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

Tetsu-to-Hagané Vol. 80 (1994), No. 7

  • Kinetic Analysis on Gaseous Reduction of Agglomerates, Part 2, Rate Parameters Included in the Mathematical Model for Gaseous Reduction of Agglomerates

    pp. 493-500

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  • Activities of Constituents in FeO·Cr2O3-MgO·Cr2O3 Spinel Solid Solution

    pp. 501-506

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    The activity of iron chromite in solid FeO·Cr2O3-MgO·Cr2O3 spinel, saturated with Cr2O3, was determined at 1573 K, by the equilibrium measurement of iron dissolved in liquid silver held in the spinel crucible with CO-CO2 gas mixture, to clarify the thermodynamic properties of chromium ores used in ferrochromium industry.
    The solubility of Cr2O3 in FeO·Cr2O3-MgO·Cr2O3 spinel phase was found to be negligibly small. The free energy of formation of FeO·Cr2O3 was determined as follows;
    Fe (s) + 1 / 2O2(g) +Cr2O3 (s) = FeO·Cr2O3 (s),
    ΔG0 =-307600 + 66.82 T (J/ mol).
    (1423-1723 K)
    The activities of constituents in FeO·Cr2O3-MgO·Cr2O3 spinel solid solution coexisted with Cr2O3 showed negative deviation from ideality. It was observed that the spinel solid solution took regular solution behavior, and α-function of FeO·Cr2O3-MgO·Cr2O3 system was determined as follows;
    αFeO·Cr2O3 = RTlnγFeO·Cr2O3 / (1-NFeO·Cr2O3) 2MgO·Cr2O3 = RTlnγMgO·Cr2O3/(1-NMgO·Cr2O3 ) 2=-12800 (J).
  • Complex Oxides between BaO and CrOx at an Oxygen Partial Pressure of 0.25 Atm

    pp. 507-508

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  • Rough Estimation of Viscosity for Multicomponent Silicate Melts

    pp. 509-514

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    A method of approximate prediction of the viscosity of multicomponent silicate melts was proposed in view of practical use, on the basis of the relationship between the network parameter deduced from the viscosity of melts and the anion-cation attraction parameter. It was postulated in the method that the anion-cation attraction parameter is considered to be melt-structure (or polymerization)-dependent. The generalized relationship exists between the network parameter and the modified anion-cation attraction parameter.
    In order to check the validity of the above estimation method, viscosity data for multicomponent silicate melts have been collated. Theoretical values based on the method show excellent agreement with the experimental data.
  • X-ray Fluoroscopic Observations of Bubble Characteristics in a Molten Iron Bath

    pp. 515-520

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    The formation of bubbles at the nozzle exit and the subsequent rising behavior of the bubbles in a molten iron bath at 1250°C were observed using a high voltage X-ray fluoroscope and a high-speed video camera. The frequency of bubble formation at the nozzle exit, the mean bubble diameter, and the mean bubble rising velocity were obtained for a wide range of the injected argon gas flow rate. Empirical correlations of these quantities were proposed and compared with previously published data and empirical correlations.
    It has been commonly believed that the frequency of bubble formation at the nozzle exit depends solely on the gas flow rate and the outer diameter of the nozzle when the gas flow rate is relatively high and the wettability between the nozzle material and the molten metal is bad. The present experimental results revealed that the frequency of bubble formation had a close relationship not with the outer diameter but with the inner diameter of the nozzle. Also, the bubble frequency depended on the gas flow rate and the physical properties of gas and molten metal. The critical gas flow rate for the initiation of smaller bubbles due to disintegration of larger bubbles was found to be approximately 60cm3/s under the present experimental conditions. The bubble behavior near the bath surface also was made clear.
  • Kinetics of Decarburization Reaction of Molten Steel with CO Bubble Evolution in Pressure Decreasing Stage

    pp. 521-526

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    The dominant factors of the carbon removal reaction from a molten steel with an Ar injection stirring under the pressure decreasing stage have been studied using a vacuum tank degassing furnace containing 7 ton melt.
    1) The decarburization rate constant, kc', increased with the increase in the pressure decreasing rate and with the increase in an oxygen content.
    2) The vigorous CO bubble evolution in the molten steel was observed in the pressure decreasing stage. So, the CO bubble evolution rate constant, kCh and the super-saturation pressure, Pco*, for the CO bubble evolution were taken into consideration in a decarburization reaction model. The decarburization behaviors were simulated successfully by the reaction model.
    3) The value of kCh increased with the increase in the Ar injection flow rate, and the value of Pco* was estimated to be 22.525.0 mmHg.
    4) In the pressure decreasing stage, the decarburization reaction was divided into three types, namely, a) an evacuating control, b) a stirring control and c) a mixed control of evacuating and stirring. In order to increase the decarburization rate, it is essential to keep a high oxygen content, to evacuate fast and to supply enough stirring to a molten steel according to the evacuating rate.
  • Motion of Small Particles in Solution with a Interfacial Tension Gradient and Engulfment of the Particles by Solidifying Interface

