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

Tetsu-to-Hagané Vol. 58 (1972), No. 6

  • 進歩と調和

    pp. 673-674

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  • Theoretical Analysis of Oxidation Reaction Taking Place in Molten Steel during Refining Process

    pp. 675-684

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    Oxidation reactions taking place in molten steel in the various refining processes have correlation with each other through oxygen in a steel bath as a medium of the reactions and the transitional variations of each concentration of the reaction components in molten steel may be determined on the basis of the balances of the following two kinds of driving forces. Namely, one force has a essential tendency allowing the system to approach to the equilibrium, and another force caused by oxygensupplied into a bath acts in the opposite direction and has a tendency to keep the system away from the equilibrium.
    On the basis of the function of the driving forces mentioned above, a simplified model is proposed in this paper, and the important-dimensionless factors, A and B, determining the effects of the feeding rate of available oxygen, the degree of mixing of molten steel and the temperature of molten steel on the transitional variations of process variables are involved in the model.
    By the use of this model, the experimental data of oxidation reactions obtained by the other investigators were quantitatively analysed, and the differences in the proceeding sequence of the oxidation of silicon and the decarburization which were widely known from the comparison between the experimental data obtained in LD converter and those in the crucible were clarified quantitatively in this work.
  • On the Coagulation of Inclusions in Deoxidation with Silicon-Manganese

    pp. 685-693

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    It is well known that coagulation of inclusions plays an important role in removal of them in deoxidation of steel with silicon-manganese. The influence of chemical composition of inclusions on the coagulation in static iron melt was investigated.
    The results obtained are as follows;
    1) The compositions of the primary inclusions in the initial period of deoxidation deviated from those in equilibrium with iron melt.
    2) The inclusions tended to be enriched in MnO when manganese had been added prior to siliconmanganese.
    3) The floating velocity of inclusions was expressed by Stokes' one or 3/2 of it.
    4) The coagulation of inclusions on the way of floating in iron melt took place actively at a ratio [Mn]/[Si]=4 in which liquid inclusions only precipitated in the initial period.
    5) Solid silica in inclusions seems to suppress the coalescence of the inclusion particles touched each other and to reduce the coagulation.
  • Development of a New Ladle Refining Method

    pp. 694-704

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    A new style ladle refining method has been developed. This method is characterized by stirring and heating the molten metal in the ladle to refine it.
    This stirring method is based on Fleming's left-hand rule, that is to say, the force is generated by direct electric current through the molten metal in direct magnetic field. Direct magnetic field and current are designed so that molten metal circulated up and down to be suitable to stirring in the ladle. The molten metal is heated by arc.
    First, experiment was made using small scale equipment to refine 200kg steel. By stirring, chemical compositions after alloy addition and metal temperature were found completely uniformed.
    Scale-up method was studied theoreticaly, and 2.7 ton equipment was designed based on theoretical scale-up method and standard dimensions obtained on experiment of 200 kg equipment.
    By this ladle refining process, better quality steel was obtained compared with that of normal arc furnace steel making process.
  • On the Relation between Flatness of Rolled Strip and Profile of Roll Crown

    pp. 705-725

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    The aim of present work is to investigate basically and experimentally the rolling condition under which the strip of flat shape can be obtained with a multi-high rolling mill having the working roll of smalles diameter.
    By using the rolls with various profile, the roll indentations were impressed on the strip surface by means of static screw-down without roll revolution under the various forces. Then, the transverse distribution of roll indentation width, namely, the variation on width of roll indentation in the direction of strip width was measured, and a consideration was made on the correlation between these and the flatness of strip rolled under the same condition as static screwdown. It was shown that the transverse distribution of roll indentation width was equivalent qualitatively to the flatness of rolled strip.
    The more appropriate profile of working roll crown for rolling the strip of flat shape with present mill was accorded closely with the cornered or rounded curvature rather than parabolic one which may be suitable for two-high mill.
    The relation between flatness of strip and the shape of 1st-intermediate backing roll, and the trend of working roll deflection under static screw-down were also shown.
  • Study of the Precipitation of x-Carbide in the Tempering Process of Some High Carbon Steels

    pp. 726-740

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    In order to make clear the precipitation behaviour of iron-carbides, especially the existence or non existence of X-carbide, in the tempering process of steels, observations were made of some quenched and tempered high carbon steels containing 0.86-1.34 wt pct carbon by transmission electron microscopy. Thermomagnetic and thermal dilatational measurements were also made for comparison's sake. The main results obtained are summarized as follows:
    (1) In the high carbon steels tempered under appropriate conditions, X-carbide can be observed by transmission electron microscope.
    (2) Habit plane of X-carbide is determined to be {112}α suggesting that the carbide may precipitate preferentially on martensite twin boundary.
    (3) In electron micrographs, morphology and growth direction of X-carbide are different from those of ε-carbide, but are very similar to those of θ-carbide which precipitates on {112}α. From these observations, separate nucleation and in situ transformation are supposed for ε→x and Xθ transition, respectively.θ-carbide precipitating on {110}α a is also found, and is suggested to take place by separate nucleation directly from ε-carbide.
    (4) Using three main crystal indices of planes and direction in X-carbide, i. e., (100)x, (010)x, and [001]x, the orientation relationship of the carbide with ferrite matrix is approximately expressed as (100)z≈//(121)α, (010)x≈//(101)α, and [001]x≈//[111]α.
    (5) By thermomagnetic and thermal dilatational measurements, the precipitation of X-carbide is also detected on the high carbon steels tempered under the most favourable condition to obtain X-carbide.
  • Rolling Textures and Anisotropy in Mechanical and Magnetic Properties in Unidirectionally Solidified and Cold-Rolled 18-8 Stainless Steel

