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

Tetsu-to-Hagané Vol. 61 (1975), No. 13

  • 随想

    pp. 2773-2774

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  • A Study of the Reduction of NOx in the Waste Gas from Sinter Plant

    pp. 2775-2783

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    The thermal NOx formed in sintering process has been calculated by a simulation model. The result shows that the amount of thermal NOx in waste gas was about 1/1000 of which from the actual sintering process. To assure of this result experimentally, the sintering test has been carried out exchanging the portion of nitrogen in air to argon, and it was confirmed that NOx in waste gas originated mainly from the nitrogen in coke. It was also proved that the nitrogen in ore was converted to NOx, however, the proportion of it was about 10% on total nitrogen in sinter mixture, so that the denitration of coke are necessary for the reduction of NOx from sinter plant.
    For the purpose of denitration of coke, the high temperature reheating of coke was available and the ratio of denitration was increased with rising temperature. For example, the nitrogen in coke decreased from 0.9% to about 0.2% by a reheating at 1800°C for l hr. With sintering test using this low nitrogen coke, the amount of NOx formed could be diminished to about 30%.
  • Equilibrium between Cerium and Sulphur in Liquid Iron

    pp. 2784-2793

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    Cerium-sulfur equilibrium was studiel by melting Fe-S, Fe-C-S, or Fe-Mn-S alloys in high frequency furnace with subsequent addition of cerium under deoxidized argon. The possible reaction between Ce and crucible material was prevented by lining and sintering of CeS powder (3 mm thickness) on alumina crucible in which the melts were contained. Care was also taken to keep total oxygen in the melt to be less than 10 ppm by adding 0.1% aluminum prior to the addition of Ce.
    The results obtained are:
    1) Precipitates identified as CeS by EPMA indicate that the equilibrium is expressed by CeS (S) =Ce+S.
    2) Equilibrium constant, K=a·aS (a: Henrian activity), and interaction coefficients involved are determined to be
    log K=-20600/T+6.39
    e (Ce) S=-13.6 (1823°K), -9.1 (1873°K), -7.5 (1923°K)
    for T=1823-1923°K and [%Ce] +4.37 [%S] ≤0.16, and
    e (C) Ce=-0.077,
    e (Mn) Ce=0.13
    at 1873°K.
    3) Standard free energy of solution, ΔG0, for Ce (1) =Ce is derived as
    ΔGO=-4900-16.0T
    Disagreement among the data previously reported for the solubility product, K′ = [%Ce] [%S], is interpretable by taking the given dependence of K′ on [%Ce] and [%S] into account.
  • Relation between the Transport or Friction Coefficients of Elementary Ions and the Interdiffusion Coefficients of Neutral Oxide Components in Multicomponent Slags

    pp. 2794-2804

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    Molten slag oxides are considered to be dissociated into single ions and/or ionic polymers. In multicomponent systems, linear relations between the fluxes of the ionic species and their electrochemical potential gradients have been introduced for isothermic and isobaric conditions. Relations among transport (and friction) coefficients of ions and the diffusion coefficient matrix of neutral component oxides have been obtained by using the conditions of the electroneutrality and local thermodynamic equilibrium in the slag. All transport (or friction) coefficients can in principle be experimentally determined regardless of the number of components in the slag. The practical aspects of the derived equations have been discussed with respect to 1) transport coefficients and their relation to tracer diffusion coefficients, 2) the interdiffusion coefficient and its relation to tracer diffusion coefficients in quasibinary slags, with some numerical examples, and 3) an approximate treatment given for the rate of diffusional relaxation processes in multicomponent systems for very short and for very long times. Also, rate equations have been derived for the oxidation of a metal by an oxidizing gas, when the metal is contained in a metal bath covered with a multicomponent slag layer. This equation can be compared with Wagner's equation for the oxidation of pure metals.
  • Deoxidation Control in Continuously Cast Steel Slabs for ERW Pipe Use

    pp. 2805-2818

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    Deoxidation control to minimize the amount of large inclusions in continuously cast steel slabs for ERW pipe use has been investigated in commercial heats.
    The results obtained are summarized as follows:
    1) Care must be taken to deoxidize molten steel with Al at tapping, followed by stirring of molten steel by RH degasser within 20 min, and to control Al content in molten steel in tundish less than 0.005%.
    2) The box type alumina graphite immersion nozzle is observed to be superior in refractory erosion with molten steel and in penetration depth of inclusion into crater to the inverse Y type fused silica nozzle.
    3) Investigations on the formation of large inclusions which cause the defect of ERW pipe, reveal that entrapment of slag and/or flux into steel and enlargement in size by the reaction between FeO, MnO, SiO2 in trapped particles and Al, increase progressively with Al content in molten steel.
  • The Effect of Molybdenum and Heat Treatments on Creep Properties of 15Cr-14Ni Heat Resisting Steels

    pp. 2819-2828

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    The effects of molybdenum and heat treatments on the creep properties and micro-structures of 0.15C-15Cr-14Ni heat resisting steels have been studied. The relationships between creep properties and several structural factors and discussed. The results are as follows:
    The creep rupture strength and creep strength increase with the molybdenum content. Below 1% molybdenum, the creep rupture strength decreases with increasing solution temperature, but over this content it has a maximum at the solution temperature of 1 150°C. It is found that the increment of the creep rupture strength due to molybdenum addition is proportional to the product of { (%C) sol} 0.5× { (%Mo) sol} 0.5× (nI) 0.5× (Dr) 0.5, where (%C) sol and (%Mo) sol are the contents of carbon and molybdenum in austenite matrix, respectively; nI is the distribution density of undissolved carbides and Dr is the mean austenite grain diameter after solution treatment. This is explained by the combination of the following factors; the solid-solution hardening by carbon and molybdenum, the dispersion strengthening by undissolved and precipitated carbides, and the effect of the grain size. Massive, cubic and ribbon-like M23C6 and rod-like M6C were observed in the creep ruptured specimens of these steels.
  • Effects of Small Amount of Vanadium and Niobium on Microstructure and Creep Rupture Strength of 12 Percent Chromium Heat Resisting Steel

