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

Tetsu-to-Hagané Vol. 75 (1989), No. 6

  • Ultra-high Voltage Electron Microscopy and Its Applications to New Research Fields

    pp. 853-863

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    1. 論文の考察って何?/武士の商法・名誉教授のコンサルタント会社は果たして成功するか Tetsu-to-Hagané Vol.75(1989), No.12
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  • R & D and the Use of Coal-Water Mixtures

    pp. 864-868

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  • Recent Developments on the Hard Magnetic Materials

    pp. 869-878

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  • Mechanical Behaviors of Austenitic Steels and Other Alloys in High Magnetic Fields at Cryogenic Temperatures

    pp. 879-886

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  • Functionally Gradient Composits

    pp. 887-893

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  • Strength Characteristics of Carbon Refractories for Blast Furnace

    pp. 894-901

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    Mechanical properties of eight commercial carbon refractories for blast furnace were examined. Test pieces were cut from large carbon blocks. Bending, compressing and diametral-compressing tests at room temperature and bending test at high temperature were carried out.
    Main results are as follows;
    (1)Correlations were obtained between elastic modulus and compressive strength and also between bending strength and compressing strength.
    (2)There is much difference among commercial carbon refractories in the size of latent crack at matrix-aggregate bond. Those which have small latent crack have high bending strength/elastic modulus ratio and have small an-isotropy of bending strength.
    (3)There is variance in bending strength in large carbon block. The variance of bending strength in each carbon block depends on the variance of its porosity.
    (4)At high temperatures, bending strength decreases with the increase of SiO2 contents.
  • Direct Analysis of Silicon in Molten Pig Iron by Inductively Coupled Plasma Emission Spectrometry

    pp. 902-909

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    Direct determination of Si in molten pig iron without sampling has been developed with ultrafine particles (UFP) generation/inductively coupled plasma (ICP) emission spectrometry. At first, analytical conditions for UFP generation with spark discharge method, transportation of UFP and determination of Si in UFP were investigated with block steel samples. Si could be determined as good as those of the conventional spark emission spectrometry.
    On the next stage, the UFP/ICP system was installed at a production site for the direct analysis of molten pig iron. It was found to be very difficult to apply spark discharge as UFP generation source, because graphite carbon which was spitting from molten iron surface interrupted to make normal spark discharge. Ar gas bubbling method was applied as UFP generation source instead of spark discharge method. The iron UFP could be generated by means of injecting Ar gas into molten iron, and they were transported in an Ar gas stream through 40 m of tube to an ICP torch. The analytical results of 0.2 to 1.0% of Si in molten iron agreed with those obtained by the conventional method after sampling. The time required for analysis of one cycle is approximately 80 s. The present method is more suitable for direct analysis of Si in molten iron.
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  • Mechanism of Dust Formation during Decarburization of High Carbon Iron Melt by Oxygen Blowing

    pp. 910-917

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    Characteristics of dust formation during decarburization of iron melt containing carbon(0.704.86%) and manganese (0.211.48%) were studied using a 50kg induction furnace.
    Platinum, having lower vapor pressure even at high temperature, was added in the melt as a tracer to make clear the origin of dusts.
    The results obtained are summarized as follows;
    (1) Though the major dust particles, collected from exhaust gas during decarburization of iron melts containing carbon and manganese by the top-blown oxygen, are smaller than 4μm, they are formed by the combination of fume dust with bublle bursting dust.
    (2) The ratio of bubble bursting dust collected from exhaust gas is higher at higher carbon concentration of melt.
    (3) Concentration of manganese in fume dust depends on the evaporation rate controlled by the processes of both mass transfer in melt and evaporation from free surface.
  • Development of Continuous Colouring Method for Stainless Steels

    pp. 918-925

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    Coloured stainless steel produced by the process of International Nickel Limited is expensive because of low production efficiency. In this paper, a high speed continuous colouring method is described for the cost down of coloured stainless steels.
    For the high speed production, high temperature (100°C) colouring solutions and high electric current densities (2A/dm2) were employed. However irregular colouring occurred by using high temperature solutions. For prevention of this trouble, a liquid seal apparatus was developed, which divided the colouring solution to high and low temperature parts without a partition wall. This apparatus was consisted of two boxes with narrow slit nozzles and high and low temperature parts of the colouring solution were gushed against stainless steel hoop in each temperature part. The use of the high temperature colouring solution still caused non-uniform colouring through the top to end of hoop, because of concentration change of the solution by the evaporation of water and loss of the colouring solution taken out with the hoop. For the restoration, a control method was developed, in which were supplied the amounts of the consumed sulfuric acid and chromic acid and water.
    With using the above restoration method, uniformly coloured stainless steel hoops whose length was about 150 m can be produced.
  • Durability of Various Coated Steels in Sea Water

