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

Tetsu-to-Hagané Vol. 74 (1988), No. 5

  • Current Movements in Molecular Dynamics Study with Regard to Its Application to Materials Science and Engineering

    pp. 753-763

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  • Physical Chemistry of Evaporation and Deposition of Metals, Alloys and Their Compounds

    pp. 764-775

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  • Hydrogen-Defect Interactions and Hydrogen-Induced Embrittlement in Iron and Steel (2)

    pp. 776-785

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    [in Japanese]
  • Abrasive Resistance of Coke Oxidized with CO2 by Use of Rotational Abrasive Disk

    pp. 787-793

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    In order to evaluate the abrasive resistance of coke oxidized with CO2 gas, the rotational abrasive disk was used. The specimens of metallurgical and formed coke were oxidized unidirectionally with gas mixtures like bosh gases. The relation between the abrasive resistance and conversion ratio was studied. The results are summarized as follows:
    1) The abrasive resistances of the bulk and matrix of coke can be evaluated distinctively by the indicies proposed in the present study.
    2) The index proposed to show the abrasive resistance of the bulk coke against the abrasive wear has the linear relation with the conversion ratio.
    3) The abrasive resistance of the bulk of coke decreases extensively with the increase in conversion ratio, while that of matrix does not decrease so much. Therefore, the degradation of coke can be attributed mainly to the decrease in the bulk resistance due to the enlargement of pore.
  • Behavior of Gaseous Reduction of Molten Slag Containing Niobium Oxide

    pp. 794-800

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    The behavior of gaseous reduction of molten slag containing niobium oxide was examined for the purpose of making ferro-niobium alloy of good quality.
    The molten slag containing niobium oxide was reduced in the crucibles made of high purity magnesia or pure iron with H2 gas, CO gas and H2-CO gas mixtures. The results are as follows;
    (1) Iron oxide and P2O5 in the slag were easily reduced with H2 gas while they were slightly reduced with CO gas at 1 450°C.
    (2) The slag elements except FeO, Fe2O3 and P2O5 were scarcely reduced with H2 or CO gas in the temperature range from 1 350 to 1 550°C.
    (3) The reduction of FeO with H2 gas was accelerated by the increase in MgO content in slag.
    (4) The relation between (%FeO) and (%P2O5) in reduced slags is expressed in the following equation:
    (%P2O5)=0.037(%FeO)+ 0.04
  • Smelting Reduction of Sintered Manganese Ore in Stirred Bath

    pp. 801-808

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    Reduction of sintered manganese ore in stirred bath was investigated with a 70 kg scale induction furnace and with a 600 kg scale top and bottom blowing converter.
    (1) The change of total manganese content in slag, (T. Mn) is expressed by a first order rate equation. The rate constant, k1 and final manganese content in slag, ( T. Mn) f are affected by CaO/SiO2 ratio, temperature, manganese content in metal, the amount of coke and the condition of bottom blowing. k1 and (T. Mn) are almost constant with [Mn] over 25%. In such a condition, it is shown by X-ray transmission method that reduction site is limited to the coke-slag boundary.
    (2) Bottom blown oxygen gas accelerates the reoxidation of manganese and dust formation in the present case, contrary to the case of chromium smelting reduction.
    (3) Top blowing oxygen must be blown softly over thick slag layer in order to keep the metal bath away from oxygen jet.
    It is concluded that the smelting reduction with top and bottom blowing converter is applicable to the production of ferromanganese.
  • Phosphorus Distribution between Fe-Cr-C Melts and CaO Bearing Fluxes

    pp. 809-815

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    In view that Fe-Cr-C melts should be dephosphorized preferably by CaO bearing fluxes for economical reasons, the lowest phosphorous content attainable in equilibrium by the treatment was estimated by measuring 1) the GIBBS free energy of formation of CaO·Cr2O3, which determines the maximum oxygen partial pressure and 2) phosphorous distribution between CaO-SiO2-CaF2 fluxes and Fe-Cr-C melts at 1 300°C.
    The results are summarized as follows:
    1) The Gibbs free energy of formation of CaO·Cr2O3 can be expressed by the following equation.
    2Cr(s)+ CaO+ 3/2O2= CaO·Cr2O3
    ΔG°=-1 350 000 + 344 T±10 000 J/mol
    2) For effective dephosphorization of carbon saturated Fe-16%Cr melts the phosphate capacity of the flux must be higher than 1027.
    3) The addition of a small amount of Na2O or BaO to CaO-SiO2-CaF2 fluxes saturated doubly with CaO and 3CaO·SiO2 was observed to increase significantly their dephosphorization capacity.
    4) The interaction parameter ePCr was found to be -0.039 at 1 300°C.
  • Dephosphorization of Fe-Mn-C Alloy with BaCO3