    pp. 2829-2838

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    Effects of small addition of vanadium and niobium were investigated in order to improve the creep rupture strength of 12% Cr heat resisting steel. The results are as follows.
    1) The creep rupture strength of 12% Cr heat resisting steel is increased by the addition of small amounts of vanadium and niobium. Additions of vanadium and niobium result in precipitation hardening. Especially, in the case of combined addition of vanadium and niobium, the creep rupture strength is higher than that in the case of individual addition of vanadium or niobium. In the case of individual addition, the creep rupture strength of steel containing niobium is higher than that of steel containing vanadium up to 600°C.
    2) It is observed in an electron microscope that coalescence of precipitated carbide particles are retarded by additions of vanadium and niobium to the steel.
  • The Effect of Mn, Cr, and Ni Additions on the Structure, Strength, and Toughness of Tempered Martensite and Bainite in Low C Steels

    pp. 2839-2851

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    The effect of alloying elements on the structure and the strength-toughness relationship of tempered martensite and bainite have been studied in 0.15%C-0.5%Mo and 0.3%C-0.5%Mo steels by the addition of 1.5-2.5% to Mn, Cr, and Ni.
    Differences in the substructure and the strength-toughness relationship are not large in the tempered martensite when the alloying element is changed. The difference, however, becomes remarkable in the bainite with the increase of the formation temperature, especially in the lower C steels. The results of the comparison among these alloying elements made on the bainite formed at higher ltemperatures can be summarized as follows. The bainite in Ni steels shows the coarsest structure with the coarsest particles of carbide. The bainite in Mn steels is similar to that in Ni steels. The structure of the bainite in Cr steels is the finest and quite different from those in the other steels. As for the toughness of bainite, Ni steels show the best followed by Mn steels, and Cr steel the worst. The size of unit fracture facet of these bainite is almost the same. The hardness of the bainite is rather dependent on the formation temperature than the alloying element.
    It is concluded from these results that the intrinsic toughness affected by the alloying element plays more important role in these transformation products formed at higher temperatures than the factors such as the size of unit fracture facet and carbides which have been considered to be important if the alloying element is the same.
  • Application of Cold Nitric Acid and Cold Nitric Acid-Alcohol Methods to Analysis of Nonmetallic Inclusions in Steel

    pp. 2852-2862

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    An investigation has been made on application of the cold HNO3 and cold HNO3-alcohol methods to analysis of nonmetallic inclusions in steels.
    The results obtained are summarized as follows:
    (1) The changes of natural potential and temperature of the cold HNO3 solution through the reaction with iron depend on the concentration of the cold HNO3.
    According to the behavior of reaction with iron, the cold HNO3 medium may be divided into 3 ranges, namely the high concentration range of (4+1) - (1+1) at-15°--5°C, the medium concentration range of (1+3) - (1+7) at-5°-0°C, and the low concentration range of (1+9) - (1+50) at 0°-5°C.
    (2) The medium concentration range is most suitable for decomposition of Fe3C, and the analytical condition of 200 ml (-5°C) of HNO3 (1+7) has been confirmed to be most recommendable for analysis of nonmetallic inclusions in killed steels (sample taken 1g).
    (3) As compared with the cold HNO3-H2O system, the cold HNO3-alcohol system has some different aspects; the natural potential and the dissolving rate for iron are rather lower, but the low concentration range of the system can be applied even below 0°C without freezing.
  • On Equipments and Operation of Continuous Annealing and Processing Line “CAPL” for Manufacturing Cold Rolled Steel Sheets

    pp. 2863-2876

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    Cold rolled steel strips with deep drawing quality are manufactured economically by the CAPL (Continuous Annealing and Processing Line) after cold rolling. CAPL combines 5 conventional processes of electrolytic cleaning, annealing, cooling, temper rolling and recoiling with inspection into one line. Materials most suited for the purpose are low manganese steels (Mn≤0.25%) with K values of 0-0.15, which are coiled at 670°C or above after hot rolling. The K value is defined as follows:
    (for capped and rimmed steels) K=Mn (%) -55/32. S (%) -55/16. O (%)
    (for killed steels) K=Mn (%) -55/32. S (%)
    These steels are cold rolled to the final thickness and then passed through the CAPL. The heat cycle of the CAPL furnace section consists of one-minute annealing, cooling to over-aging temperature at the rate of 5° to 30°C per second and over-aging at 350° to 450°C for a few minutes. The radius of the overaging chamber hearth roll has to satisfy the following relation;
    d/R=2.02×10-3-1.05×10-3-log (t+1)
    where d: strip thickness (mm), R: radius of hearth roll (mm), t: time during which bending stress occurs (min). The built-in temper mill of CAPL has a new type of work roll changing device which enables the replacement of work rolls in 2 min without the strip having to be cut. With other new devices such as direct strip temperature detector, or strip steering device, it has become possible to combine the above 5 processes organically into one single line to reduce man-power, investment cost, energy consumption and yield loss drastically.
  • Ideal Status of Advancement and Reality of Promising Iron and Steel

    pp. 2877-2881

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  • Progress of Iron and Steelmaking Technology and Modernization of Integrated Works in Japan

    pp. 2882-2891

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  • Activity of Nitrogen in Austenitic Steels

    pp. 2892-2903

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  • 抄録

    pp. 2904-2908

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