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

Tetsu-to-Hagané Vol. 62 (1976), No. 14

  • Estimation of Quasibinary Interdiffusivities in Multicomponent Slags for Iromaking and Steelmaking

    Kazuhiro NAGATA, Kazuhiro S. GOTO

    pp. 1777-1786

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    Abstract

    The quasibinary interdiffusivities of CaO-SiO2, Al2O3-SiO2 and CaO-Al2O3 in the CaO-SiO2-Al2O3 liquid slag and those of CaO-SiO2, FeO-SiO2 and CaO-FeO in the CaO-SiO2-FeO liquid slag which is in equilibrium with iron at 1 500°C have been calculated by means of the following equation for cationic conductor;. The cationic tracer diffusivities, in the all range of liquid composition of the both slag systems have been estimated from the relation between the viscosity and the tracer diffusivity.
    The order of the quasibinary interdiffusivities in CaO-SiO2-Al2O3 and CaO-Si02-FeO slags are 10-7 and 10-6cm2/sec at 1 500°C, respectively.The quasibinary interdiffusivities at 1600°C are 2.5 and 1.5 times as much as those at 1 500°C for the blast furnace type slag and the steelmaking type slag, respectively. The accuracies are about ±0.5 and ±1.0 in common logarithms, respectively.
    The ways to use the quasibinary interdiffusivities for the practical problems have been discussed.

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  • Reaction Kinetics of Silica Reduction by Aluminium in Liquid Iron

    Takashi SASAI, Rokuro SAKAGAMI

    pp. 1787-1794

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    Abstract

    Experimental results are given for the rate of reduction of silica after aluminiumaddition to iron melt, which contains about 0.07% silicon and is in equilibrium with silica crucible at 1600°C and 1635°C.
    The whole process of reaction after aluminium addition is divided into four periods, in which the following material balances hold,
    1st period 2ΔO=4ΔSi+3ΔAl 2nd period 4ΔSi+3ΔAl=0
    3rd period 2ΔO=3ΔSi+4ΔAl 4th period ΔO=2ΔSi
    and within the 2nd period, silicon and aluminium contents of iron melts change linearly with time and oxygen contents of them are kept constant.
    It is shown that the adsorption of oxygen to the crucible-melt interface is the rate-controlling process in the reduction of silica. On the assumption that the reaction proceeds steadily through the 1st and the 2nd periods, the rate constant and the activation energy of oxygen adsorption and changes of the dissolved oxygen contents within the 1st period are obtained.

  • The Characteristics of the Oxygen Jet in the Vacuum Refining Process

    Yoshio KOTANI, Takami IKEDA, Kazuo ISHIHARA

    pp. 1795-1802

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    Abstract

    In order to find suitable lance to blow oxygen stably at the vacuum refining of stainless steels, the total pressure of oxygen jet ejected into vacuum from various kinds of nozzles were investigated and the following results were obtained:
    (1) The total pressure of jet from the pipe, which is used as oxygen lance ordinarily, is comparatively low, and this tendency becomes remarkable especially at low vessel pressure.
    (2) By using the Laval nozzle which is designed by Mach number corresponding correctly to the vessel pressure, it becomes possible to increase remarkably the total pressure of jet.
    (3) It is possible to keep the total pressure of jet high by using such a Laval nozzle that becomes insufficiently divergent when the vessel pressure decreases during the refining.
    By applying the Laval nozzle designed on the bases of these results to the 50t ladle furnace, it became possible to blow oxygen from the lance height more than twice of that from the pipe. Accordingly, as the erosion of oxygen lance can be prevented, the refining process becomestable remarkably.

  • Origin and Removal of Large Nonmetallic Inclusions Occurring during Continuous Casting of Wide Slabs

    Yasuhiro HABU, Hidenari KITAOKA, Yutaka Yoshii, Toshihiko EMI, Yoshiharu IIDA, Tunehiro UEDA

    pp. 1803-1812

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    Abstract

    Contribution of tundish slag entrainment, reoxidation, and refractory errosion, to the amount of large nonmetallic inclusions occurring during teeming in continuously cast slabs has been determined with tundishes of varying design equipped with different type of nozzles. Reoxidation taking place during teeming from ladle to tundish, travelling in tundish, and teeming through tundish nozzle, has also been evaluated separately. The fraction of large inclusions occurring from the entrainment of tundish-or mould-slag has been examined by use of La2O3 or CeO2 as tracer. Most of large inclusions has been found to be of exogenic origin arising mainly from air reoxidation and tundish slag entrainment.
    On the basis of these observations, a combination of specifically designed tundish and tundish nozzle has been developed to virtually remove inclusion accumulation in the upper quarter thickness of continuously cast slabs for deep drawing-ironing strip steel and control-rolled high strength strip steels.

