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

Tetsu-to-Hagané Vol. 57 (1971), No. 6

  • 随想

    pp. 883-884

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  • Improvement of Reducibility by Pre-reduction in Low Temperature

    pp. 885-890

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    Self-fluxing sinter, basic pellet and acidic pellet were pre-reduced at low temperatures (500, 600 or 700°C) for several minutes, then heated quickly and reduced again at a high temperature (900°C). The gas utilization coefficient at the same reduction degree was increased by the pre-reduction. This effect was the largest in the case that the pre-reduction temperature was 600°C and the pre-reduction degree was 11%.
    Using the parallel model with 3 interface reductions, reaction rate constants for wustite, magnetite and hematite reduction were calculated from these experimental data by electronic computer. The reaction rate constant on the reduction from magnetite to wustite, Kma and that from hematite to magnetite, Khe were increased by pre-reduction at low temperature, but that from wustite to iron, Kwu, was remained unchanged. In the case of sinter, Kma and Khe were increased about 3 times on the pre-reduction at 600°C, and about 2 times at 500°C and 700°C.
    This effect may be considered with the calculation of countercurrent reduction of descending ore bed.
  • Equilibrium between FeO-MnO-Al2O3 Slags and Molten Iron

    pp. 891-902

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    The experimental work on the equilibrium between molten iron and FeO-MnO-Al2O3 slags at 1560°C has been carried out to determine the activities of the constituent oxides.
    In the range of liquid slag composition, the activity of iron oxide shows positive deviation from ideality, which is increased with increasing alumina contents and attains to maximum at about 50mol% FeO composition regardless of alumina contents.
    On the other hand, the activity of manganous oxide shows a progressive slight increase in negative deviation from the ideal solution law as the slag composition increases in alumina or manganous oxide contents.
    Isoactivity diagram of the constituent oxides for the FeO-MnO-Al2O3 slags and isoconcentration diagram for the molten iron in equilibrium with those slags are established by the calculation based on DARKEN'S quadratic formalism and experimental data.
    A statistical mechanical treatment is applied to derive the thermodynamic behavior of the FeOMnO-Al2O3 slags and the results are compared with those obtained by the same treatment for FeOMnO-SiO2 system.
  • On the Behavior of Oxide Inclusions during the Steelmaking Process of Top-Teeming High Carbon Chromium Steel

    pp. 903-914

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    In order to investigate the source of oxide inclusions, variation in the composition and the microscopic structure of oxide inclusions in steelmaking process of top-teeming high carbon chromium steel were investigated.
    In addition, oxide inclusions in ferrosilicon and effect of the use of low aluminium ferrosilicon on oxide inclusions in steel were also investigated.
    The results were summarized as follows.
    (1) It was found that spinel (MgO·Al2O3), a main constituent mineral of oxide inclusions, was produced by mutual reaction of deoxidation product formed by Al or aluminate inclusions in ferrosilicon with slag particles containing MgO3, when ferrosilicon was added and mixed at the end of refining period.
    (2) Increasing rate of Al203 content in molten steel was lowered by the use of low aluminium ferrosilicon, as compared with the use of commercial grade ferrosilicon. It resulted in decrease of Al2O3 content in the molten steel before tapping and in the ingot bottom. However, microscopic structure and mineral composition of oxide inclusions in steel were same as in the case of the use of commercial grade ferrosilicon.
    (3) It was noted that macroscopic inclusions were greatly affected by Al content in ferrosilicon.
    x

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    1. Thermodynamics of Reaction between Trace Amount of Al and Inclusion in Mn-Si Killed Steel ISIJ International Vol.36(1996), No.Suppl
  • On the Accumulation Mechanism and the Reducing Process of Large Non-metallic Inclusions in the Bottom Equiaxed Zone of Ingots

    pp. 915-941

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    A solidification process of 6-t slab ingots poured at high or low temperature is investigated by means of radio-isotope, temperature measurement, and direct sampling of mushy zone. The accumulation mechanism of large non-metallic inclusions in the bottom equiaxed zone of a ingot is described. The accumulation of large non-metallic inclusions in the bottom part of ingot relates closely with the phenomena occurring in the retained molten steel in the ingot, especially with a rapid development of mushy zone. In the case of ingot poured at low temperature, the growth of mushy zone is rapid owing to the crystallization of crystallites and their falling down to the bottom of ingot, which are remarkable at an early stage of solidification. This rapid growth of mushy zone prevents the floating of suspended inclusions and traps them to accumulate at the bottom part of ingot. The floating of inclusions trapped at the mushy zone of ingot would be difficult because of high apparent viscosity of the mushy zone. And they would grow to macroscopic size during the mushy state and the growth proceeds until completion of solidification. In the case of ingots poured at high temperature, on the other hand, a few crystallites crystallize and fall down at an early stage so that the mushy zone grows slowly. Inclusions would not be trapped but float out because of low viscosity of molten steel. This makes sound ingots. Since the formation of macroscopic inclusions depends on the rate of mushy zone development, macroscopic inclusions are few at columnar zone that is formed without precedence of the mushy stage even at the bottom of ingot, and they are rich at bottom equiaxed zone that is formed with being preceded by the mushy stage.
  • Effect of Nonmetallic Inclusions on Impact Property of Steels

