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

Tetsu-to-Hagané Vol. 66 (1980), No. 3

  • Fundamental Study on the Mechanical Behavior of Coke as a Material with Rundomly Distributed Pores

    pp. 307-316

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    A miniature bending test method was developed for measuring mechanical properties of coke with better accuracy. Mechanical properties of formed and conventional cokes at room temperature were measured by this method and the effects of pore on them were investigated, taking statistics into consideration. Deformation of a porous body was analysed by the finite element method combined with Monte Carlo method and an attempt was made to develop a method to estimate Young's modulus of coke matrix.
    The results are as follows.
    1) Linear correlation was found between Young's moduli of cokes and maximum bending stress and a possibility of estimating the strength from the measurements of elastic deformation was shown.
    2) Young's modulus of coke decreased with increasing porosity. The decreasing rate of formed coke was different from that of conventional cokes.
    3) Young's modulus of coke matrix was estimated by the new method from apparent Young's moduli including the effects of pores.
    4) From a new viewpoint a comparison was made between the mechanical properties of formed coke and that of conventional one, using the Young's moduli of coke matrix obtained as above.
  • Studies on Dehydration, Reduction, and Hot Strength of Cement Bonded Cold Pellet

    pp. 317-325

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    The dehydration and reduction behaviour of cement bonded cold pellets and their effects on the cold and hot strength were investigated.
    The results are as follows.
    (1) The dehydration of cement bonded cold pellets begins to proceed at about 320°C and the compressive strength at room temperature decreases remarkably after the dehydration at above 600°C, and it increases after the complete dehydration at 900°C, probably owing to the sintering of materials in the pellets.
    (2) The reduction of cement bonded cold pellets is generally faster than fired pellets at above 900°C because of larger chemical reaction rate constant, which, naturally, depends on the reducibility of raw materials and may be affected by some structural factors peculiar to cold bonding.
    (3) At high temperature, cement bonded cold pellets tend to deform more easily than fired pellets and the highter reduction degree and temperature is, the more remarkable the deformation is. It is necessary to define hot strength taking the deformation into account.
    (4) The hot strength of cement bonded cold pellets partially reduced at 700°C800°C is lower than that of fired pellets, but the difference in the hot strength becomes very little after the complete reduction at 900°C1 000°C.
  • Distribution of MgO in Constituents of Self-fluxed Pellets

    pp. 326-335

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    An investigation on the distribution of MgO in the constituents of the self-fluxed pellets containing MgO was carried out by means of X-ray microanalysis and optical microscopy.
    The results obtained were as follows:
    (1) MgO content in magnetite was not always higher even if the chemical analysis of MgO of the pellets was higher, but depended rather on the FeO content of the pellets. Namely, magnetite contained 12.618.4% MgO and 4.57.0% MgO in the cases of FeO content of 0.271.45% and 2.606.74%, respectively.
    (2) Observed MgO contents in the four phases in the pellets (MgO : 0.36.5%, FeO : 0.276.74%), were as follows : magnetite : 4.518.4%, Ca-ferrite : 0.86.0%, slag : 06.0%, and hematite: 0%.
    (3) The magnetite phase in the self-fluxed pellets used in the blast furnace of Kobe Steel, Ltd. was proved to be a solid solution whose composition range was (Fe0.1Mg0.9)O·Fe2O3(Fe0.4Mg0.6)O·Fe2O3.
  • Reduction Rates of Iron Oxide Pellet with Mixtures of Hydrogen and Carbon Monoxide at High Pressures

    pp. 336-345

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    In order to clarify the reduction behaviour of iron oxide pellets at high pressures, a single iron oxide pellet was experimentally reduced with the mixtures of hydrogen and carbon monoxide at 1 000°C. The results obtained were analized by a mathematical model representing the reduction rate of a single iron oxide pellet with the mixtures at high pressures.
    The reduction rate equation of pellets with the mixtures was derived from the three-interface core model on the basis of following assumptions: the reduction rate may be calculated by summing the reaction due to hydrogen and carbon monoxide with the pellet and these reactions proceed independently. In this model, the rate parameters were determined by the reduction of the pellet with hydrogen or carbon monoxide independently. However, diffusion coefficients were evaluated as binary diffusion of hydrogen and carbon monoxide.
    The calculated reduction curves based on the rate equation were found to be in a relatively good agreement with observed curves over the range of gas concentrations, temperatures, and pressures examined. It was found that the reduction rate equation in the paper could be applied to the analysis of the reduction process with mixtures of hydrogen and carbon monoxide at high pressures.
  • Absorption of Sulfur by Liquid Slags from Gas Phase in the Presence of Liquid Iron under Reducing Atmosphere