  • On the Formation of Internal Cracks in Continuously Cast Slabs

    Hiromu Fujii, Tetsuro OHASHI, Takeshi HIROMOTO

    pp. 1813-1822

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    Abstract

    In order to understand the mechanisms of internal cracks formation in the continuously cast slabs by a bow type machine in Hirohata works, influences of casting conditions have been surveyed. Metallographic structure near the internal cracks has been investigated, and by means of autoradiography, generation and growth of internal cracks have been estimated. The results obtained are as follows:
    1) As far as the investigated casting conditions are concerned, major cause for the internal cracks is the stress arising from correcting of bulging, which mainly depend on casting speed and specific rate of cooling water. Influences of solute elements are also recognized.
    2) Internal cracks are formed adjacent to the solid-liquid interface, where solute enriched liquid penetrates into the crack in solid phase. As a result of repeating the above phenomena taking place by the correcting of bulging, internal cracks are considered to grow gradually.

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  • Alteration of Refractories of High Frequency Induction Furnace during Steel Refining under Vacuum and/or Atmosphere

    Masataka KAMAKURA, Masaaki TAKAGI, Shigeru MIURA, Eijiro ISHIKAWA

    pp. 1823-1832

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    Abstract

    In the refining of steels with the high frequency induction furnace, some reactions arise between the furnace refractory and molten steel. Then, the high temperature properties of refractory affect on the furnace life.
    In this paper, with the vacuum and atmospheric induction furnace, the alteration of refractories after the melts being charged were studied by the macroscopic and microscopic observations, chemical analysis and X-ray diffraction method. The relation between the alteration of refractories and the refining of the molten steel was also discussed.
    The results were as follows:
    1. The alteration of the furnace refractories was much affected by the atmospheric conditions, the chemical composition of steel melts and the characteristics of refractories such as compound constituent, particle size distribution and casting method.
    2. The deep penetration of the molten steel into the refractory through cracks and the metal deposition on the vacancy in the refractory were observed. These metals gave some alterations in surroundings.
    3. The inner surface of furnace refractory was probably kept in fused or partially fused state, because some complex oxides were produced by the reaction between molten steel and refractory materials.
    4. The thin film of molten steel was spread on the surface of refractories after tapping and oxidized. The alteration of refractories occursed by the chemical reaction with this oxidized film and the diffusion of it.

  • Deformation and Elongation Efficiency of Metals When Rolled in Different Stretching Passes of Square-Flat, Square-Oval, Square-Diamond and Round-Oval

    Yoshihiro SAITO, Mikio MORIGA, Shunji KATO, Shojiro UCHIDA, Kenzo KATO

    pp. 1833-1841

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    Abstract

    In order to improve the production capacity and reduction of rolling energy consumption in breaking down pass sequences of rolling of wire and rod, it is required to employ such pass sequences and rolling conditions that increase elongation per pass and elongation efficiency (fw) defined as a ratio of natural elongation (lnλ) to natural draught (ln λmax) imposed by the pass.
    Influences of main geometrical factors, i.e., pass shape factor (mk) thickness ratio (H1/D0), relative draught and degree of filling of pass (ξ) on the cross section of products and elongation efficiency are investigated for passes mentioned in the title by means of simulative rolling test using white plasticine and model plaster rolls. These simulations are checked by hot rolling of commercial steel.
    The main results obtained are as follows:
    1) A higher value of fw can be obtained in the pass-rolling than in the square-flat rolling only when ξ is sufficiently high. Especially in such passes as square-diamond and round-oval where central zones in stock width get relatively heavy reduction or in passes which have high mk value, fw depends sensitively on ξ.
    2) Limiting coefficient of elongation, λ(1), defined as a maximum permissible coefficient of elongation for a given pass increases by decreasing mk, which tends to lower fw. When H1/D0 is increased, however, λ(1) and fw increases and drop of fw by lowering mk becomes alleviated.

