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

Tetsu-to-Hagané Vol. 67 (1981), No. 6

  • Technological Innovation and Related Issues

    pp. 649-660

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  • Fracture Control of Steel Structures

    pp. 661-671

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  • Process Kinetics in Injection Metallurgy

    pp. 672-695

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  • Some Problems on the Grain Boundaries in Steels

    pp. 696-702

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  • Technological Forecasting Methods

    pp. 703-709

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  • Finite Element Methods for Analysis of Metal Forming Processes

    pp. 710-719

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  • Some Applications of Boundary Element Method for Two Dimensional Elasticity

    pp. 720-725

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  • Mineral Composition of Dolomite-fluxed Pellets and Its Effect on the Contraction during Reduction up to 1100°C

    pp. 726-735

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    The change in mineral phases during the indurating process was investigated quantitatively for industrially produced dolomite-fluxed pellets and was related to some reducing properties.
    The results obtained are summarized as follows:
    (1) The mineral phases of the pellets consist of hamatite, magnesioferrite-magnetite s. s., calcium ferrite and silicate slag. Calcium ferrite phase melts incongruently at about 1300°C, resulting in increase of liquid slag, and in consequence, the mineral phase bonding iron oxides changes from calcium ferrite to vitreous silicate slag. The contraction during reduction up to 1100°C, which was proved to be closely related to the actual performance of blast furnace, increases abruptly above this temperature. In order to minimize the contraction during reduction, it is important to keep induration temperature just below the decomposition temperature of calcium ferrite.
    (2) The chemical composition of the calcium ferrite solid solution is proposed to be CS-C(F, A)3. It should be noted that this ferrite can solve an appreciable amount of gangue components.
    X-ray precession photographs of this crystal show a c-centered monoclinic pseudo-cell with a-9.979Å, b=15.262Å, c=5.307Å, β=100.23° and a possible space group of C2/c.
    x

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  • Activity of Sulphur in Liquid Iron

    pp. 736-745

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    The equilibrium of sulphur dissolved in liquid iron with the H2-H2S mixture was studied at 1500°-1650°C in a resistance furnace or an induction furnace.
    As the discrepancy was observed among the results obtained by previous reseach groups, the effects of addition of argon to the gas mixture, of the flow rate and the preheating of the gas mixture on the apparent equilibrium constant of the following reaction were checked by applying different heating units:
    H2(g)+S=H2S(g).
    Except heating of metals, the same procedures were applied each for the preparation of the H2-H2S mixture, the flow rate of the gas mixture, and the sampling of liquid iron.
    The results obtained in this study show that a resistance furnace is preferable for the study of this system.
    The results obtained in the resistance furnace are as follows:
    logK(=PH2S/PH2·αs)=-1830/T-1.60±0.009
    ΔG°=8372+7.32T±0.04T (cal/mole).
    The activity coefficient of sulphur dissolved in liquid iron decreases with increase in its concentration, and log f's is expressed by the following equation:
    logf's=(-120/T+0.018)·[%S].
  • Activity of Sulphur in Liquid Iron Alloys

    pp. 746-754

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    The effect of alloying element on the activity coefficient of sulphur in liquid iron has been studied by equilibrating liquid iron alloy with the H2-H2S gas mixture at 1550°C in a resistance furnace.
    The results obtained show that the elements such as C, Al, Si, P, Mo and W increase the activity coefficient of sulphur, while V, Cr and Nb decrease as follows:
    log f CS=0.12[%C] C<3%
    log f A1S=0.041[%Al] Al<7%
    log f S1S=0.075[%Si] Si<7%
    log f PS=0.035[%P] P<9%
    log f VS=-0.019[%V] V<11%
    log f CrS=-0.011[%Cr] Cr<15%
    log f NiS=0.0
    log f NbS=-0.013[%Nb] Nb<12%
    log f MoS=0.0064[%Mo] Mo<20%
    log f WS=0.011[%W] W<15%.
  • Precipitation Behavior of Manganese Sulfide in the Steel Transformed from δ-Ferrite to Austenite after Solidification