    pp. 346-353

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    The rates of sulfur transfer from gas phase to the liquid slags in the presence of liquid iron under reducing atmosphere were studied. In the present work, Ar-H2S gas mixture was introduced over slags as CaO-SiO2 and CaO-SiO2-Al2O3-slags at 1 550°C.
    The results obtained are summarized as follows:
    1) Although the sulfur transfer from Ar-H2S gas mixture to liquid slags is independent of the presence of liquid iron, the rate of sulfur absorption of acidic slags increases gradually as the reduction of silica in those slags proceeds.
    2) When the slags are acidic, it is observed that sulfur transfers into liquid iron through those slags and then returns to slags after the maximum concentrations are attained.
    3) Rate of silicon transfer from slags to liquid iron increases with increasing sulfur absorption of slags from gas phase, because the reaction of sulfur absorption of slag accompanies the consumption of oxygen ions in those slags.
  • Mechanism of Sulfide Shape Control in Continuously Cast HSLA Steel Slabs Treated with Ca and/or RE

    pp. 354-362

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    Solute segregation, and constitution and distribution of inclusions in Ca and/or RE treated continuously cast steel slabs have been investigated as a function of concentrations of Ca, RE, S, and 0. Derivation of an atomic concentration ratio, ACR, of effective Ca or RE to S has been made on the basis of commercial scale experiments. Sulfide shape control is insufficient throughout the slabs at ACR of 0.2 and becomes satisfactory at 0.4 except for center-line segregates. This is in accordance with the previous observation for large ingots. Also, sulfide shape control in the center-line segregates has been found to become insufficient with increasing degree of segregation, because the amount of MnS in the segregates increases with increasing solute segregation ratio. This observation is interpreted quantitatively by the decrease due to the precipitation of CaS and/or RES of concentrations of effective Ca and/or RE in the interdendritic melts in the mushy zone during solidification.
  • Measurements of Magnetic Flux Densities and Joule's Heats Induced in the Laboratory-scale High Frequency Induction Furnace

    pp. 363-371

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    Experimental studies have been carried out in order to examine the applicability of Lavers' model to the electromagnetic fields in the laboratory-scale induction furnace with high frequency.
    The furnace used is made of 14 turn 0.054 m-radius and 0.14 m-height induction coil and power supply with frequency of 9.09 kHz or 480 kHz.
    Magnetic flux densities have been measured under the conditions without load, with a long copper cylinder load, and with a mercury pool load, respectively. These values have been well consistent with Lavers' model.
    Joule's heats have been measured for the following metals : copper, zinc, tin, lead and mercury. These values have been well consistent with the model in the range of r1/δ from 4 to 100, where r1 is the radius of load and δ is the skin depth.
    From these results it is possible to apply Lavers' model to the electromagnetic fields in molten iron in a laboratory-scale induction furnace.
  • Mechanical Properties of Sintered Iron Sheets Containing Reduced Iron Powder with Gangue

    pp. 372-381

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    In order to estimate the possibility of utilization of reduced iron powder produced by a fluidized bed, an examination was made on the effect of gangue minerals in iron are on the mechanical properties of sintered iron sheets which contained various oxides of the gangue. Reduced iron powder was carefully mixed with pure iron powder up to 50%. The mixed powder was sintered at 850°C or 900°C for 1 h in hydrogen after pressing, and then rolled and annealed.
    The effect of gangue oxides dispersed in the sintered iron sheets on the mechanical properties was examined. As the content of oxides in the sheets increased, the yield stress and tensile strength increased, but the elongation decreased. After a high temperature annealing in hydrogen, its elongation was improved because of the decrease of oxygen content in iron sheets, while the strength decreased owing to the reduction of oxides during heat treatment in hydrogen.
    These oxides of gangue minerals in iron are changed into glassy ones during reduction. The oxide layers were found to be parallel to the rolling face in iron sheet. These gangues contained in the sintered iron sheet are effective to increase the tensile strength of the sheets produced at lower temperatures. This is seemed to come from the reason that these oxides are crushed and become to be fine particles in the matrix during the rolling.
  • Nonequilibrium Austenite Phase in Rapidly Quenched Fe-Cr-C Alloys

    pp. 382-389

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    By rapid quenching technique, nonequilibrium austenitic alloys with high strength and hardness have been found in Fe-Cr-C ternary system. This formation region is limited to about 1.02.2 wt%C and 730 wt%Cr. The austenite phase has ultra-fine grains of about 0.2 μm in diameter. Their Vickers hardness, 0.2% proof stress and tensile fracture strength increase with increase in the amounts of C and Cr, and the maximum values attain about 630 DPN, 1 500 MPa and 1 550 MPa, respectively.
    These alloys are so ductile that no crack is observed even after closely contacted bending test. In addition, the changes in microstructure and mechanical properties of the tempered austenitic alloys have been investigated and it has been observed that a large secondary hardening occurs at about 870K due to phase transformation from austenite to equilibrium structure of ferrite and M7C3 pearlite.
    Thus the present alloys may be attractive as a high-strength wire or plate.
  • Effects of Carbon and Phosphorus Additions on the Creep Rupture Properties of 21Cr-12Ni Austenitic Heat Resisting Steels