  • The Influence of Hot Rolling and Heat Treatments on the Distribution of Boron in Steel

    Seiichi WATANABE, Hiroo OHTANI, Tatsuro KUNITAKE

    pp. 1842-1850

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    Abstract

    The distribution of boron affected by hot rolling and heat treatments has been studied in an 80kg/mm2 grade high tensile strength steel using the technique of boron autoradiography, which can distinguish boron-rich precipitates (BN) from atomic boron segregated to grain boundaries.
    A much faster velocity of moving grain boundaries due to hot rolling than that of the migration of boron atoms in austenite does not allow boron atoms to follow the moving boundaries to segregate and thus only widely-spread distribution of boron along the deformed boundaries results. Since the velocity of the boundary migration due to recrystallization after hot rolling is not so high as that of the boundary deformation, the boundaries sweeping the matrix may trap the boron atoms which have spread widely along the boundaries before the boundaries sweep. Consequently boron atoms segregate intensively along the austenite grain boundaries after the recrystallization.
    In specimens quenched from 1300°, boron atoms are observed to segregate to austenite grain boundaries but direct observations of thin foils prove no boron-precipitates on the boundaries. Reheating above Ac3 after quenching from 1300°C, boron-rich precipitates (BN) form on the prior austenite grain boundaries. The intensity of fission tracks of those precipitates in low nitrogen (30ppm) steel is much weaker than those in high nitrogen steel. At this stage the segregation of boron to the boundaries of austenite grains formed by reaustenitizing is not observed in high nitrogen steel while it is done in low nitrogen steel.
    Reheating, to 1000°C, the high nitrogen steel containing an adequate amount of Al after quenching from 1300°C results in the reduction of the intensity and density of fission tracks of boron-rich precipitates (BN) and the segregation of boron atoms to the boundaries of austenite grains. Taking the results of previous paper into account, it is considered that heating at 1000°C results in the dissociation of boron precipitates (BN) on the prior austenite grain boundarie3 by the reaction of Al+BN=AIN+B and thus boron segregates austenite grain boundaries.

  • Precipitation Behavior of Boron in High Strength Steel

    Seiichi WATANABE, Hiroo OHTANI

    pp. 1851-1858

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    Abstract

    The hardenability of boron steel is affected by the precipitation behavior of boron. Precipitates in the boron containing steel were studied by extraction replica technique at successive manufacturing steps from hot rolling to heat treatment.
    When steels are hot-rolled after heating at 1300°C for 1hr, changes of boron precipitates with the cooling rate after hot rolling are as follows:
    1) When steels are water quenched (cooling rate of 90000°C/min) after hot rolling, no precipitates can be observed onγ grain boundaries.
    2) When steels are air cooled (cooling rate of 300°C/min) after hot rolling, boron nitride precipitates on γ grain boundary region.
    3) When steels are furnace cooled (cooling rate of 0.67°C/min) after hot rolling, AIN grows radially from BN which has precipitated before the nucleation of AIN. AIN formed on BN in furnace cooling is dendritic.
    By reheating, at a rate of 15°C/min, a specimen which has been water quenched after hot rolling (above mentioned as 1), the following boron precipitates appear depending upon the temperature range:
    1) Below 880°C, M23(CB)6 precipitates and coagulates on prior grain boundaries.
    2) Above 900°C and below about 1000°C, BN appears on prior grain boundary region which has been previously occupied by M23(C, B)6. M23(C, B)6 is no longer observed at this stage.
    3) Heating around 1000°C, AIN which is not dendritic but acicular grows radially from BN. The size of BN diminishes with growth of acicular AIN.
    The formation of AIN on BN is interpreted as a transit from the non-equilibrium to equilibrium state in Al-B-N system in steels.
    According to PEASE, BN (hexagonal close packed) has the same crystal structure as that of graphite. Because BN in steels was revealed to have spherulite morphology such as spherical graphite, it is considered that [00.1] axes of BN are arranged in radial fashion and (00.1) planes are perpendicular to them, by an analogy to the crystal arrangement of spherical graphite. As the growth direction of AIN is [00.1]AIN, it is considered that an orientation relationship of (00.1)BN//(00.1)AIN is satisfied when MN grows on BN.

