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

Tetsu-to-Hagané Vol. 64 (1978), No. 14

  • 鉄とスラグ

    pp. 2099-2100

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    Readers Who Read This Article Also Read

    1. Heat Transfer Phenomena in Immersion Cooling of Heated Steel Plate and Influence of Water Stirring on Heat Transfer Tetsu-to-Hagané Vol.64(1978), No.1
    2. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    3. 第95回講演大会討論会講演概要 Tetsu-to-Hagané Vol.64(1978), No.2
  • Sulfurization of Prereduced Sponge Iron Pellets by COS-CO Gas Mixtures

    pp. 2101-2108

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    The rate of reaction of carbonyl sulfide with metallic iron was studied by measuring the ratt of sulfurization of sponge iron pellets in COS-CO gas mixtures at temperatures from 800°C to 1000°C. The sponge iron pellets had been produced by hydrogen reduction of hematite pellets.
    The results obtained are as follows:
    1) The product shell layers were proved to be nonstoichiometric ferrous sulfide having the atomic ratio of S/Fe=1.06.
    2) Negligible amount of carbon was deposited on the pellets in the stream of 5% COS-CO gas mixture.
    3) The sulfurization reaction was analyzed on the basis of the unreacted-core model and it was found that the reaction was controlled by the following three steps; the gas-film mass transfer, the intraparticle gaseous diffusion, and the chemical reaction at the sulfide-iron interface.
    4) The chemical reaction rate constant kγ and the effective intraparticle diffusion coefficient De are expressed respectively by the following Arrhenius type equations:
    log kγ= 3.053-13400/2.3 RT
    log De= 4.746-30430/2.3 RT
    It is noteworthy that temperature coefficient of De is fairly greater than that of kγ, which results in the predominant contribution of chemical resistance to the over-all resistance even in higher temperatures.
  • On the Pre-Treatment of Pig Iron by the Continuous Dephosphorization Furnace

    pp. 2109-2118

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    Continuous pre-dephosphorization process with 300kg trough type furnace was examined; with the hot metal input rate: 33-38kg/min, oxygen blowing rate: 0.7Nm3/min, and flux rate: 4-5kg/min. The slag was co-current with the metal. As the result of one and two lance-operations, it became clear that the two lance-operation was more advantageous for slag-metal reactions as predicted from the characteristics of the resistance model. Moreover, from a theoretical analysis it was proved that the slag-metal reactions could proceed most effectively when the gas-liquid flow rate ratio { (oxygen blowing rate +CO gas generating rate) / hot metal rate} of each lance was kept equal.
    By utilizing the result of this investigation it would be possible to develop a continuous pre-treatment process of hot metal with higher dephosphorization ability by optimizing the physical conditions of the process and by the operation such as the adoption of countercurrent.
  • Dissolution and Transport Phenomena of Deoxidizing Elements into Quiescent Molten Iron

    pp. 2119-2128

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    This work was carried out to obtain the knowledge of dissolution and the transport phenomena of deoxidizing elements into quiescent liquid iron.
    Deoxidizers were added as block state or as liquid state on the surface of liquid iron melted in a tammann furnace. Changes of the temperature near the surface of the liquid iron were measured with thermocouples. After a predetermined holding time in the furnace, each heat was rapidly quenched into water. Concentration contours of deoxidizing elements were obtained on the surface by XMA point analyses. The results obtained are summarised as follows.
    (1) When deoxidizer was added as liquid state, the deoxidizing elements were transferred into liquid iron by diffusion. The diffusion co-efficient of aluminum in liquid iron was obtained as 1.12×10-4 cm2/sec.
    (2) When deoxidizer was added as block state, the temperature near the surface went down. Owing to this temperature-drop, convection in the liquid iron occurred and deoxidizing elements were transferred with convection. This convection in the case of solid aluminum with dense and tight oxide film was stronger than that of silicon without a tight oxide film.
    (3) When aluminum was transferred with convection, it produced high concentration regions. These regions floated up without reaction and diffusion. Owing to this phenomena, the yield of aluminum was scattered.
  • Formation Mechanism of Dendritic and Spherical Alumina Formed When Iron is Deoxidized by Aluminum

    pp. 2129-2138

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    This work was carried out to obtain the knowledge of the formation mechanisms of dendritic and spherical deoxidation-products. Aluminum was added as liquid state on the surface of the quiescent molten iron. After the specimen was quenched, its vertical section was analysed by XMA. The shapes of the deoxidation-products in the specimen were observed by SEM after deep etching.
    The results obtained are summarised as follows.
    (1) When the molten iron contains more surface active elements, the alumina/molten iron interfacial energy becomes lower. The lower this energy is, the smaller the critical super-saturation ratio for nucleation of alumina becomes. This critical super-saturation ratio is obtained as 5.55×108.
    (2) The dendritic deoxidation-products grown to aluminum-rich direction are α-alumina, and another grown to oxygen-rich is hercynite. These different shapes depend on the crystal structures. The smaller the super-saturation ratio is, the thinner the dendrites become along their principal axes, that is, they become acicular.
    (3) The spherical deoxidation-products are formed by remelting of α-alumina by increasing soluble aluminum, or from their liquid state as complex oxides with low melting points.
    (4) The clusters are grown by gathering of various deoxidation-products which have different floating velosities.
    x

