operation of hot strip finishing mills in Mizushima Works, and accurately predicted rolling loads. As a result, the thickness accuracy in hot rolled strips has been improved.
  • Explosive Shock-Consolidation of High Speed Steel Powders

    pp. 125-130

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    High speed steel powders were explosively shock-consolidated under the conditions, that (1) double tube method for cylindrical rod samples and (2) converging under-water shock wave method for rectangular bar samples.
    In case of the double tube method, excess melting was generated at central region and by the heat generated, many circumferential and transversal cracks were formed. The number of cracks were decreased by the arrangement that small powders were placed at the central region, but some transversal cracks were still generated.
    The converging under-water shock was able to achieve higher and longer pressure duration comparing with the other shock-consolidation techniques, and to give the uniform compression to the powders. Surface melting and intensive deformation of the powders were observed and cracks were fairly decreased in comparison with the case of the double tube geometry.
  • Effects of Hard Shot Peening with Water Jet on Surface Residual Stress Distribution of Carburized Steels

    pp. 131-136

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    It is well known that residual compressive stress is an important factor to fatigue strength of carburized parts for automotive industry etc. A systematic study of effect of hard shot peening conditions using high pressure water jet on the surface residual stress distributions in carburized and nitrized SCM-420 steel with surface retained austenite of 4, 12 and 24 pet has been conducted. As a result, high peak value, 1125 MPa and high integrated mean value of stress distribution of compressive residual stress from surface to 300μ m depth were obtained by hard or high energy shot peening with water jet. These increment were caused by elasto-plastic peening effect of matrix and transformation of retained austenite, especially most effective to the specimen with 4 pct surface retained austenite.
    Effect of 2 step peening on compressive residual stress at most surface was not conspicuous in this study.
  • Effect of Tin Addition on Process of Secondary Recrystallization of Fe-3%Si

    pp. 137-142

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    In order to clarify the effect of tin addition on the secondary recrystallization of Fe-3%Si, the behavior of grain growth during secondarily recrystallizing annealing was investigated by SEM-ECC-ECP method. Tin addition accelerates remarkably (110) [001] -oriented secondary recrystallization. Tin is confirmed to segregate on the grain boundary of the tin-added specimen. The (110) [001] grain is approximately in the Σ 9 coincidence orientation in relation to the {111} <112> grain, close to which the main orientation is located in primary matrix of the specimen. It is considered that the relative migration rate of Σ 9 coincidence boundaries comparing with other ones is increased through the tin segregation.
  • Interface Structure and Adhension of Chromium Carbide Film Formed by (C, Cr) Combined Diffusion Treatment on 2 1/4 Cr-1Mo Alloy Steel

    pp. 143-148

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    In order to form thick and hard chromium carbide film on 2 1/4 Cr-1Mo alloy steel, (C, Cr) combined diffusion treatment which was composed of carburizing treatment and chromizing treatment was proposed. Thick chromium carbide film (>30 μm) could be obtained by selecting carburizing and chromizing conditions. The formed surface was composed of chromium carbide film on the substrate and precipitated chromium carbide particles below the film. Furthermore, the obtained film consisted of fine (about 0.5 μm) Cr23C6 and Cr7C3 particles. The precipitated chromium carbide particles below the film mainly consisted of Cr23C6. The distribution of these Cr23C6 particles gradually decreased in proportion to the distance from the boundary between the film and the substrate. The film showed excellent adhesion to the substrate under thermal cyclic condition from 400°C up to 700°C. It was thought that the chromium carbide film which partly penetrated into the grain boundary of the substrate acted as an anchoring effect and the precipitated chromium carbide particles below the film acted as a thermal expansion relief layer. The obtained film showed high hardness over Hv 1000.
  • Relationship between Room Temperature Creep Behavior and Yield Strength in Austenitic Stainless Steels

    pp. 149-154

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    Room temperature creep behavior has been investigated for nitrogen-strengthened austenitic stainless steels (SUS304N2, SUS317J2), cold-rolled SUS304 and precipitation-hardened austenitic alloy (N280 : 35%Ni-20%Cr-2%Ti-0.5%Al). The relationship between the creep behavior and the 0.2% proof stress (0.2% P.S.) is discussed. At a higher stress above 0.2% P.S., all specimens brought about creep strain decreasing strain rate with time. At a lower stress below 0.2% P.S., creep took place in nitrogen-strengthened steels and cold-rolled ones, but not in N280 alloy. The creep strain depends strongly on the normalized stress (applied stress/0.2% P.S.). Increasing the 0.2% P.S. by any strengthening methods raises the stress at which creep strain can be observed. The creep strain can not be determined only by the normalized stress, and affected by the characteristics of the strengthening methods. Comparing the creep strain at the same normalized stress, the creep strain decreases as a following order : nitrogen-strengthened steels, cold-rolled SUS304 and precipitation-hardened alloy.
    The strain rate dependence of 0.2% P.S. decreases in the same order, It is concluded, therefore, that the less strain rate dependence of 0.2% P.S. can lead to the less creep strain at the same normarized stress.
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  • High-Temperature Oxidation of Pure Titanium in CO2 Atmosphere

