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

Tetsu-to-Hagané Vol. 60 (1974), No. 5

  • Theoretical Analysis of Sintering Process Relevant to the Maximum Temperature and the Propagation Speed of Heat Wave

    pp. 465-479

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    Two mathematical models are developed to get the useful information with regard to the rational determination of operating conditions of sintering process. The phenomena of drying, heat exchange between gas and solid particles, combustion of coke, decomposition of limestone and fusion of iron are are considered in Model A. In Model B the fusion of iron are and the decomposition of limestone are not involved.
    By the use of these models, numerical simulations regarding the propagation of sintering zone are made. It has been found from the calculated results that since the heat wave reaches to the steady state within a short period, the basic characteristics of the heat waves may be represented by a few variables to be attained under a steady state; i. e., heat front speed, heat behind speed and the maximum temperature of sintering bed.
    Furthermore, the approximate method is proposed to, obtain the analytical solutions concerning three process variables mentioned above on the basis of the operating conditions. Solutions obtained by this method are in satisfactory agreement with the numercal results over the wide range of operating conditions. Since the necessary time for computation based on the approximate method are extremely shorter than the time for the case of the numerical methods, this method may be available for determining the operating conditions in actual process or for optimizing the sintering process.
  • Study of the Reduction Process of Iron Oxide by High Temperature X-ray Apparatus at Low Temperature

    pp. 480-485

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    This study deals with the reduction process hematite and magnetite with CO gas during gradual heating to 800°C. The process is analysed by high temperature X-ray diffraction technique. The main results are as follows;
    1) The mechanism of production and vanishing of vairous products obtained in the CO reduction process of hematite and magnetite ores is clarified;
    2) The wüstite (FeO) is most slowly reduced among the products obtained in the CO reduction process, furthermore, the reduction velosity of FeO obtained by the reduction of magnetite is slower than that of FeO obtained by the reduction of hematite.
    3) It is observed that the number of pore in FeO produced from hematite is larger than that from magnetite. The difference of porosity is considered to be one of factors influencing on the reduction velocity of FeO;
    4) The iron produced by the reduction of FeO consists of α-phase, and subsequently, transformed to γ-phase;
    5) The cementation structure of iron cristal of γ-phase is microscopically observed.
  • Macro-and Micro-Structure of Continuously Cast Slab

    pp. 486-500

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    Macro-and micro-structure of continuously cast slab are studied. Macro-structure is mainly dependent on casting temperature. Because of its high solidification rate, macro-segregation hardly takes place. Macro-structure is composed of columnar dendrite, brached dendrite and equiaxed crystal. Micro-segregation takes place not only between dendrite stem and interdendrite, but also inside and outside of equi-axed crystal. Micro-segregation is causative of center line segregation of continuously cast slab when solute enriched melt is squeezed from interdendrite into cavity which is formed by solidification shrinkage or bulging of solidified shell by ferrostatic pressure.
  • Effect of Manganese and Salfur on Austenite Grain Size and Recrystallized Ferrite Grain Size After Cold Rolling of Low Carbon Steel

    pp. 501-513

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    A study was made of the effect of manganese and sulfur on the austenite grain size and recrystallized ferrite grain size after cold-rolling in hot-rolled 0.035% carbon steels. No element for refining austenite grains, such as aluminium, niobium etc., has been added in the steels, whose compositions were similar to that of rimmed steels for cold strip.
    Manganese and sulfur contents were varied within the range of 0.1 to 0.4% and 0.01 to 0.03% respectively. Decrease of the manganese content or increase of the sulfur content reduced austenite grain size of ASTM No 1-2 to No 7-8 of the hot-rolled steels which was measured after carburizing at 925°C for 6 hr, and raised the austenite grain coarsening temperature. It was found that the hot-rolled steel with densely dispersed fine particles of 100 to 500Å in diameter showed fine austenite grains, but the steel with sparsely dispersed particles showed coarse grains. It was also found that the recrystallized ferrite grains became finer, when the hot-rolled steel which showed fine austenite grains by carburizing at 925°C was cold rolled and fully annealed. It was thus concluded that the refinement of austenite grains as well as recrystallized ferrite grains results from the fine particles precipitated during hot-roll process, most of which could be identified as β type MnS.
  • Effect of Niobium and Heat Treatments on Creep Properties of 15Cr-14Ni Heat Resisting Steels