    Readers Who Read This Article Also Read

    1. Heat Transfer Phenomena in Immersion Cooling of Heated Steel Plate and Influence of Water Stirring on Heat Transfer Tetsu-to-Hagané Vol.64(1978), No.1
    2. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    3. 第95回講演大会討論会講演概要 Tetsu-to-Hagané Vol.64(1978), No.2
  • Productions of Ultra Low Nitrogen Ferrochromium and of High Purity Stainless Steel with It

    pp. 2139-2147

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    The process of denitriding of low carbon ferrochromium and vacuum melting of high purity stainless steel with the denitrided ferrochromium were investigated.
    (1) A pile of granular ferrochromium can be denitrided uniformly with Mg-MgCl2 flux of more than 70-90 kg/t without mechanical stirring.
    (2) Under the condition that the terminal nitrogen content of ferrochromium is independent of its size, the influences of temperature, amount of flux, and initial nitrogen content can be explained thermodynamically as the equilibrium state is reached.
    (3) The optimum size of ferrochromium is 1-5 mm∅.
    (4) In VIF, if solid oxide is mixed in granular ferrochromium, the prevention of mitrogen absorption is possible owing to decarburization during melting. The denitrided granular ferrochromium is a suitable chromium source for the high purity, especially ultra low nitrogen, stainless steel.
  • On the Ductility of Steel near the Solidification Temperature

    pp. 2148-2157

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    As a part of the studies on the formation of the internal cracks in continuously cast slabs, the tensile properties of specimens sampled from various steel slabs were examined up to their solidification temperature and the effects of solute elements and solidification structure on the transition temperature from high to low ductility were investigated.
    The results obtained are as follows.
    (1) The mechanism of the abrupt transition to the low ductility is considered to be related to the melting of grain boundaries. The transition temperature, therefore, is lowered due to the increase of solute elements, and is also affected by the solidification structure of the specimen.
    (2) The lower the transition temperature becomes, the more easily the internal cracks occut in the continuously cast slab.
  • Effect of Nitrogen Content on Recrystallization Textures of Extra-Low-Carbon Steel Sheet

    pp. 2158-2166

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    Fully decarburized, fully denitrogenized and grain refined rimmed steel (extra-low-carbon and extralow-nitrogen steel) has been cold rolled to 75% in reduction, and subsequently nitrogen contents of the steel have been changed to various amounts up to 200 ppm. Nitriding has been made using a reaction between steel and atmosphere, NH3+H2, at 350°C, without forming any recrystallized grain. Finally these steels have been annealed at 650°C or 800°C for recrystallization.
    Recrystallization texture is markedly affected by the nitrogen content in steel at the stage of recrystallization annealing. {100} components of recrystallization texture decrease abruptly with increasing nitrogen content up to about 20 ppm, while {111} components decrease and {110} components increase with increasing nitrogen content up to about 100 ppm. Pole figures of the annealed steels show strong {111} {112} texture with minor {100} <011>texture for the extra-low-nitrogen steel, and strong {111} <011> texture with minor {110} <001>texture for the steels containing nitrogen of more than 20 ppm. Since {111} <112> and {100} <011> orientations are the major components of the cold rolling textures of the steel, it is suggested that in situ recrystallization occurs when nitrogen content is extremely low at recrystallization stage. The γ-value of annealed steels increases initially with nitrogen and decreases with increasing nitrogen. The maximum γ-Value of 2.0 is obtained when the steel contains nitrogen of about 10 ppm at recrystallization stage.
  • Effect of Nitrogen on Recrystallization Kinetics of ExtraLow-Carbon Steel Sheet