    pp. 816-822

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    Dephosphorization of manganese alloy ([Mn]i: 5-60%, [P]i: 0.1-0.2%) was tested with flux containing various carbonate of basic oxide, by a 70 kg scale experiment.
    (1) Dephosphorization hardly proceeded with flux containing CaCO3. In the case of treatment with flux containing Na2CO3 or Li2CO3, rate of dephosphorization was also low. On the other hand, the rate of dephosphorization with flux containing BaCO3 was comparatively high, and rephosphorization did not occur. So detailed experiments were done with flux containing BaCO3.
    (2) In the case of treatment of high manganese alloy, the rate of dephosphorization was higher without adding BaCl2 than with BaCl2. This result is different from that for high chromium alloy. The reason is that MnO formed reduces the melting temperature of slag.
    (3) The desirable conditions for dephosphorization with BaCO3 were: (i) lower temperature (ii) [%C] a little lower than the saturation value and (iii) preventing contamination by SiO2 and so on in order to keep (%BaO) as high as possible.
    (4) It was effective to control oxygen potential of atmosphere or flux injection in order to make (%MnO) appropriate (20-40%).
    (5) (P)/[P] of 15-20 was expected for dephosphorization of ordinary ferromanganese with BaCO3 at about 1 300°C.
  • Effect of CaO-CaF2 Powder Injection on Steel Desulfurization in Ladle

    pp. 823-830

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    A study was made on the desulfurization rate of steel by CaO-CaF2 powder injected into a 150 t ladle.
    EPMA analysis of suspending particles taken from an Al-Si killed steel melt during powder injection was made, and two types of particles contributing to desulfurization were found. The one formed by coalescense of injected powder with deoxidized Al2O3 particles showed a high sulfur partition ratio of 1 000 to 6 000. The other type of suspending particles formed by coalescense of injected powder with entrained top slag and Al2O3 showed a lower sulfur partition ratio. Observed sulfur partition ratios of both types of particles agree with those estimated from thermodynamic calculation, which indicates that the reaction between suspending particles and sulfur in a steel melt is in equilibrium.
    A model was proposed, which took account of resulfurization from top slag. Calculation based on the model shows that the contribution of transitory reaction to overall amount of desulfurization is approximately 46% under this experimental condition.
    x

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  • Evaporation Phenomena at the Hot Spot of Oxygen Jet in BOF Process

    pp. 831-838

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    By the measurements of radiation temperature of the hot spot of oxygen jet and by the calculation of the radiation coefficient in the field of vision of single-hole oxygen nozzle, definition of the "luminous radiation temperature" is made as the temperature of the hot spot of oxygen jet ejected onto the molten steel bath surface in BOF process. The luminous radiation temperature thus obtained is ranged from 2 000 to 2 600°C. Evaporation phenomena of iron at the hot spot are calculated following to the HERZ-KNUDSEN-LANGMUIR'S equation, and values of evaporation rate constant of iron, KOFe, is obtained. Evaporation of manganese is controlled by the rate of diffusion in the bath, and the asymptote by R. G. WARD is introduced to calculate the values of KMn under an assumption of KOFe=KMn at the boiling point of iron.
    The difference on the evaporation phenomena of iron researched as the "Counter-Flux-Transfer" theory and those at the hot spot of oxygen jet of BOF process are made clear. Effects of oxygen dissolved in iron on surface activation and relation between fume formation and decarburization reaction are discussed.
  • Study on Heat Buckling and Shape Problems during Roller Quenching in the Continuous Annealing Line

