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

Tetsu-to-Hagané Vol. 61 (1975), No. 2

  • 再び一大学人の願い

    pp. 175-176

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  • The Electrochemical Measurement of Standard Free Energies of Formation for Fe2SiO4, Co2SiO4 and Ni2SiO4

    pp. 177-181

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    The standard free energies of formation of Fe2SiO4, Co2SiO4 and Ni2SiO4 were measured in the temperature range from 675° to 1000°C by a galvanic cell method, using 0.85ZrO2. 0.15CaO as electrolyte.
    The formation reactions are
    2FeO (s) + SiO2 (s) = Fe2SiO4 (s), 2CoO (s) + SiO2 (s) =Co2SiO4 (s), and 2NiO (s) + SiO2 (s) = Ni2SiO4 (s) foI whichΔG° Fe2SiO4= -10500± 80+ (4.853± 0.074) T cal/mol,
    ΔG° Co2SiO4= -7270± 40+ (3.062± 0.040) T cal/mol,
    ΔG° Ni2SiO4= -5270± 100+ (2.927± 0.093) T cal/mol
    The accuracy of these measurements was discussed together with the thermochemical data of other investigators.
  • Rate of Degassing from Molten Metal by Inert Gas Flushing

    pp. 182-194

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    A study was made of the rate of oxygen removal from molten silver by inert gas flushing. Argon was blown into the melt through an immersed nozzle of 0.15cm in I.D. and 0.30cm in O. D. The gas flow rate was 0.75-3.33 Ncc/sec. The immersion depth of the nozzle was 1.5-6.5cm. From the rate data, the degassing efficiency of argon was calculated. The efficiency f was very high: f> 0.6 at [O] =0.298% and f>0.95 at [O] =0.49%.
    Based on the assumption that the rate was controlled by one or two of the three rate-controlling steps of gas-and liquid-phase mass transfers and chemical reactions at the bubble-metal interface, various reaction models were developed. The rate data were consistent with the model describing the liquid-phase mass transfer during the bubble formation at the nozzle and the bubble ascent in the melt. From the comparison of the measured and calculated times of bubble formation, it was shown that the mass transfer during bubble formation had a large contribution to the degassing process; e pecially in the range of low oxygen concentration of the melt an equilibrium between the bubble gas and the melt was closely approached before the bubble detached from the nozzle.
  • The Solubilities and Diffusion Coefficients of Nitrogen in the Liquid Iron-Nickel and Iron-Cobalt Alloys at 1600°C

    pp. 195-201

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    Solubilities of nitrogen in the liquid iron-nickel and iron-cobalt alloys at 1 600° were measured by means of two methods: in a Mo-resistance furnace and in a mercury-gap high frequency induction furnace. The results obtained by the two methods were well agreed each other within the accuracy of 3ppm.
    The solubility curve of iron-cobalt showed a good agreement with the data found in the literatures previous workers within the accuracy of experimental' errors. However, the solubility of the nitrogen in the nickel alloys showed a higher value at the nickel rich corner.
    The diffusion coefficients of nitrogen in those alloys were determined by the capillary reservoir method at 1600°C. With increasing the nickel and cobalt concentrations, the diffusion coefficients were slightly increased in comparison with that in the pure iron.
    Based on the pertiment various theories, the diffusion coefficients of some elements in the iron-based alloys were discussed. The diffusion coefficient was well described by a Stokes-Einstein-type equation as follows:
    D=a′·1/η·1/γ2·5
    where a′ is a constant, η the viscosity of iron-alloys and γ the covalent radius of a diffusing element.
  • Effect of Niobium Carbonitride on the Deep Drawability of Low Carbon Niobium Steel Sheets

    pp. 202-213

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    This report deals with the effect of Nb carbonitride precipitation on deep drawability of cold rolledannealed sheets.
    The maximum Lankford value was obtained when Nb/C was 8-12 for the vacuum melted steel sheet.
    The solution and precipitation of Nb carbonitride were examined by chemical analysis; it was found that the carbonitride dissolved in austenite at 1 200-1 300° in only a few minutes in the case of extrmely low-C Nb-steel (C 0.006%, Nb 0.18%), but some part of it remained in the case of low -C Nb-steel (C 0.03%, Nb 0.32%).
    Lankford values after cold rolling and annealing were examined for the both types of specimens. The extremely low-C Nb-steels were not affected by hot rolling conditions but low-C Nb-steel shewed a lower Lankford value when soaking and finishing temperatures were high. This was attributed to the precipitation of fine carbonitride.
  • Structures and Tensile Properties of High Strength Ni-Cr-Mo-V Steels Containing 1-5% Nickel

    pp. 214-228

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    Low carbon Ni-Cr-Mo-V steels containing 1-5% nickel were subjected to isothermal or continuous cooling transformations and tempering, which led to a variety of microstructure. Effects of nickel and carbon on the microstructures and on the tensile properties of these steels were examined by means of the tensile testing, dilatation measurement, X-ray measurement, and optical and electron microscopies.
    An addition of nickel improved the tensile properties, particularly the ductility of the steels with the intermediate transformation products as well as the tempered martensitic structures. However, decrease of carbon content exhibited no appreciable contribution to a balanced improvement in the strength and ductility relationship. An increase of the nickel content was found to shift the transformation rariges of the ferrite and the intermediate products to a lower temperature and to a much longer time, and therefore, resulted in enhanced hardenability.
    The intermediate transformation structure, which mainly consisted of bainite, had a considerably low yield strength ratio and low elongation and reduction of area values. The steels with this structure were in general inferior to those with the tempered martensite. When additional tempering at an appropriate temperature was applied to the steel, the intermediate structure of higher nickel steels had a trend of marked increase in yield strength (ratio) as well as an increase in ductility although the tensile strength was decreased. Most of the intermediate structures were composed of lathlike structure with high density of dislocations and precipitation of carbides, and the tempering caused both the rearrangement of dislocations and the secondary hardening, presumably associated with the molybdenum carbide precipitation which was enhanced by a higher nickel content; this seems to cause an optimum improvement in the conbination of strength and ductility.
  • Effect of Tantalum and Nitrogen on Creep Rupture Strength of 12 Cr-l Mo-0.2 V Steel