    pp. 2167-2176

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    Extra-low-carbon and extra-low-nitrogen steel has been cold rolled to 75% in reduction, and subsequently nitrogen contents of the steel have been adjusted to ≤2 ppm and 160 ppm by atmospheric reaction to the steel at 350°C. These two steels have been annealed at various temperatures at a constant heating rate, and their recrystallization behaviors have been investigated by X-ray diffraction analysis and electron microscopic observations.
    In the low nitrogen steel, recrystallization starts at low temperature, initially withont any change in texture, and at the later stage of recrystallization {111} components increase. While in the high nitrogen steel, recrystallization starts at higher temperature accompanied by slight decrease in {111} components and rapid increase in {110} components. According to the electron transmission studies of the steels in the early stage of recrystallization, rotation angles between recrystallized grain and adjacent recovered matrix are relatively small for the low nitrogen steel and large for the high nitrogen steel. These observations imply that in situ recrystallization which takes place with small-angle boundary migration or annihilation is preferred in the former steel and the growth of recrystallized grain by large-angle boundary migration from heavily curved regions in deformed matrix is predominant in the latter steel.
    These differences in recrystallization behavior by nitrogen content are believed to be caused by the strong interaction between dislocations and nitrogen atoms.
  • Relation between Precipitation Behavior of Mo, V and Nb and Yield Strength in Normalized and Tempered Steel

    pp. 2177-2186

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    The changes in the precipitation behavior of alloying elements and the yield strength due to normalizing and subsequent tempering of 0.15% C-1.4% Mn steels containing small amounts of Mo, V, Nb and Ni have been studied. The results are as follows: (1) The addition of any two or all of Mo, V and Nb to steel exhibits a synergistic effect on the increase in yield strength of normalized-tempered steel at room and moderate temperatures. (2) The amounts of Mo, V and Nb as precipitates increase by the coexistence of these elements in steel, compared to the simple sum of the amounts of precipitates in steels having any one element. (3) Fine precipitates of Mo2C and more frequently those of NbC and V4C3 were detected through electron microscopic analyses. Peculiarly shaped precipitate likely composed of two kinds of precipitates was also observed in steels containing Mo, V and Nb. (4) The increase in the cooling rate from normalizing temperature and the addition of Ni contribute to the increase in the amounts of Mo and V precipitated by tempering. This effect is attributed to the increase in the percentage of bainite structure after normalizing which has many dislocations and can prepare precipitation sites during tempering.
  • Crack Propagation Rates of SUS 321 Stainless Steel under High-Temperature, Low-Cycle Fatigue Conditions

    pp. 2187-2194

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    Crack propagation rates of SUS 321 stainless steel under high-temperature, low-cycle fatigue conditions were obtained from the observation of fracture surfaces. There were good linear relations between the crack propagation rate and the crack length in log-log plots, whether the fracture mode was transgranular or intergranular. The slopes in the log-log plots were varied from 1.2 to 1.5, but many of them were 1.3. The proportion of the cycles spent in Stage II to the fatigue life could be expressed as a function of the fatigue life. Its calculated proportion was coincident with the proportion of the number of striations on the fracture surface to the fatigue life. The crack propagation rate at 700°C could be expressed in terms of the plastic strain range, the strain rate and the crack length. This result was discussed in comparision with other studies.
  • Effects of Carbon, Nitrogen and Nickel Content on the Low Temperature Impact Value of High Manganese Austenitic Steel

    pp. 2195-2204

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    The purpose of this study is to examine the effects of C, N and Ni content on the Charpy impact value and tensile properties at subzero temperatures of high Mn austenitic alloys. The friction stress for Petch equation and load-time curve in Charpy impact test at -196°C have been determined. The effects of C and N on the stacking fault probability and fracture mode have also been examined.
    0.2% proof stress and tensile strength are found to increase linearly in proportion to C plus 1.5 times N. Tensile ductilities especially at cryogenic temperature decrease with increasing C and N content. Charpy impact values at the temperature down to -100°C do not change by the addition of C and N, however, those at -150°C and -196°C show decreasing tendency with increasing amount of C and N. Yield and maximum load obtained in the Charpy impact test at -196°C linearly increase with increasing value in C plus 3.3 times N. The fracture mode at -196°C changes from ductile to brittle when the value in C plus 3.3 times N exceeds 1.0.
    The improving effect of Ni on the impact value at -196°C can be estimated in terms of stacking fault energy. The embrittling effects of C and N are estimated in terms of stacking fault energy and according to Smallman equation predicting ductile/brittle fracture transition.
  • Improvement in Toughness of Large Heat-Input Weld Bond of 60kg/mm2 Grade High Tensile Strength Steel Plates due to Boron Addition and Low Silicon Content