    pp. 942-953

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    In order to study the relationship between FeO type inclusions and impact property of steels, 30-kg U-notched charpy impact test of specimens with different oxygen content was carried out. The fracture surfaces obtained by this test were observed with an electron microscope by two-steps carbon replica technique or directly with a scanning electron microscope and the profiles of these fracture surfaces were observed with an optical microscope. A quantitative estimation was made on the degree of effect of FeO type inclusions on impact property of steels, on the basis of the relationship between absorbed energy in impact test and the number of inclusious associated with the fracture surface.
    Some of the results obtained are as follows:
    1) Impact property becomes worse with an increase in inclusion content. But the effect of inclusion content on absorbed energy in brittle fracture range can not be recognized.
    2) FeO type inclusions seem, in some cases, to act as barriers to the propagation of cleavage crack.
    3) The degree of effect of FeO type inlusions on impact fracture increases with an increace in grain size of specimen.
  • A Study on Temperature and Strain Rate Dependences of Yield Stress at Low Temperatures in Pure Iron and Fe-Cr Alloys

    pp. 954-964

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    Temperature and strain rate dependences of yield stress in purified pure iron and Fe-Cr alloys, were studied mainly by compression tests in the ranges of -196-300°C of temperature and 10-5-10-2sec-1 of strain rate.
    Relations between temperature (T), strain rate (ε) and frictional stress (σt), were established in the following manner:
    ε=Cσnt exp(-E/RT)
    This is applicable when at is in the range of 5-28kg/mm2. Activation energy E is hardly dependent on temperature, stress and chromium concentration, being about 15 kcal/mol. Strain rate exponent n, however, increases with increasing chromium content. It may be said that solid solutioning of chromium affects mainly n and C in the above equation, and further, that stress is chiefly attributable to entropy term rather than to enthalpy.
    Softening effect by solid solutioning is presumed to be mainly due to the increase of the strain rate exponent with increasing chromium concentration, in other words, to the increase of activation volume.
  • Manufacturing Method of High Purity Iron by Zone Refining and the Measurement of the Purity

    pp. 965-977

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    High purity iron was manufactured by zone refining under wet and dry hydrogen atmospheres.
    The original materials were reelectrolytic iron, a common specimen of the Iron and Steel Institute ofJapan (specimen number 958, 960), Johnson Matthey iron, and Puron iron. The residual resistivityratio (RRR) was used to show the purification degree and the longitudinal magneto-resistance effect wasinvestigated at 4.2°K.
    As one of the physical properties, the thermoelectromotive force (EMF) was studied and the relation between EMF and RRR was investigated.
    The results were summarized as follows:
    (1) The slower the travelling rate of zone refining was, the greater the purityofspecimen became.
    (2) The more the number of zone pass was, the greater the zone refining effect became.
    (3) It was very difficult to eliminate Cu, Co and Ni from the reelectrolytic iron.
    (4) The value of RRR min, was obtained in the magnetic field of 800-900 Oe.
    (5) The value of RRR min was independent on the electric current in the range from 50 to 450m A.
    (6) The non-deoxidated common specimen of the Iron and Steel Institute of Japanwas purifiedb y zone refining more than the deoxidated one was.
    (7) It was effective to anneal the sample at 800° in wet hydrogen atmosphere after zoner efining.
    (8) Specimen covered with calcium fluoride was refined by zone melting in wet hydrogen and RRR of its specimen was fairly good.
    (9) The thermoelectromotive force could be used as one of the methods of the purity measurements when RRRmin was less than 200.
  • Precipitation of A1N in High Purity Fe-Al-N Alloy