    pp. 229-240

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    In order to develope a new steel for a large steam turbine rotor which has higher creep rupture strength than 1Cr-l Mo-0.25V steel, an investigation was carried out on the effects of chemical com- positions, such as tantalum, nitrogen and carbon, and heat treatments on creep rupture strength of12Cr-l Mo-0.2V steel.
    1) The addition of tantalum or nitrogen is effective to increase creep rupture strength. The addition of both elements simultaneously is more effective owing to a fine precipitate of Ta (CxN1-x). The creep rupture strength is related to the addition of these elements, according to the following equation:σRup.=A+αTa%+βN%(Ta: up to 0.2%, N: up to 0.1% in the range of C+N: 0.16-0.2%, A: constant, α and β: coefficient).
    2) The higher austenitizing temperature has also some beneficial effect in obtainning higher short time creep rupture strength, but it's effectiveness is small on long time creep rupture strength. The higher austenitizing temperature results in the decrease in rupture ductility, which is desired for large steam turbine rotor. The optimum austenitizing temperature is found to be 1050° to obtain good creep rupture strength with ductility.
  • Wear Resistance of High Speed Steels Made from Atomized Powders

    pp. 241-250

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    This study is aimed to investigate the wear resistance of high speed steel made from atomized powders. The specimens for wear test were prepared by canning extrusion of the SKH9 steel powders with or without various kinds of carbide or nitride powders. Wear tests were, also, carried out for commercial forged SKH9 steel and commercial isostatically compressed SKH9 steel made from atomized powders. The results are summarized as follows:
    1) At high sliding speed, the high speed steel made from powders shows better wear resistance than the forged high speed steel. But at low sliding speed, no significant differences are found between them.
    2) Addition of TiC, WC, TiN or AlN increases wear resistance of high speed steel at both high and low sliding speeds.
    3) Especially, TiC and TiN are very effective in improving wear resistance.
  • Internal Friction of Iron Cathodically Charged with Hydrogen

    pp. 251-257

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    The internal friction of iron cathodically charged with hydrogen was measured asa function of temperature in the range between -50°C and room temperature by the transverse vibrational mode.
    Five relaxation peaks including hydrogen cold-work peak were found in this temperature region and studies were made of the characteristics of four new peaks, P1, P2, P3 and P4, which appeared at around -60°C, -45°C, -10°C and +3°C at 1KHz, respectively.
    Possible mechanisms for the process responsible for these peaks are proposed as follows;
    P1 Peak: Motion of hydrogen-vacancy complex pinning down dislocations.
    P2 Peak: Reorientation of hydrogen cluster by an applied stress.
    P3 and P4 Peak: Redistribution of hydrogen in the stress field of carbon-vacancy complex by an applied stress.
  • State Analysis of Amount of Nitrogen in Carbon Steel

    pp. 258-265

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    This work, a part of the investigation on the state analysis of steel, was carried out to develop a systematic method for isolation and determination of nitrogen as solid solution, and various nitride precipitates in a low carbon steel. The procedure is as follows:
    The steel sample is connected as an anode and dissolved into 150 ml of 1% NaCl-5% EDTA electrolyte (pH 6) with a current density of 50 mA/cm2 for 3.5 hr. Remove the anode, and the residue is collected into a beaker by making use of methanol and is allowed to stand for 45 min. Filter and wash with methanol.
    Transfer the paper and residue to a beaker, add 100 ml of 2% EDTA solution (pH 5) and shake for 60 m in. Filter and wash with 0.01M EDTA solution and determine nitrogen in cementite from filterate by Distillation-Nessler (photometric) Method.
    Return the paper and residue to the beaker, add 30 ml of HCl (1 to 1) and 2 ml of 30% H2O2 and boil gently for 10 min. Filter and wash with water and determine nitrogen as nitride (A1N) from filterate by Distillation-Nessler (photometric) Method.
    Nitrogen as solid solution and as unstable nitride such as iron and manganese nitride is determined from the electrolyte by Distillation-Titration Method.
  • Analysis of the Factors Affecting the Fracture of the Slab Mill Roll by Electron Fractography

    pp. 266-277

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    Fracture surfaces of the rolls have been examined with an electron microscope in relation to the size of cracks and bending stress at breakage, in order to have a technical aspect for the development of materials for slab mill roll. The results obtained are as follows:
    1. The roll life is increased with the decrease of the proportion of the region of brittle fracture to the fracture surface.
    2. The fatigue strength reduction factor of the slab mill rolls is smaller than 1.5, and the notch sensitivity of cast steels seems to be very small.
    3. Following three types of fractures are found;
    (1) fracture by fatigue crack initiated from heat crack.
    (2) fracture by thermal stress.
    (3) fracture originated at the inner defects introduced during casting.
    (4) fracture originated at the inner defects introduced during overlay welding.
  • Some Problems and New Steels for Hull Plates

    pp. 278-286

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  • 抄録

    pp. 287-292

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