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

Tetsu-to-Hagané Vol. 71 (1985), No. 11

  • Numerical Flow Analysis in Steelmaking Process

    pp. 1423-1434

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  • Recent Studies on the Interfacial Phenomena in which Marangoni Effect Participates

    pp. 1435-1440

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  • Theory of the d Electrons Alloy Design

    pp. 1441-1451

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  • A Genealogy in Ferrous Metallurgy of Japan

    pp. 1452-1459

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  • Iron Ore Preparation and Blast Furnace Practice in Japan

    pp. 1460-1473

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  • Decreasing Non-metallic Inclusions in Molten Steel by Use of Tundish Heating System in Continuous Casting

    pp. 1474-1481

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    Tundish-heater by utilizing channel type electromagnetic induction heating method has been newly developed to prevent the temperature drop of molten steel in tundish at the start, the end of casting and the ladle change in continuous casting. The effect of tundish-heater on temperature of molten steel and qualities of cast slabs of stainless steels have been investigated.
    The results obtained are as follows:
    1) The degree of the temperature drop of molten steel in tundish without heater at the start of casting is 1020°C, on the contrary that with tundish-heater to be 05°C. Temperature drops at the end of casting and the ladle change can be perfectly prevented.
    2) Number of the subsurface inclusions in stainless steel slabs cast at such unsteady states decreases to 1/41/12 compared with that of slabs cast without heating. Surface and internal qualities of coldrolled sheets are also improved to the level of the sheets cast at steady state.
    3) The strong stirring of molten steel in tundish by electromagnetic force can be considered as one of the effect of removal of large inclusions.
  • An Analysis of Behavior of Slab during Compression Casting in a Continuous Casting Machine

    pp. 1482-1489

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    An analysis has been made on a compression casting method which is used to prevent internal cracks of a slab in an unbending zone of a continuous casting machine. To investigate the behavior of a slab during a compression casting, a numerical calculation method was developed. Using this method, stress and strain in a solidified shell of a slab were calculated and the followings became clear: (1) When compressive forces in the casting direction act on a slab in an unbending zone, mutual effect between unbending forces and compressive forces appears and stress and strain on an inner surface of an upper side shell change from tensile to compressive. (2) Compressive forces and temperature of a slab are found to be the primary parameters affecting the effective behavior of the compression casting. From the results of calculations, construction of the machine applying the compression casting method was also discussed about an arrangement of drive and driven rollers, devices for pressing rollers to a slab, prevention of slip between a slab and rollers and controlling method of revolution of drive and driven rollers.
  • An Experimental Investigation on Characteristics of the New Oscillating-plate Viscometer

    pp. 1490-1496

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    The characteristics of the new oscillating-plate viscometer have been investigated experimentally. The results obtained are as follows : (1) The resonant frequency of plate oscillation decreases with increasing viscosity. (2) The apparatus constant K determined experimentally includes the end and slipping effects. (3) The dimensions of the plate should be determined by referring to empirical relations between ρμ and Δ(≡{(Ea/E)-1} n) for various dimensions of the plate, where ρ is the density, μ the viscosity, Ea the resonant amplitude of plate in air, E the amplitude of plate in a liquid, and n a constant. (4) If the distance between the plate and the wall of vessel is longer than about one wavelength of the wave produced by plate, the effect of reflected wave from the wall can be neglected.
    In conclusion, the theoretical working formula, i.e., ρμ=K{(Ea/E)-1}2, is mostly applicable to viscosity measured by the new viscometer. The empirical relation, i.e., ρμ=K{(Ea/E)-1} n, is eminently suitable for instantaneous and continuous viscosity measurement.
  • Derivation of a Kinetics Model for Solute Carbon during Rapid-cooling in Continuous Annealing Process for Low-carbon, Cold-rolled Sheet Steels

    pp. 1497-1503

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    Continuous annealing process for low-carbon, cold-rolled sheet steels generally consists of annealing, rapid-cooling and over-aging. The rapid-cooling plays a role of increasing the degree of supersaturation of solute carbon to accelerate the carbide precipitation during the following over-aging, which brings anti aging property on the products. Therefore, it is elementally necessary to formulate the behaviour of solute carbon during the rapid-cooling in order to investigate the carbide precipitation kinetics in the whole continuous annealing process.
    In this paper, a simple differential equation has been derived for this purpose by an assumption that ferrite grain boundary is an unique site for carbide precipitation.
    Numerically calculated results are compared with experiments in which solute carbon of variously heat-treated materials is measured by the internal friction method. In the region of slower cooling rate and smaller grain, the calculated results well explain the experimental results involving the effect of grain size. In the opposite region, however, the experimental data on solute carbon are much less than the calculated. This can be understood the generation of carbon complex during the measurement of internal friction from the additional experiments.
    So, it is concluded that the kinetics model is effective to evaluate solute carbon just after the rapid-cooling.
  • Hot Metal Treatment by Using LD Slags