    pp. 839-846

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    In the operation of continuous annealing lines for thin strips, one of the main problems is to ensure a good flatness especially during roller quenching.
    This paper deals with the heat buckling of strip during roller quenching and the pinch defect, namely, folding up of the buckled portion on the roller.
    The theoretical analysis on those phenomena is carried out. It allows clarification of those mechanisms, factors and countermeasures.
    The pinch index is presented, quantitatively showing the influence of various factors on pinch defects. This index gives the prediction for shape defects in actual operation, and is useful for its prevention and the design of the roller quenching system in the continuous annealing line.
  • Effect of Al and N on the Toughness of Heavy Section Steel Plates

    pp. 847-854

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    The effect of Al and N on the notch toughness and tensile strength of heavy section pressure vessel steel plates is investigated. Notch toughness of steel A533B (Mn-Mo-Ni), which has mixed microstructure of ferrite and bainite, is drastically changed by the ratio of sol.N/sol.Al. With metallurgical observations, it is revealed that AlN morphology is influenced by the ratio of sol.N/sol.Al through the level of solute Al (CAl). At the heat treatment of heavy section steel plate, AlN shows OSTWALD ripening and its speed depends upon CAl. When Al is added (Al≥0.010%) in steel and sol.N/sol.Al≤0.5, CAl remains low. This prevents AlN ripening, and brings fine austenite grain size and high toughness. On the other hand, when sol.N/sol.Al<0.5, CAl becomes high and this gives poor toughness through coarse AlN precipitates and coarse austenite grain. Therefore, controll of sol.N/sol.Al over 0.5 is favorable to keep high toughness in A533B steel. In steel A387-22 (Cr-Mo) which has full bainitic microstructure, too fine austenite grain brings about poor hardenability, and polygonal ferrite, which brings about both poor strength and toughness, appears in mi crostructure. Then sol.N/sol.Al<0.5 is better to give high hardenability in steel A387-22.
  • Antioxidation Mechanism of Si-SiC Oxidation Inhibitor for Grain-oriented Silicon Steel

    pp. 855-862

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    Antioxidation mechanism of a newly developed oxidation inhibitor of refractory powder mixture composed of SiO2, Si, SiC, synthetic mica, colloidal silica, surface active agent, and coking bond has been investigated.
    During heating, Al2O3 is formed as a result of the decomposition by Si (metallic silicon) of mullite (3Al2O3·2SiO2) contained in refractory powder. Furthermore, the fine SiC powder is oxidized and changes gradually to a protective cristobalite-SiO2 (C-SiO2) layer which acts as an excellent diffusion barrier to oxygen from atmosphere. The protective C-SiO2 is not formed from the C-SiO2 which is added in the oxidation inhibitor but is formed through the oxidation process of the SiC.
    On the other hand, Al2O3 which is formed by the decomposition of mullite becomes Al2O3·SiO2 in combination with SiO2. On the steel surface, however, Al2O3 becomes highly protective FeO·Al2O3or 3FeO·Al2O3·3SiO2 layer and, at the same time, it prevents the formation of a low melting point material such as fayalite (2FeO·SiO2).
    It has been clarified that this oxidation inhibitor exhibits the excellent antioxidability due to superposed effect of above-mentioned reactions.
  • High Temperature Oxidation of Fe-Cr Alloys in Ar-10% H2O Atmosphere

    pp. 863-870

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    In order to elucidate the phenomena and mechanisms of oxidation of Fe-(9, 17%)Cr alloys in Ar-10%H2O atmosphere at 1 000-1 400 K, the thickness and the morphology of scales formed were investigated.
    The scales usually consisted of the outer scale and the subscale. The oxide phases of these scales were identified as FeO and the mixtures of FeO and FeCr2O4, respectively. With the increase in Cr content in the alloys the rate of the total oxidation decreased, but the rate of the subscale formation increased.
    At all the temperatures parabolic kinetics was observed in the subscale formation, and its apparent activation energies were estimated to be 141 kJ/mol for Fe-9%Cr alloy at temperature above 1 100 K and 214 kJ/mol for Fe-17%Cr alloy at temperature above 1 000 K, respectively. The rate determining diffusion elements were considered to be Fe in FeO for the former alloy and Fe and Cr in α phase for the latter alloy.
    As for the subscale configurations, in Fe-17%Cr alloy only a continuous subscale formation was observed, whereas in Fe-9%Cr alloy the characteristic subscale was observed to form periodically. The periodic growth of FeO and FeCr2O4 can be explained by a Liesegang phenomenon, because the kinetics of the subscale formation is parabolic and the subscale formed periodically obeys JABLCZYNSKI'S relationship.
  • High Temperature Oxidation of Fe-Ni Alloys in Ar-H2O Atmospheres