  • Mechanical Properties of Fe-Ni Alloys Having Microduplex Structures

    Masayoshi YODOGAWA, Minoru TANAKA

    pp. 1859-1868

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    Abstract

    The relationship between structures and mechanical properties of seven materials having microduplex structures consisting of ferrite (α), martensite (α′) and austenite (γ) in Fe-Ni alloys has been studied by means of microscopic observation, tensile test and impact test.
    The strength of the (α+γ) microduplex structures is larger than that expected by the rule of mixture due to the grain refinement. Their ductility at low temperatures is improved remarkably compared with that of α′. The shape of their grains markedly affects their mechanical properties.(α+γ) microduplex structures containing the unstable γ show the maximum strength and large elongation at a 50-50 phase ratio when they are tested at -196°C. Their low temperature toughness is lower than that containing the stable γ. The tensile properties of (α′+γ) duplex structure are almost explained by the rule of mixture. The tensile behavior of (α+γ′) microduplex structures are similar to that of α′.

  • Effect of Working Prestrain on Fracture Toughness of S35C Steel and Evaluation of Brittle Fracture Strength of Table Rollers

    Isao MASAOKA, Iwao TAKASE, Shinzo IKEDA, Ryoichi SASAKI

    pp. 1869-1878

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    Abstract

    The effect of working prestrain on the hardness, microstructure, strength, and fracture toughness of JIS S35C normalized steel has been investigated. The brittle fracture strength of mill working table rollers has also been discussed. The main results are summarized as follows:
    1) The hardness of steel S35C increases with increasing working temperature and reduction in thickness because of work hardening and strain aging, and becomes maximum at a working temperature of about 300°C. The hardness of the surface layer of the table roller, therefore, remarkably increases after a long service.
    2) Increasing the hardness results in an increase in strength, decrease in ductility, and shift of Vcharpy impact transition temperature. Besides, it is found that it deteriorates fracture toughness. The fracture thoughness decreases with increasing reduction in thickness by working. The specimens worked at 300°C show the lowest value.
    3) The critical crack size for brittle fracture of table rollers whose fracture thoughness in the surface is low is calculated using fracture mechanics. The method for preventing the brittle fracture of table rollers is established from these results.

  • Creep Rupture Strength of Several Nickel-Base Superalloys in Impure Helium

    Rikizo WATANABE, Yoshitaka CHIBA

    pp. 1879-1886

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    Abstract

    In order to estimate long-term creep rupture strengths of pre-selected alloys for intermediate heatexchangers of a very high temperature gas cooled reactor, a creep rupture test in impure helium has been conducted with respect to three newly developed nickel-base alloys and Inconel 617 and the result have been discussed in comparison with those in air.
    Solid solution strengthened 16% Cr-20% W-30%Co-Ni alloy and 23%Cr-18%W-Ni alloy indicate almost the same short-term creep rupture strength in helium as that in air. Long-term creep rupture strengths of these alloys in helium, however, seem to be higher than those in air because crack growth is caused only by mechanical stress in helium, while it is accelerated by oxidation following nitriding in air.
    Inconel 617 indicates significantly lower creep rupture strength in helium than that in air. One of the causes is the difference of crack growth mechanism, but a more significant cause should be made clear.
    Precipitation hardened 18%Cr-4%Mo-6%W-10%Co-2%A1-2.5%Ti-Ni alloy gives a slightly lower short-term creep rupture strength in helium than that in air, but the long-term creep rupture strength in helium seems to be higher than that in air.

  • Extensive Understanding of Sheet Steel Properties

    Hiroshi TAKECHI, Taiichi SATO, Matsuo USUDA, Kiyota YOSHIDA

    pp. 1887-1897

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  • Out Look for the Japanese Industry and the Change in the Industrial Structure

    Takeshi UNNO

    pp. 1898-1907

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  • Report of the Refractory Committee of the Joint Research Society of ISIJ

    Toyohiko OHTA

    pp. 1908-1913

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  • 1st JIM International Symposium “New-Aspects of Martensitic Transformation”

    Imao TAMURA

    pp. 1914-1916

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  • 連続焼鈍材の材質に与える焼延高温巻取の効果

    久保寺 治朗, 中岡 一秀, 荒木 健治, 渡辺 馨, 岩瀬 耕二

    pp. 1917-1918

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  • 抄録

    pp. 1919-1925

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  • © 1976 The Iron and Steel Institute of Japan

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