    pp. 1504-1509

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    As a means of utilization of BOF slags, their usability to hot metal treatments in removing phosphorus and sulfur and in recovering manganese and iron was examined.
    In order to avoid the melting point rise due to a decrease in FeO content in the slag, 10 to 40% CaCl2 or CaF2 was added to the slag and it was reacted with the hot metal of 50 g or 4 kg containing 0.1 % P, 0.05% S and 5% C at 1 350°C. The ratio of slag to metal in weight was 1: 10.
    While for desulfurization there was no difference in the effect of slag composition, most effective slag for dephosphorization was the one with 20% addition of CaF2 which achieved 90% degree of dephosphorization and desulfurization in 20 min. Iron and manganese in the slag was recovered by 85-89% and 93-97%, respectively.
    Thus, it was indicated that BOF slags, which are considered as industrial waste can be effectively utilized in hot metal treatments.
  • Relation between Thermal Shock Crack and Stress Intensity Factor, and Behavior of Stretched Zone Width

    pp. 1510-1517

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    Purposes in this study are to estimate validity of linear fracture mechanics for thermal shock cracking and to clarify the behavior of stretched zone width in thermal shock. Thermal shock tests were carried out with carbon steel (S53C). Thermal shock was given by jet water on the fatigue precracked surface.
    The following results were obtained;
    1) At a given temperature, thermal shock crack length can be correlated with the maximum value of stress intensity factor which was caused by unsteady thermal stress(maximum stress intensity factor).
    2) Stretched zone width is proportional to the temperature of crack tip at the time when stress intensity factor becomes maximum. Stretched zone width decreases, as the increase rate of stress intensity factor rises.
    The above was also confirmed by results on a different size test specimen.
  • Intergranular Cracking in 0.5Mo Steel Equipment Used under Longterm Operation in Hydrogen Environment at Elevated Temperatures and Pressures

    pp. 1518-1525

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    Remarkable intergranular cracks and local bubble cavities along grain boundaries were detected in a 0.5 Mo steel channel head of a heat exchanger which had been operated in a hydrodesulfurization unit for nine years under a condition well below the operating limit of NELSON chart. The same kind of intergranular cracks in a 0.5 Mo steel feed line pipe were found at welded areas in a periodical inspection during the shut down maintenance period after operation for fifteen years in a catalytic reforming unit.
    Metallurgical investigation and hydrogen exposure tests at 320 and 400°C under 9.81 MPa (100 kgf/cm2) were performed to manifest the cause of damage occurred in the materials. The as-received channel head steel whose microstructure composed of untempered ferrite and pearlite exhibited high susceptibility to intergranular cracking due to hydrogen attack in such case that only M3C carbide precipitated.
    Heat treatment at 650 to 700°C for stress relief was found to be most desirable for securing resistance to hydrogen attack in such hot-formed 0.5 Mo steels as vessel heads, pipes and its fittings to be used in hydrogen environment at elevated temperatures and pressures.
  • Prediction of Creep-fatigue Life by Use of Creep Rupture Ductility

    pp. 1526-1533

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    It was clarified that tension strain hold reduced creep-fatigue life of many engineering materials in different degrees depending on material, temperature and test duration. However the reduction in the life due to holding for various durations could be correlated to the fraction of intergranular facets on fracture surfaces which was considered to be an index of the damage introduced during strain hold. This fraction of intergranular facets by creep-fatigue failure exhibited a direct relation to the creep rupture ductility of the material tested at the same temperature and for the same creep-fatigue life-time.
    From these results an empirical equation has been derived as follow;
    Δεi/DcNhα=C,
    where Δεi is inelastic strain range, Dc is the creep rupture ductility for the same duration as creep-fatigue life time, Nh is the creep-fatigue life under tension strain hold conditions, and α and C are constants depending on the material and testing temperature. From the equation the life prediction is possible for a given inelastic strain range Δεi if the constants α and C, and Dc are known.
    The value of α was found to be 0.62 and 0.74 for various austenitic stainless steels and NCF800 at 600°C and 700°C, respectively, and 0.69 for 11/4Cr-1/2Mo steel at 600°C. The value of C was found to be 0.50 and 0.59 for various austenitic stainless steels and NCF800 at 600°C and 700°C, respectively, and 0.49 for 11/4Cr-1/2Mo steel at 600°C. The creep rupture ductility Dc is available in the NRIM Creep Data Sheets up to 105 h for multi-heats of many kinds of heat resistant alloys.
  • Effect of Carbon on Hot Ductility of As-cast Low Alloy Steels