    pp. 871-878

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    The oxidation of Fe-(9, 36%)Ni alloys at 1 000-1 400 K has been studied in Ar-(1, 5, 10%)H2O atmosphere using metallographic and electron probe microanalysis techniques.
    The scales consisted of the outer scale and the subscale which had a typical substructure of intergranular oxide zone and a metal/oxide mixed zone. The oxide phase in each scale was identified as FeO. With the increase in Ni content in the alloys the total oxidation rates decreased, but the growth rates of subscale increased.
    The oxidation rates and morphologies of the scales did not depend on the partial pressure of H2O in the range between 1 and 10 percent in Ar gas.
    At all the temperatures the subscales grew according to a parabolic rate law, and the apparent activation energies for the processes were estimated to be 129 kJ/mol for Fe-9%Ni alloy at temperature above 1 100K and 111 kJ/mol for Fe-36%Ni alloy at temperature above 1 000 K, respectively. The rate determining diffusion element in these alloys was considered to be Fe in FeO.
  • Corrosion Behavior of Austenitic Heat Resisting Steels in High Temperature and High Pressure Steam Environment

    pp. 879-886

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    Using a steam corrosion testing apparatus operating under almost the same steam conditions as those in actual boilers, the influences of temperature and pressure (especially above critical pressure) on steam corrosion were investigated for austenitic heat-resisting steels such as SUS 347HTB, 17-14CuMo, and the newly-developed 20Cr-25Ni and 22Cr-35Ni steels for advanced fossil steam plants.
    Corrosion loss in weight increases with increase in steam pressure and temperature. Increasing Cr and Ni content improve the corrosion resistance. Concentration of Cr in inner scale, (Cr, Fe)2O3, increases with Cr content of steel. This causes the higher resistance to steam corrosion. A Ni-enriched layer formed at the Cr2O3/metal interface contributes to the improvement of steam corrosion resistance. The Ni concentration in the layer becomes higher as steels contain higher Ni. Structural investigation of the scale cross sections shows that considerably large amounts of voids and cavities are produced in the scale of SUS 347HTB and 17-14CuMo steels corroded in steam at high temperature and pressure.
  • Degradation of SUS 304 by High Temperature Exposure and Recovering Heat-treatment Effect

    pp. 887-894

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    The degradation of mechanical properties of SUS 304 during high temperature exposure were investigated by comparing as solution treated specimen with the specimen serviced for 120 000 h in an ethylene plant. Additionally, a restoration of mechanical properties was examined by applying the re-solution treatment to the specimen serviced for the prolonged time, and the microstructural change which affected the degradation was discussed. There was little difference in short time tensile properties among the above three different specimens, except for rupture ductility. More than half decreases in a creep resistance, a creep rupture strength and an impact property were detected in serviced specimen. All these properties, however, could substantially be restored by the application of re-solution treatment to the serviced specimen. The degradation of these mechanical properties during high temperature service were mainly caused by the intergranular precipitation of a sigma phase, and the decrease in density of carbide precipitates, accompanied with the intergranular precipitation of a sigma phase.
  • Effects of Testing Conditions on Serrated Deformation of Austenitic Steels at Very Low Temperatures