    pp. 755-763

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    Three steels with carbon content below 0.04 % and sulfur content of 0.03 % having different manganese contents of 0.3, 0.6 and 1.2 %, respectively, were quenched from various temperatures on cooling subsequent to solidification. The number and volume fraction of manganese sulfides in those steels were measured, and also the relation between the sulfide distridution and microsegregation was examined in a 1 % Mo steel. Through these experiments, the precipitation behavior of sulfides in the steels which transformed from δ-ferrite to austenite after the completion of solidification was investigated.
    The results were as follows :
    (1) Sulfides were grouped into two categories, one crystallized by a eutectic reaction and the other precipitated after solidification. The latter was observed in all steels used in this work, but the former only in the 1.2 % Mn steel.
    (2) The crystallized sulfide, which was typical of colony type sulfides, coarsened remarkably in δ-ferrite, but hardly in austenite.
    (3) A small number of sulfides were precipitated in δ-ferrite, but after δ-γ transformation the number increased steeply.
    (4) The precipitated sulfides were classified into the colony type and non-colony type. The former increased but the latter decreased with increasing cooling rate and decreasing manganese content.
    (5) Most of the precipitated colony type sulfides were observed in the finally solidified region. The distribution of fine non-colony type sulfides was roughly uniform, while that of coarse one concentrated in the solute-enriched region, like the colony type sulfides did.
  • Effect of Alloying Elements and Rolling Conditions on Planar Anisotropy of γ Value of High Strength Hot-rolled Steel Sheet for Deep Drawing

    pp. 764-773

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    Planar anisotropy of γ value (Δγ=|γ090/2-γ45|) of Nb-treated high strength hot-rolled steel sheet is usually high. The way for decreasing Δγ was studied with laboratory melted materials and experimental rolling mill.
    Mechanism which leads to the increase of Δγ can probably be explained as follows: The rolling conditions such as rolling sequence or lubrication may affect the development of austenite texture in a temperature range where recrystallization does not take place. This texture is inherited by ferrite through the γ-α transformation.
    Unidirectional rolling makes Δγ higher than reverse rolling and water-lubrication or no-lubrication makes Δγ higher than oil-lubrication.
    Ti, V, Mo do not have such a strong effect of increasing the lowest temperature of γ recrystallization (Tc) as Nb does.
    So these elements are suitable to the additions for decreasing Δγ of high strength hot-rolled steel sheet for deep drawing.
  • The Effect of Postweld Heat Treatment on Creep Embrittlement of Cr-Mo Steels

    pp. 774-783

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    The effects of PWHT ( Postweld heat treatment ) on creep embrittlement in weldment of Cr-Mo steels for use of boiler and chemical reactor vessels were investigated.
    The correlation among rupture ductility, density and damping capacity was also investigated
    The following results were obtained.
    (1) The rupture ductility of HAZ (heat affected zone) increased with increasing PWHT temperature.
    (2) Intergranular cracking which reduced the ductility was observed under an optical microscope in the earlier period of the secondary creep stage when PWHT had been carried out at lower temperature.
    (3) The creep embrittlement of HAZ generally corresponded with decreasing density and increasing damping capacity.
    (4) The creep embrittlement of HAZ of 1Cr-1/2Mo steel was severer than that for 2 1/4Cr-1Mo steel.
    (5) The service temperature where the severest embrittlement occurred was between 500 and 550 °C for the HAZ of 1Cr-1/2Mo steel and between 550 and 600°C for that of 2 1/4Cr-1Mo steel.
  • Effect of the Grain Boundary Reaction on the Notched Creep Rupture Strength of the Austenitic Heat Resisting Steel

    pp. 784-790

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    An analysis of stress and strain during creep was made on the notched bar specimens of austenitic 21-4N steel by finite element method.
    A decrease in the stress concentration at notch root due to creep deformation occurred more rapidly in the notch-strengthened ductile specimen with 36% of the grain boundary reaction (GBR) than in the notch-weakened brittle one of greater hardness (4%GBR). The equivalent strain at notch root was smaller than that of smooth specimen except in the early stage of creep in the ductile steel, but the former was always larger than the latter in the strongly notch-weakened one.
    In the brittle specimen, an increase in nominal stress enhanced the creep deformation at notch root and consequently lowered rupture time ratio of the notched specimen to the smooth one. Almost of the rupture life was spent in the creep deformation before the initiation of grain boundary cracks in the notched specimen as well as in the smooth specimen, independent of amount of GBR. Amount of plastic deformation necessary to initiate cracks was larger in the ductile specimen than in the brittle one. This is considered to greatly affect the rupture life of the notched specimen.
  • Effect of Alloying Elements on the Strength and Toughness of the Ultra-high Strength Maraging Steels