    pp. 1534-1541

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    The effect of C on hot ductility of low alloy steels has been studied in view of surface cracking of continuously cast (CC) slabs. As the ductility was not affected by C content in hot tensile test of the reheated specimens, the well-known C dependency of surface cracking susceptibility in CC slabs can be ascribed to the microstructural change during the solidification process. Austenite grain size of as-cast materials was found to depend largely on C content, i.e., the maximum grain size appears in 0.100.15% C region. This can be explained by the higher austenite formation temperature in this C region. Austenite grain growth rapidly occurred after the complete transformation or solidification into γ phase, as the strong pinning effect of the second phase such as σ-ferrite or liquid phase on γ grain boundary migration disappeared. Carbon dependency of γ grain size became more marked with increasing cooling rate up to that of ordinary continuous casting.
    Such coarsening of γ grains enhanced intergranular fracture, resulting in ductility loss inversely proportional to the γ grain size. Uneven surface solidification in the mold due to the peritectic reaction will produce much coarser γ structure because of the local delay of cooling. Surface cracking susceptibility will also be largely accelerated by this mechanism. Carbon range where surface cracking susceptibility was the largest varied with the chemical compositions. This shift can be explained in terms of the effect of alloying elements such as Mn on the peritectic composition.
  • Effect of Heat Treatment on Hydrogen Attack Resistance of 0.5Mo Steels

    pp. 1542-1549

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    In order to evaluate hydrogen attack resistance and to manifest factors contributing to intergranular cracking of 0.5 Mo steels, metallurgical studies were carried out relating to manifestation of the cause of many damage due to hydrogen attack in 0.5 Mo steel heat exchangers, pipes and its fittings which had been used in a hydrogen environment below the operating limit curve shown in the NELSON chart revised in 1983.
    Effects of stress relief heat treatment, normalizing and tempering conditions on susceptibility to intergranular cracking and critical temperatures in methane generation of materials taken from a heat exchanger head and a reactor shell plate were investigated by conducting hydrogen exposure tests at 300 to 440°C under 9.81 MPa (100 kgf/cm2). Identification of carbides in residue extracted from the heat-treated materials was also performed by using X-ray diffraction method.
    It was confirmed that high resistance to intergranular cracking due to hydrogen attack and higher critical temperatures in methane generation could be obtained by elevating temperatures in heat treatment for stress relief and tempering after normalizing, owing to precipitation of such stable carbides as M23C6 and Mo2C. Normalization at temperatures below 950°C and tempering at 625 to 650°C were found to be beneficial for ensuring higher resistance to hydrogen attack of 0.5 Mo steels.
  • Relation between Wet Adhesion of Coated Steel and Stress Changes in Coating Film

    pp. 1550-1559

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    Relation between wet adhesion of coated steel and stress changes in coating film has been investigated. Formation mechanism of ZnO under coating film has also been examined.
    Zn3(PO4)24H2O under coating film dehydrates to Zn3(PO4)22H2O with cathodic electrodeposition (C-ED) baking. In the next place, Zn(OH)2 and Zn(H2PO4)2 are produced as a result of hydrolysis of partial Zn3(PO4)2H2O in water immersion. And then Zn(OH)2 dehydrates easily to ZnO. Formed ZnO weakens remarkably adhesion force between coating film and phosphate film. In the meantime, in C-ED coated steel, very large remaining stress is produced in coating film. The bonding between coating film and phosphate film weakened by the formation of ZnO is easily destroyed by this stress. Futhermore, stress due to expansion of phosphate film is introduced as a result of restoration from Zn(H2PO4)2 to Zn3-(PO4)24H2O in water immersion and then promotes the destruction. Accordingly wet adhesion of C-ED coated steel becomes poor.
    The formation of ZnO and progress of hydrolysis reaction are controlled by Ni in phosphate film, and as the result, phosphate film is stabilized. And then stress due to expansion of phosphate film is not introduced because of the formation of amorphous phosphate film. Consequently phosphate film formed in high Ni++ concentration solution makes good wet adhesion.
  • 鋼のISO規格はいくつある?

    pp. 1568-1568

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