    pp. 926-932

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    Tar epoxy coating and mortar lining have been utilized for internal protection of steel pipes for sea water. However, these coatings are often damaged by the fouling of marine organisms. Therefore, we made sea immersion test and sea water loop test on inorganic and organic coatings in order to investigate the durability of them. The marine organisms grew on all coatings, but the coatings of high hardness were hardly damaged by marine organisms. Pure-epoxy and polyurethane coatings were the best among the coatings investigated; their properties in impact strength, bending stiffness, electric resistivity and adhesion strength were unchanged after the immersion and loop tests.
  • Modelling of NbC Precipitation Kinetics in Hot Deformed Austenite on Nb Bearing Low Carbon Steels

    pp. 933-940

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    In order to predict microstructure and mechanical properties in hot rolled HSLA steels, a precipitation model of NbC in austenite was developed. The effects of Nb content, prior austenite grain size and condition of deformation on the precipitation kinetics were quantitatively determined by extraction replica.
    The modelling was basically constructed with the classical nucleation and growth theory, and the precipitation fraction was estimated from the supersaturation of Nb in solution. As effects of deformation on precipitation, a strain energy term was added to the driving force of nucleation. The increase in nucleation sites and the enhancement of diffusibity of Nb were expressed as functions of the dislocation density.
    The experimental results concerning the accelaration of precipitation due to strain and the interaction between recrystallization and precipitation were quantitatively explained by the present model.
  • Formation of Transformation Textures and Plastic Anisotropy in Hot-rolled Steel Sheets

    pp. 941-947

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    The effect of hot rolling conditions on transformation textures, Lankford values (r), and earing on deep-drawn cups have been studied using a low-carbon Al-killed steel, a B-bearing mild steel, and a high strength steel containing Ti or Nb. All samples were produced on a commercial hot strip mill. The effect of B and Nb additions on austenite recrystallization behavior was also studied.
    Transformation textures of the various hot-rolled steel sheets were analyzed from the view point of the retardation degree of recrystallization. It was concluded that there were two types of transformation textures. The first one was transformed from unrecrystallized austenite with rolling texture and the other from recrystallized austenite with recrystallization texture.
    The planar anisotropy of r values in the low-carbon Al-killed steel and the B-bearing steel samples decreased at high finishing temperatures even above the Ar3 temperature. This phenomenon was not due to a random orientation, but rather due to the coexistence of orientation which mutually canceled out the individual planar anisotropies.
  • Effect of the Interaction between Carbon and Substitutional Elements on the Deep Drawability and Texture of Cold-rolled Sheet Steels

    pp. 948-955

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    The effect of the interaction between carbon and substitutional elements such as chromium, silicon and phosphorus on the deep drawability of cold-rolled steel sheets was studied.
    Chromium drastically deteriorates the deep drawability with the coexistence of C. This effect is derived from the interaction between C and Cr: this attractive interaction tends to form Cr-C dipole and weakens the orientation selectivity of recrystallization nuclei by inhibiting the dislocation movement. The effect of Cr is similar to that of Mn.
    Silicon and phosphorus keep similar effects on the deep drawability independent of the existence of C. This reflects the absense of attractive interaction between C and Si or P.
    Phosphorus improves the deep drawability in steels containing both C and Mn in the case of annealing by slow heating. This fact is explained by the indirect effect of P that suppresses the interaction of C and Mn.
  • Castability and Anisotropical High Temperature Strength of Directionally Solidified Ni-base Superalloys

    pp. 956-963

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    A ten-year R & D program to develop advanced gas turbines had been carried out by Agency of Industrial Science and Technology, government research institutions, and Engineering Research Association for Gas Turbines. The ultimate thermal efficiency to be attained in a combined cycle plant was 55% (LHV), for which a high pressure turbine was operated at the gas temperature up to 1400°C. One of the elements to bear this burden was the application of new turbin blade materials with columnar grained structure made through directional solidification (DS). A DS alloy TMD-5 was developed in the advanced turbine program in which:
    (1) DS castability experiments were conducted for the alloy development to obtain blades with complex internal channel for cooling, and it was concluded that the γ' precipitate volume should be at about 58% balanced with optimized mechanical properties.
    (2) Various mechanical properties such as tensile strength, creep strength, high cycle and thermal fatigue strength and physical properties of TMD-5 were tested, and found to be superior to those of a commercialy available DS alloy with the equivalent degree of anisotropy.
  • Effect of Aging Heat-treatment Condition on Creep-rupture Strength of Nickel-base Single Crystal Superalloys

    pp. 964-971

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    Creep-rupture strengths and microstructures of two single crystal superalloys, NASAIR100 and CMSX-3, heat-treated at various conditions were investigated. As aging temperature was raised, γ' particles coarsened and its morphology changed as follows; irregular cube→regullar cube→rounded cube→plate. Optimum creep-rupture strength at 1040°C and 760°C was obtained in the specimens in which the initial γ' morphology was regularly cuboidal. The reason was related to the degree of perfection of "rafted" structure during 1040°C creep and to the change in the deformation mechanism from cutting to by-passing model during 760°C creep. The morphological change of γ' particles is strongly influenced by the lattice mismatch between γ and γ' phases, thus the optimum heat-treatment condition varies with alloys. For an alloy with larger absolute value of lattice mismatch, heat-treatment at lower temperature is desirable and for an alloy with smaller one, heat-treatment at higher temperature is available.
  • Effect of Metallurgical Factors on Long Time Creep Rupture Properties of 1Cr-1Mo-1/4V Steel Castings