    pp. 791-798

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    As an ultra-high strength maraging steel which possesses the tensile strength of more than 2400 MPa, the 13Ni-15Co-10Mo steel is well known. However, it necessitates special treatments such as controlled rolling and repetition of rapid heating and cooling to improve ductility and toughness.
    Systematic investigations regarding to the effect of alloying elements on the tensile strength and toughness of ultra-high strength maraging steels are hardly known.
    For these reasons, effect of alloying elements, retained austenite and undissolved precipitates on the strength and toughness within the tensile strength range from 2000 MPa to 3000 MPa were investigated. Results are as follows.
    1) Relation between the tensile strength and toughness was strongly dependent on the combination of the amount of Ni and Mo.
    (a) Ni improved toughness remarkably.
    (b) Mo increased tensile strength strongly without drastic decrease of toughness below 8%.
    2) Ni and Mo definitely decreased Ms temperature. Decrease of tensile strength after aging due to the formation of retained austenite occured when the Ms temperature decreased below 140°C.
    3) Excess addition of Mo increased the solution treatment temperature to dissolve the precipitates, and this made the austenite grain size coarse and decreased the toughness.
    4) The 17.5Ni-6Mo steel was selected as the steel which showed the most suitable combination of strength and toughness.
  • Change in the Texture of Low Carbon Sheet Steel by Intercritical Annealing

    pp. 799-808

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    The effect of the volume fraction of γ phase on texture development has been investigated by making use of several extra low carbon sheet steels which were intercritically annealed in alpha plus gamma dual phase region. The results obtained are summarized in the following. (1) The texture with {111}component developed with increase in volume fraction of γ phase. The intensity of this compoment had two maxima; first at the γ fraction of less than 50% and second at the fraction of more than 60%. (2) The same behavior as (1) was obtained between the Lankford value and γ fraction. (3) The ratio of the {111} intensity of annealed sheet to that of cold rolled one was larger for a thinner specimen than for a thicker one, and also larger for surface layer than for midsection. (4) During slow cooling after intercritical annealing, {111} increased but {100} decreased in intensity. (5) In the residual α phase, {111} intensity increased with increase in γ fraction, and became maximum at 6090% γ phase transformed. (6) Those results were reasonably explained by the new theory on the formation mechanism of the α→γ→α transformation texture, which was proposed by the present authors.
  • An Analytical System for Measuring Continuously Concentration of Trace Amounts of Nitrite and Nitrate Ions in the Activated Sludge Aeration Bath for Ammonia Liquor Treatment

    pp. 809-817

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    A new analytical system for measuring continuously concentration of trace amounts of nitrite and nitrate ions in the activated sludge aeration bath for treatment of ammonia liquor discharged from coke oven, has been developed. The developed system is based on the principle that nitrite and nitrate ions are spectrophotometrically determined at 355 nm and 302 nm, respectively, in the ultraviolet region after elimination of co-existing activated sludge and interferring materials. The proposed system are performed as follows: Sample solution taken from the aeration bath is subjected to centrifugal separation to eliminate the co-existing sludge. And then supernatant solution is passed through activated charcoal column to remove interferring colored materials. Subsequently, the solution is passed through anion exchange column for concentrating nitrite and nitrate ions. The both ions eluted separately from the anion exchange column by sodium chloride solution, are spectrophotometrically determined by ultraviolet detector. Down to 0.1 ppm and 1 ppm of nitrite and nitrate ions, respectively, can be simultaneously measured. The analytical results are automatically given once in every 10 minutes. The results agree well with those obtained by the manual method. The developed system is well applied to the ammonia liquor treatment process.
  • Development of Pure Oxygen Converter and a Patent Issue

    pp. 818-821

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    [in Japanese]
    x

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    pp. 822-831

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  • 中国の大型高炉における操業成績/統計/技術貿易の動向(II)産業別の内訳/技術貿易の動向(I)主要国の技術貿易

    pp. 825-825,833

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  • 抄録

    pp. 836-839

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