    pp. 155-160

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    The oxidation behavior of pure titanium has been investigated in the temperature range of 1000K to 1300K in CO2 or Ar-10%CO2 atmosphere.
    Optical microscopy, electron probe microanalyses and X-ray measurements on the oxide scales formed during oxidation indicated that their structures were nearly independent of temperatures and atmospheres employed;the scale consisting of two layers, external one and internal one, have the rutile structure.
    The parabolic rate laws were confirmed on growth of external scale layer and the permeation depth of oxygens in titanium with the apparent activation energies, 266 and 226k J/mol, respectively. The rate determining diffusion species in these oxidation-processes were discussed.
  • Site Occupancy of Re Atoms in Ni3Al(γ') and γ-γ' Phase Equilibria in Ni-Al-Re Ternary Alloys

    pp. 161-165

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    Alloying behaviour of (rhenium) Re in Ni-based superalloys was investigated experimentally. Firstly, the site preference, of Re Atoms in Ni3Al(γ') which is a main strengthening phase in the superalloys, was determined by the ALCHEMI. Secondly, the partitioning ratios of alloying elements between the γ and the γ' phases, and also the phase stability in a Ni-Al-Re ternary system were examined by the EPMA analysis and the microstructural observation as well. As the result, it was shown that Re atoms located preferably in the Al site with about 5378% occupation fraction in the Ni3Al-2mol% Re compound. The trend of the partitioning of Re atoms into the γ' phase decreased with increasing Re in Ni-Al-Re ternary alloys. In addition, the α-phase which is a Re-rich solid solution, precipitated in the Ni-Al-Re ternary alloys containing more than 2mol% Re.
  • Evaluation of Partitioning Ratios of Re Atoms in Ni-Al-Re-X (X : Cr, Mo, W, Ti, Ta, Nb, Co)Quaternary Alloys

    pp. 166-171

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    In order to examine alloying behaviour of rhenium (Re) and its effect on the properties of Ni-based superalloys, the partitioning ratio of Re atoms between the γ and the γ' phases and also the phase stability were investigated using Ni-Al-Re-X(X : Cr, Mo, W, Ti, Ta, Nb, Co) quaternary alloys. When those elements, X, which occupy preferably either Al sites or both Ni and Al sites in the Ni3Al(γ') compound were added to the Ni-Al-Re ternary alloys, the trend of the partitioning of the Re atoms into the γ phase became considerably high in these alloys. Also, the compositional limit of a γ + γ' two phase region in the phase diagram was found to be 34 (mol%) for X(X : Mo, W, Ta, Nb) and 56 (mol%) for Ti in Ni-Al-Re-X quaternary alloys. The results on the partitioning ratio were analyzed with the alloying vectors.
  • Application of Meso-Fracture Mechanics to Behavior of Micro-Surface Crack via Molecular Dynamic Method

    pp. 172-177

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    The deformation and stress fields near micro surface crack tip in α-iron were simulated by molecular dynamic method. In a low stress level, the stress fields simulated by molecular dynamics were resembled to the solution of linear fracture mechanics. Dislocations were emerged from crack tip and the stress at the crack tip decreased by a shielding effect of emitted dislocation from crack tip. Then, the crack tip has shown an geometric shape by slip deformation. This variation of shape of crack tip seemed to promote the shielding effect. From these results, the micro crack, under a plastic deformation condition, might not be accompanied with a singlar-like stress field, according to such circumstances.
  • Dip-coating of Mo(Si, Al)2 on Mo with an Al-Si Melt

    pp. 178-182

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    The formation of intermetallic compound of Mo(Si, Al)2 on molybdenum for a protective coating of high temperatureoxidation was examined by dip-coating technique using Al-Si liquid which was saturated with Si at the temperature range from 1000K to 1200K. The composition of Mo(Si, Al)2 phase is fixed at Mo(Si0.85, Al0.15)2. The growth kinetics is governed by the interface reaction between Mo and Mo(Si, Al)2. The other intermetallic compound is not observed, whose formation is expected from the phase diagram of the Mo-Si-Al system. The Mo(Si, Al)2 formed on Mo is dense and has an excellent adherence to Mo. The layer of Mo(Si, Al)2 on Mo-wire cracks perpendicular to Mo-Mo(Si, Al)2 interface, and forms radially. Mo(Si, Al)2 forms in layer structure on Mo-plate. The activation energy of formation of Mo(Si, Al)2 is 180 kjmol-1
  • High Performance Machining of Metal-Matrix Composites

    pp. N54-N58

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  • Recent Development of Grain Oriented Silicon Steels

    pp. N59-N64

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