    pp. 978-985

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    High purity Fe-Al-N alloys were prepared using zone-refined iron (>99.99%), and precipitation process of AlN from solid solution was studied. Two kinds of specimens were prepared, one was assolution-treated and the other was as cold-worked after solution treatment of 1 250°C×1hr. Afterthese specimens were annealed isochronally, the electrical resistivities were measured in liquid nitrogen.
    The result shows that large decreases of the resistivity are found in the temerature range from 400°Cto 700°C, and the temperature of the decrease shifts to a lower side as the specimens are cold-worked.
    The specimens as solution-treated were isothermally annealed at the temperature range from 600°C to 700°C, where the large decrease of the resistivity was noted in the isochronal annealing, and theirelectrical resistivity and internal friction were measured. The results obtained are as follows;
    (1) Activation energy of this process is found 53 kcal/mol.
    (2) In this process exists some incubation period for nucleation.
    (3) The apparent order of this chemical reaction γ derived from -dn/dt=nγK is found to beabout unity.
    (4) Normalized resistivity change coincides with normalized change of N Snoek peak.From these results, it may be deduced that the large decrease of the resistivity can be attributed tothe precipitation of AlN, that the rate of the process is controlled by the diffusion of Al atoms in airon, and that the process can be expressed by an equation of chemical reaction, Al+NAIN, with unequal initial concentrations of reactants. The last deduction was confirmed by experiments of alower Al content alloy (Fe-0.02 Al-N).
  • An Experimental Analysis on the Temperature Measurement of Molten Iron and Iron Alloys by Two-Color Pyrometer

    pp. 986-995

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    It is known that the temperature read by two-color pyrometer, generally, do notstrictly indicate thetrue one. Therefore, it is necessary for measuring the temperature precisely by two-color pyrometer toprovide some adequate procedures. In order to obtain some informations for this compensation, themelting points of several compositions of both Fe-Ni and Fe-Cu alloys were measured by use of twocolorpyrometer, and the characteristics, especially the spectral emissivity ratio for two different wavelengthsε1/ε2 of two-color pyrometer were discussed through this experimental result.
    The main results obtained were summarized as follows:
    1) In liquid Fe-Ni alloy the value of ε1/ε2 decreased with increasing nickel concentration over allrange of composition, while in liquid Fe-Cu alloy the ratio also decreased gradually up to about 60%Cu but abruptly above this composition with increasing copper concentration. These data seem to beuseful as the practical coefficients converting from two-color temperature to true one for the bothalloy systems.
    2) In order to accurately measure the temperature of any kind of metals and alloys by two-colorpyrometer, the relation between two-color and true temperature is desired to be derived by WIEN'Sequation through the measurement of their melting points, and moreover, the exact compensation forobtaining true temperature should be made using the values ofε1/ε2. obtained for each metal andalloy.
  • Management of Calibration Curves in the Absorptiometric Analysis

    pp. 996-1005

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    The principle of the absorptiometric analysis depends on the fact that the optical characteristics ofsample solution obeys the Lambert-Beer's law.
    The gradient of calibration curve, according to the law is constant under the same analyticalcondition.
    In the ordinary analysis, the average gradient of calibration curve, which was obtained with theempirically and theoretically reliable measures, was defined as the basic gradient, and the straight linedrawn through the origin with the basic gradient was named as the basic calibration curve here.
    The average blank value of each day, gained by the analysis of standard samples, was subtractedfrom absorbances of test samples and then the contents were read on the basic calibration curve.
    By applying this method to the analyses of Si, P, Ni, Mo, W, Ti, Co, and Cu, the daily deviationof gradient was eliminated and the better analytical precision was obtained.
    With a statistical treatment of data on standard samples it was easily capable of checking out theabnormal point on the daily process of analysis and ascertaining the stability of calibration curveduring a long period.
  • On Aluminum Oxy-nitride in Aluminum Treated Steel

    pp. 1006-1008

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    Chemical analysis and X-ray diffraction were carried out for residues which were isolated byhydrochloric acid (1+1) from steel specimens killed with aluminum. The results are as follows;
    All of the residues isolated from the present specimens are shown to be mixtures of α-aluminaand aluminum oxy-nitride which is in tetragonal structure of δ-alumina type from the analysis oftheir X-ray diffraction patterns. Aluminum oxy-nitride, like alumina, is so stable to mineral acidthat the existence of this kind of oxy-nitride causes lower analytical results of nitrogen by rapid Kjeldahl, s method. In some other studies on aluminum nitride in steel, it has been reported that thenitride seems occasionally to be undissoluble in mineral acids. The authors concluded from this study, however, that the compound containing nitrogen in the residue isolated by mineral acids is aluminumoxy-nitride and not nitride.
  • Crystal Structures of Transition Metal Carbides

    pp. 1009-1053

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  • General Outlook of European Iron and Steel Industry

    pp. 1054-1065

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  • On Application of Nuclear Energy to Iron Making Process

    pp. 1066-1082

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  • 抄録

    pp. 1083-1090

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