    pp. 972-979

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    Creep rupture data extending 80000h duration have been obtained from nine castings of Cr-Mo-V steam turbine steel. The data of the nine castings showed a wide range of rupture time at higher stresses and lower temperatures, and also a wide range of rupture ductility at lower stresses and longer rupture times.
    The rupture time variation was found to arise from the differences in fine distribution of V4C3 and high matrix dislocation density. The V4C3 distributions and the dislocation densities of the nine castings became similar one another as stress was reduced and rupture time consequently increased, which corresponded to a narrow range of rupture time at lower stresses and higher temperatures.
    All of the castings showed the rupture ductility falling at longer times, which was associated with a change from transgranular to intergranular fracture due to cavitation. Therefore the rupture ductility behaviour at longer times depended mainly on a susceptibility to cavitation, and the susceptibility was closely connected with segregation of impurities (P, S, Sn, Sb, Cu and As) to grain boundaries. Total amount of the impurities segregated to grain boundaries had a clear correlation with the reduction of area at rupture.
  • Influence of Carbon Content on Strength and Toughness of Controlled-rolled Boron Steel

    pp. 980-987

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    An influence of carbon content on the strength and toughness of Nb-Ti-B steel, which contains 1.5% Mn or 1.7% Mn finish-rolled at 720°C after heating at 1050°C then air-cooled or acceleratedly-cooled, was studied.
    The strength of air-cooled plates after the controlled-rolling increases as carbon content increases at C=0.0010.015%, because ferrite becomes fine and TiC, Nb (C, N) precipitate, then decreases at C=0.0150.048%, because microstructure changes from fine-ferrite to coarse-ferrite+pearlite, then increases again at C=0.0480.170%, because the amount of pearlite increases. The change of microstructure and strength decreasing at C=0.0150.048% results from a decrease of the amount of free boron and free niobium.
    The toughness decreases at C=0.0150.048%, because the number of separation decreases by a decrease of austenite/ferrite transformation temperature.
    The strength and toughness increase, because ferrite becomes fine and pearlite changes to bainite by an increase of manganese.
    The strength of acceleratedly-cooled plates after the controlled-rolling increases monotonously with an increase of carbon. Because the microstructure becomes fine, and the secondary phase changes from pearlite to martensite by the increase of cooling rate.
  • Effects of Aging and Ni on Cryogenic Mechanical Properties of Austenitic Stainless Steels

    pp. 988-995

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    Effects of Ni and aging on strength, ductility and fracture toughness of Fe-0.02C-18Cr-(10-30)Ni alloys were investigated at cryogenic temperatures. The main results are as follows;
    (1) The aging at 973K for 270ks caused M23C6 carbide to precipitate at grain boundary. The precipitates increased with Ni content.
    (2) Tensile strength was affected greatly by Ni content but not by aging because amount of induced α' martensite corresponded to it.
    (3) Yield strength at 4K was lowerd by induced martensitic transformation.
    This trend was enhanced by aging.
    (4) Elongation was explained by Md30. Aging lowered Md30 in metastable steels.
    (5) In fracture toughness test, aging caused intergranular fracture and deteriorated KIC regardless of Ni content though KIC increased with Ni content. Its dependence in metastable steels was much larger than in stable steels. The 15Ni% steel had extremely high KIC because TRIP relaxed stress concentration at crack tip.
    (6) It seemed to be possible to improve 4K fracture toughness of aged steels which included a number of grain boundary precipitate if stress concentration around precipitates was relieved.
  • Effects of Ni, Co, Mo, Ti and Al Contents on the Delayed-failure Susceptibility of Maraging Steels

    pp. 996-1003

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    Effects of alloy compositions on the delayed-failure susceptibility have been studied on Ni-Co-Mo-Ti-Al maraging steels by means of tensile tests with varied strain rates, electron microscopy and fractography.
    The results are as follows: Strengthening only by Ti and/or Al additions causes the enhancement of the delayed-failure susceptibility, while the addition of Mo is effective in suppressing the susceptibility by preventing the harmful precipitation along prior austenite grain boundaries. Co also acts as an inhibiter for the delayed-failure when strengthened by Ti and/or Al and Mo, while the addition of Co is not necessary for the tensile strength below 200kgf/mm2. Ni is most effecitive in suppressing the delayed-failure as well as strengthening.
    A Co-free 18Ni-2Mo-2Ti maraging steel exhibited the tensile strength as high as 200kgf/mm2 and very low delayed-failure susceptibility.
    All fracture surfaces of tensile specimens with high delayed-susceptibility were intergranular at the crack initiation site near the surface of the specimen.

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