    pp. 514-524

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    The effects of niobium and heat treatments on the creep and creep-rupture properties of 15Cr-14Ni heat resisting steels and the electron-microscopic observation have been studied. The relationships between creep properties and several structural factors are discussed. The results are as follows;
    In vacuum-melted 15Cr-14Ni steels, the addition of niobium improves the creep and creep-repture strengths but reduces the rupture ductility. In 0.15C-15Cr-14Ni steels containing niobium, the creep and creep-rupture strengths have maxima at some niobium contents, which increase with increasing the solution temperature. At higher niobium contents, the creep and creep-rupture strengths increase with increasing the niobium content. A decrease of the niobium content or an increase of the solution temperature gives a loss of the rupture ducility in these steels. We find that the increment of the creep rupture strength is proportional to the product of {(%C) sol}0.4×(%Nb)
    sol0.4×(n1)0.2×(Dγ)0.4, where (%C) sot and (%Nb) sol are the contents of carbon and niobium in solution, respectively, (n1) is the distribution density of undissolved carbides and (Dγ) is the mean austenite grain diameter after solution treatment. This is explained by the combination of the following factors; the solid-solution hardening effects by carbon and niobium, the dispersion strengthening effects by carbides, M23C6 and NbC, and the effect of the grain size.
  • Formation of ε Phase in Fe-Mn Alloys Under High Pressure and Its Stability Under Tensile Stress

    pp. 525-539

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    The AS and MS temperature in the martensitic transformation of Fe-Mn alloys under hydrostatic pressures up to 35.5 kbar were measured by the differential thermal analysis. The progresses of γ→ε and ε→α transformation as influenced by the pressure and temperature changes and the effect of the tensile stress on them were discussed from a thermodynamical point of view. The main results obtained are as follows:
    1) The As and Ms temperatures in the γ→←α transformation of alloys containing 4.8% or 6.76% of Mn, by increasing the pressure, were lowered at an approximate rate of 40°C/10kbar, while those in the γ→←ε transformation of alloys containing 6.76 to 28.24% of Mn were raised at an approximate rate of 40°C/10 kbar
    2) The AS and MS temperatures calculated on the basis of the free energy changes of the phases were in a good agreement with those observed.
    3) The γ→ε transformation progressed rapidly in the vicinity of the MSγ→ε temperature and then gradually with further decreasing the temperature. temperatures calculated on the basis of the free energy changes of the phases were in a good agreement with those observed.
    4) In order to stabilize at the ambient pressure and temperature, the β phase which had been formed by pressurizing, it was required that the MSε→α and the ASε→γ temperatures of the alloy were lower and higher, respectively than the room temperature.
    5) The increase in the tensile strength was obtained only for the specimens in which the ε phase had been formed by pressurizing. The reason for the increase in the strength was explained on the basis of the thermodynamics for the γ→ε transformation under tensile stress.
  • The Relation Between Manganese Sulfides and Rust Initiation at the Surface of Steel Sheets

    pp. 540-548

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    The role of manganese sulfides as inclusions on the rust formation process of the steel sheet was investigated by the microscopic observation and the electrolytic isolation method. The obtained results are as follows.
    (1) The first stage of the rust formation process is the dissolution of α(Mn, Fe) S inclusions into dew water on the steel surface.
    (2) The second stage is the one owing to the oxygen contained in dew water; the manganous ions of the dissolved α(Mn, Fe) S reprecipitate as the fine colloidal particles of γ-Mn2O3 (Mn3O4) in the surround ings of the α(Mn, Fe) S inclusions.
    (3) The third stage is the one in which the fine colloidal γ-Mn2O3 (Mn3O4) particles remarkably absorb water and this accelerates the wet corrosion. The brown rust is thus initiated around the γ-Mn2O3-(Mn3O4) particles.
  • Analysis of Steelmaking Alernative Blast Furnace-LD vs. Electric Furnace

    pp. 549-556

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  • Present Situation and Problems of Refractories for Iron and Steelmaking in Japan

    pp. 557-579

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  • Practical Application of Strain Electrode Methods

    pp. 580-589

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  • 抄録

    pp. 590-598

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