    pp. 390-399

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    The creep rupture properties of 21Cr-12Ni austenitic heat resisting steels containing various content of carbon and phosphorus have been investigated on the basis of grain- and grain boundary-strengths.
    The addition of phosphorus promotes the homogeneous precipitation of M23C6 carbides inside grains an deceases the minimum creep rate. The strength of grains evaluated by the minimum creep rate depends mainly upon the phosphorus content. On the contrary, the strength of grain boundaries evaluated by the grain boundary configuration depends mainly upon the carbon content.
    The rupture strength of steels having straight boundaries is improved with the increase in phosphorus content owing to the increase in the strength of grains. The phosphorus addition above about 0.25%, however, is not effective to improve the rupture strength because of the poor grain boundary strength of these steels. On the other hand, in the steels having stronger zigzag boundaries, the higher the phosphorus content, the higher the rupture strength. Moreover, the rupture strength of the latter is always higher than that of the former regardless of phosphorus content.
    It is emphasized that the optimum content of carbon and phosphorus should be considered from a point of view of the harmony of grain-and grain boundary-strengths.
  • Effect of Austenite Grain Size on the Hardenability of Eutectoid Steel

    pp. 400-409

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    As a first step to obtain a theoretical prediction of hardenability based upon the theories of phase transformation, the effect of austenite grain size on the hardenability of eutectoid steel is examined.
    The effect of austenite grain size on the isothermal pearlite transformation curves were first measured.
    The obtained results were analysed according to the Cahn's theory and the volume fraction of pearlite can be expressed as X=1-exp(-1.31×10-5×t4/d1.76). This result indicates that the pearlite transformation in the steel in present study procceeds by nucleation and growth and dominant nucleation site is grain edge. Step quenching experiments indicates that additivity rule is almost holds.
    Using these experimental data, the effect of austenite grain size on the ideal critical diameter was calculated as DId 0.22. The relation between the ideal critical diameter and the diameter of the bar having any amount of martensite at the center is also calculated.
  • Effects of Case Depth and Notch Shape on the Rotating Bending Fatigue Properties of Carburized Steel

    pp. 410-417

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    For various kinds of carburized case depths in SCM-21, both smooth specimens and notched specimens with various notch shapes were tested under the rotating bending fatigue to evaluate the fatigue strength properties of carburized steel. The main results obtained are as follows : (1) The maximum value of the crack initiating stress σW1 and of the crack propagating stress σW2, namely, the maximum fatigue strength at 107 cycles, were obtained for notched specimen as well as the maximum fatigue limit σW0 for smooth specimen in the case of the specimen with effective carburized case depth of about 0.91.2 mm, corresponding to 1824% of the half the diameter of the specimen. (2) The existence of the non-propagating crack at 107 cycles was observed in the case of the notched specimens with the notch depth of t≥0.24 mm and the notch root radius of ρ=0.08 mm. (3) The following equation was found to hold between the nominal crack propagating stress at the crack tip σ'2W and the effective crack length leff·σ'nW2·leff=Const.
    The exponent n determined was 7.2 for specimen A, 14 for specimen B and 22 for specimen C. (4) For smooth specimen, the appearance of the fish-eye pattern was observed on the fractured surfaces in the case of the specimen with the effective carburized case about 1.0 mm or less deep, but could not be certainly observed in the case of the craburized case depth exceeding 1.2 mm.
  • Some Problems on Materials Tests in High Temperature Hydrogen Base Gas Mixture

    pp. 418-424

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    Some problems have been examined on materials tests (creep rupture tests and corrosion tests) in high temperature mixture gas of hydrogen (80%H2+15%CO+5%CO2) simulating the reducing gas for direct steel making.
    H2, CO, CO2 and CH4 in the reducing gas interact with each other at eleveted temperature and produce water vapor (H2O) and carbon (soot). Carbon deposited on the walls of retorts and the water condensed at pipings of the lower temperature gas outlet causes blocking of gas flow.
    The gas reactions have been found to be catalyzed by the retort walls, and appropriate selection of the materials for retorts has been found to mitigate the problems caused by water condensation and carbon deposition. Quartz has been recognized to be one of the most promising materials for minimizing the gas reactions. And ceramic coating, namely, BN (born nitride) on the heat resistant superalloy, MO-RE II, has reduced the amounts of water vapor and deposited carbon (sooting) produced by gas reactions and has kept dew points of outlet gas below room temperature.
    The well known emf (thermo-electromotive force) deterioration of Alumel-Chromel thermocouples in the reducing gases at elevated temperatures has been also found to be prevented by the ceramic (BN) coating.
  • Estimation of Heat Exchange Area in Sintering Beds

    pp. 425-426

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    A theoretical analysis was made to determine the temperature gradient in the cooling zone of the heat wave of iron ore sintering. The temperature gradient is strongly dependent on the effective heat exchange area which changes with the fusion of bed material. A simple chart was presented to estimate the heat transfer capacity coefficient hpa from observed cooling rate or vice versa. The coefficient hpa and the corresponding effective grain size were estimated from the observed temperature gradients reported in the literature.
  • 自動設計雑談/日本におけるねじの起源

    pp. 430-437

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  • 抄録

    pp. 444-447

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