    pp. 2205-2214

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    In order to obtain superior toughness of weld bond of large heat-input welded steel plate, the roles of boron addition and low silicon content have been investigated. BN particles precipitate on the austenite grain boundaries in weld bond during cooling after welding. Boron addition less than B/N=0.5 promotes the formation of polygonal ferrites, suppressing degenarate pearlite and martensite islands, and decreases the free nitrogen of weld bond, and consequently notch toughness is largely improved. However, excess boron addition (B/N>0.5) produces degenerate pearlite and or martensite islands and deteriorates the toughness. The role of low silicon content is to reduce the formation of martensite islands by replacing pearlitic reaction and this also improve the toughness of weld bond. The newly developed low Si-Cu-Ni-Mo-V-B steel which has 60kg/mm2 grade tensile strength shows very excellent notch toughness at the weld bond after large heat input welding.
  • Formation and Growth Kinetics of Intermediate Phases in Hot Dip Galvanizing

    pp. 2215-2223

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    Iron specimens have been immersed in molten zinc containing no aluminum at temperatures of 430 and 460°C. Intermediate phases appear in the order of ζ (FeZn13), palisade δ1 (FeZn7), Γ (Fe3Zn10), Γ1 (Fe5Zn21) and compact δ1 (FeZn7) phases. This order agrees completely with that observed in the reaction of iron with solid zinc. The reciprocal of the appearance time of each phase has an Arrhenius type of temperature dependence in the temperature range from 240 to 46°C.
    When new phase appears, the growth rates of the phases which have existed prior to the appearance of the new phase vary complicatedly. A side from these variations, the palisade δ1 phase layer grows rapidly twice after the formation of Γ phase and the following formation of compact δ1 phase. It appears that the growth of all phases could not be represented by a simple exponential function.
    EPMA line analysis reveals that the concentration gap between compact δ1 layer and palisade δ1 layer becomes gradually obscure with the increase in width of total δ1 phase layer. It seems that the concentration gap between both δ1 layers is merely the steep concentration gradient derived from the concentration dependence of interdiffusion coefficient in δ1 phase.
  • Study on CaS-Dispersed Steel Produced by Spray-Dispersion Method

    pp. 2224-2233

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    An investigation has been made to make clear the condition for making a fine and homogeneous distribution of sulfide particles in steel which was made by Spray-Dispersion Method. Tensile properties of these steels have also been studied.
    The results obtained are summarised as follows;
    1) A homogenious distribution of fine sulfide particles is made by the addition of Zr or Ce (named distribution controlling element) in steel which has large standard free energies of sulfides formation (-ΔG°).
    2) Mean particle diameter decreases with an increase of Zr or Ce content in steel and fine sulfide particles of less than 800Å are dispersed in 0.5 at pct zirconium-steel or 0.5 at pct rare earth-steel.
    3) Tensile strength and 0.2% proof stess of steel increase with the volume fraction of fine dispersed particles of less than 800Å.
    4) CaS-dispersed steels show larger work-hardening properties and elongation in tensile test than those of oxide-dispersed ones.
  • Determination of Nitrogen in High Carbon Ferrochromium by Graphite Capsule Method

    pp. 2234-2238

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    A vacuum fusion method was used for determination of nitrogen in high carbon ferrochromium by means of a graphite capsule method. Comparisons of metal baths, grain size and grain states of colors were investigated. Nickel, Platinum and Cerium alloys of these metals were used as metal baths for promoting complete extraction of nitrogen from the sample. Best results were obtained when 0.4g of sample and 0.8g of Platinum-Cerium (6%) alloy were enveloped in a degassed graphite capsule and were extracted nitrogen at 1850°C for 20min in the apparatus used. Sample grains were manually fractionated by their surface color and were determined nitrogen with both conventional and the capsule method using PlatinumCerium alloy as bath metal. Black fraction gave nitrogen values as high as 0.038%, while white one gave 0.024%. Dependence of nitrogen value on grain size was detected. Compalative determination were made for nitrogen in the sample of 200-280 mesh size with this method, two chemical methods (Maekawa method and SnCl2-polyphosphoric acid method), an oxidizing fusion method and an inert gas fusion method. The nitrogen values obtained by these methods were 0.036%, 0.029%, 0.031%, 0.024%, 0.027%, respectively. The best result was assumed to be the highest one, because all of these methods were suffered from negative inclinations.
  • Recent Developments of Steelmaking Technology and the Situation of Special Steels in Japan

    pp. 2239-2246

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  • Present State and Future of Railway Rails

    pp. 2247-2256

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  • Properties of Coal and Metallurgical Coke

    pp. 2257-2265

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  • Report of Transportation Committee of the Joint Research Society of ISIJ

    pp. 2266-2273

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    [in Japanese]
  • 報告

    pp. 2274-2292

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  • 誌上討論

    pp. 2293-2293

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  • 第95回講演大会討論会報告

    pp. 2294-2301

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  • 抄録

    pp. 2302-2305

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