    pp. 741-750

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    18-8 stainless steel ingots solidified unidirectionally were cold-rolled in the longitudinal, transverse and perpendicular directions of columnar crystals.
    During cold-rolling to 95% reduction in thickness, all the specimens transform from γ phase to a phase. This strain-induced transformation proceeds most slowly in the specimen cold-rolled in the direction parallel to the growth direction of columnar crystals.
    The cold-rolling textures of α phase consist mainly of {211}‹011› and {100}‹011› orientations.{211}‹011› orientation is the major component of the specimen rolled in the direction parallel to the growth direction of columnar crystals, whereas it is {100}‹011› orientation for the other specimens.
    The maximum value of Young's modulus is obtained by cold-rolling and subsequenttempering at 550°C. Lowering of saturation magnetization, rise of coercive force, and increase in the magnetic anisotropy by tempering at around 600°C are supposed to be correlated with the shape anisotropy of ferromagnetic α phase in non-magnetic γ phase, formed by reverse transformation.
  • Effect of Cooling Rate after Solution Heating on the Mechanical Properties and Age Hardening Properties of 21-12N Steel

    pp. 751-763

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    The effects of various cooling procedures from solution temperature, i. e. water quenching, air cooling and furnace cooling, etc., on the mechanical properties of 21-12N steel before and after ageing were investigated.
    It was found that the tensile strength and 0.2% proof stress of specimens before aging were not affected by the cooling rate, whereas the maximum hardness was obtained after water quenching. The ductility and the type of fractures after solution treatment were also affected by the shape of grain boundaries as well as by the amount of grain boundary precipitates formed during cooling at various rates.
    It was also found that the age-hardening characteristics changed appreciably with cooling procedure. According to the transmission electron microscopy the remarkable hardening during high-temperature aging after water-quenching was attributed to the fact that the high dislocation density resulted in large amount of fine precipitates of M23C6 which are formed mostly on dislocations.
  • The Effect of the Transformation Structure on the Mechanical Properties of Molybdenum Steels

    pp. 764-772

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    In molybdenum steels a structure called divorced pearlite, consisting of blocky carbide and ferrite, is induced with higher Mo/C ratios and elevated transformation temperatures, while a lamellar pearlite structure develops with lower Mo/C ratios and/or lower transformation temperatures.
    Experiments have been carried out to clarify the effect of pearlite morphology on the mechanical properties using steels with different Mo/C ratios (0.02, 0.47 and 1.17) transformed at various temperatures ranging from 675°C to 500°C.
    It has been shown that in steels having the lamellar pearlite structures, the Charpy transition temperature is lowered and the shelf energy is increased with decrease in interlamellar spacing. The finer interlamellar spacing gives rise to the increased tensile and yield strength.
    Divorced pearlite structures, however, are found to deteriorate the impact and tensile properties.
    M23C6 carbide, besides M3C, is observed to form at higher transformation temperatures in steel with the highest Mo/C ratio, but carbide pcr se has no significant effect on the mechanical properties.
  • Corrosion Products of Pure Metals in V205 Melt

    pp. 773-786

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    Corrosion products of iron, cobalt, nickel, zirconium, chromium, and titanium in V205 melt were examined by metallography, electron probe microanalysis, and X-ray diffraction. The main results obtained are as follows:
    (1) Iron. FeVO4 and FeV206 in addition to wustite, magnetite, and hematite, were found in the corrosion products at 850°C. FeVO4 and FeV206 were detected in the places which were melt at the test temperature. Magnetite layer formed at 850°C contained vanadium and its composition was considered to be (Fe1-xVx) 3O4, while magnetite layer at 750°C did not contain vanadium.
    (2) Cobalt. A porous and thick scale layer formed at 850°C mainly consisted of Co3V2O8, and a considerably large amount of cobalt was observed in V205 melt.
    (3) Nickel. A dense scale layer formed at 900°C mainly consisted of Ni3V2O8, and only a small amount of nickel was detected in V2O5 melt. Low oxidation rate of nickel is considered to be due to the formation of the dense Ni3V2O8 layer.
    (4) Zirconium. ZrO2 was formed at 850°C, and the scale was so porous that V2O5 melt penetrated into the innner part. The formation of ZrV2O7 besides ZrO2 was observed at 700°C.
    (5) Chromium. Solid CrVO4 was observed in the scale in addition to Cr2O3 at 850°C. The former is considered to contribute to the good corrosion resistance of chromium.
    (6) Titanium. The formation of TiO2 (rutile) was observed.
  • Structural Problems of the Deoxidation Products in Steel

    pp. 787-810

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  • 抄録

    pp. 811-817

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