    pp. 895-902

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    Tensile deformation behavior of metals at very low temperatures has been investigated using mainly Fe-42%Ni alloy in order to make sure the applicability of the computer simulation method presented by the authors and to clarify effects of testing conditions on serration. The amount of elongation accompanied with each load drop in serration increased with the increase in deformation rate and with the decrease in gauge length. Hourglass type specimen showed serration similar to that observed in specimens with smoothly reduced section. Serration was smaller in liquid He(II) than in liquid He(I). All these characteristics of serration observed experimentally were produced by computer calculation. Using computer simulation, it was clarified that the increase in thermal conductivity and diffusivity decreased the amount of elongation accompanied with load drops in serration. Simulation also showed that work hardening played an important role in determining serrated deformation behavior at very low temperatures. However serration was observed even when work hardening was not considered in calculation and specimen was deformed only at the central region of the specimen. Deformation behavior observed experimentally was discussed using such results obtained by simulation.
  • Validity of Dynamic Elastic-Plastic Fracture Toughness Values Measured by Instrumented Precracked Charpy Test

    pp. 903-909

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    In this paper, the validity of dynamic elastic-plastic fracture toughness Jd value by the developed evaluation system is studied on the steel for reactor pressure vessel. The effectiveness of the new system for the evaluation of the dynamic fracture toughness is also examined and proved on other kinds of materials such as aluminum alloy, Ti alloy, ductile cast iron and various steels.
    Moreover, the simple formura for the calculation of the specimen compliance (Cs) under dynamic loading condition, which is necessary for the correction of the crack initiation energy whenJd is evaluated, is presented.
    Elastic-plastic fracture toughness is generally affected by the specimen size. The valid condition for the specimen size under static loading condition is defined in ASTM E813-81. The valid condition for the specimen size determined under dynamic loading condition based on the same procedure appears severer than that of ASTM E813-81. However, it is clarified that the valid dynamic elastic-plastic fracture toughness (JId) is possible to obtain from small specimen such as the standard Charpy size one with the side grooves.
  • The Optimum Condition to Obtain the Maximum Hardenability Effect of Boron

    pp. 910-917

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    The effect of N, Ti and B on the hardenability of low and middle carbon steels has been studied, in order to make clear the optimum condition for obtaining the maximum hardenability of boron(B)-steels. The main results are as follows:
    (1) The hardenability of B-containing steel is expressed by the following equation:
    In the case of [B] ≤5 ppm, logVC-90=logVC-90°-0.14 [B], and when [B] ≥5ppm, VC-90=0.2VC-90°.where VC-90 is the hardenability defined as critical cooling rate (°C/s) at which 90% of martensite is formed during cooling in B-containing steel, and VC-90°is the hardenability as shown above in the base steel (B-free steel), and [B] is soluble B content (ppm). This means that the effect of B becomes maximum and constant when soluble B content exceeds 5 ppm.
    (2) The B-precipitate observed by α-autoradiography can be considered as BN because that the resolve temperature of the B-precipitate coincidents well with that of BN. Therefore, the amount of BN and/or resolved B can be calculated by widely used solubility product of B-N.
    (3) Boron-factor (fB), defined by GROSSMANN, is a function of the hardenability of the base steel (B-freesteel) as well as [B] as shown below.
    [B] ≤5ppm, fB=1-F/b·DI°
    where, F is a function of [B], and b is constant, DI° is the hardenability expressed by ideal critical diameter of the base steel.
  • Empirical Verification of GROSSMANN'S Equation

    pp. 918-924

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    According to GROSSMANN'S equation, the effect of alloying element on the hardenability of a steel is expressed in terms of the multiplying factor. Its reliability, however, becomes doubtful since it was confirmed that B-factor is not a function of only B-content. Therefore, in order to confirm whether GROSSMANN'S equation is reliable or not, the relation between a multiplying factor of different alloy element and its content has been investigated. The results obtained are as follow:
    1) The multiplying factor fX is a function of DS as well as content of alloying element X. DS is the hardenability of the steel before addition of alloying element. X. With increasing DS, fX becomes smaller.
    2) Boron factor, fB, is a function of DI° and shown as follows,
    fB=1+1.6/DI°, where DI° is the hardenability expressed by ideal critical diameter of B-free steel.
    3) Accordingly, GROSSMANN'S equation is not always realized. When DS is smaller than 2 inch and the hardenability of the steel after alloying element added is less than 33.5 inch, GROSSMANN'S equation is available. 4) There is more intimite relation between the critical cooling velocity and alloy content, X than between DI and X. DI is ideal critical diameter of a steel.
  • 武田信玄の愛読書/統計/夢物語

    pp. 935-935,939

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