    pp. 527-532

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    In order to clarify the behavior of small non-metallic inclusions and bubbles in liquid steel in front of an advancing solid-liquid interface, the force acting on a particle, and the velocity of the particle, due to the interfacial tension gradient between particle and solution, were investigated theoretically and experimentally. The force and the velocity are theoretically described as a function of particle radius, viscosity of solution and interfacial tension gradient. The velocity of small bubbles in a water solution with C18H29SO3Na concentration gradient was observed. The theoretical equation derived in this paper can describe experimental results of the velocity. The critical solidifying velocity from particle pushing to engulfment by the interface was evaluated qualitatively by combining the effect of interfacial tension gradient induced by concentration and temperature gradient formed in boundary layer in front of the solid-liquid interface with the treatments developed by the previous investigators based on the wettability of the particle with the solid and liquid.
    x

    Readers Who Read This Article Also Read

    1. Behavior of Non-metallic Inclusions and Bubbles in Front of Solidifying Interface of Liquid Iron Tetsu-to-Hagané Vol.80(1994), No.7
  • Behavior of Non-metallic Inclusions and Bubbles in Front of Solidifying Interface of Liquid Iron

    pp. 533-538

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    The velocity of small particle caused by interfacial tension gradient in the boundary layer of concentration formed in front of an advancing solid-liquid interface is derived as follows:
    V1 = (4/9ηDL) (1-KE) Co (dσ/dCL)RVS × [1+ (9/8)R/ (x-R)]-1exp[-Vs (x-δ)/DL]
    Using the equation, the behavior of Al2O3 inclusions and bubbles in the boundary layer of concentration of Fe-O, Fe-Ti, Fe-S systems was analysed and clarified in relation to solidifying velocity, bulk flow of the liquid iron and solute concentration as well as radius of inclusion or bubble. The analyses predict that the small Al2O3 inclusions or bubbles move toward and contact solidifying interface due to the concentration gradient of the solute O, Ti, S and the velocity of the inclusions and bubbles increases with increase of the concentration of the solutes O, Ti and S.
  • Effect of Initial Total Oxygen Concentration on the Rate of SiO2 Inclusion Removal from Molten Cu

    pp. 539-544

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    The effect of initial total oxygen concentration, [mass%O]T0, on the rate of inclusion removal from molten copper has been investigated.
    Under the mechanical stirring condition, it is found that the rate constant of inclusion removal, ko, is independent of the rotation speed of stirrer, whereas it is dependent on [mass%O]T0. From the results of microscopic observation of inclusion particles with SEM, size distribution of inclusion particles is obtained. The rate constant, ko, increases with increasing initial value of particle number density and mean radius of inclusion particle. The change in ko with the initial content of inclusion in the metal phase can be interpreted in terms of coagulation of inclusion particles.
    Under Ar gas injection stirring condition, ko increases with increasing gas flow rate, while it does not apparently depend on [mass%O] T0. In the case of Ar gas injection stirring condition, the effect of coagulation on the rate of inclusion removal is smaller than that under the mechanical stirring condition. It is considered that the inclusion particles are removed from the melt mainly through adhesion to the gas bubble-metal interface.
  • Effect of P Content in Ultra Low C-Ti Steel on Galvannealing Behavior

    pp. 545-550

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    An investigation was made on the effects of the P content on Γ phase growth during the process of galvannealing ultra-low-carbon-0.05%-Ti-steel sheet. The results showed that a P content of equal or more than 0.025% tends to suppress the growth of the Γphase. With a low P content (0.005%), during the galvanizing process, a relatively small Al concentration is detectable at the interface between the Zn coating layer and the steel substrate and this accelerates the formation of the outburst structure. With a high P content (0.052%) in which more P is concentrated at the steel surface, the Al concentration in the interface is large. This results in the formation of an Fe-Al alloy layer having a stronger burrier effect of difusion and the outburst structure is significantly suppressed. During the galvannealing of low-P steel, the Γphase begins to grow after the ζ and δ1 phases have developed to some extent. This is because the δ1 phase, constituting mainly the outburst structure, directly contacts the substrate from the stage of the galvanizing process. Thereafter, the iron content of the δ1 phase rises, accelerating the formation of the Γphase. With high-P steel, in contrast, the galvannealing process progresses through the Fe-Al alloy layer, since no direct contact occurs between the δ1 phase and the substrate. The Γphase starts to grow only after the ζ phase disappears, which means the Γ phase growth is delayed.
  • Pattern Recognition of Microstructures using Neural Networks

    pp. 551-556

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    A pattern recognition system for microstructures using neural networks has been developed. The system consists of two neural networks, a feature extraction network and a classification network. The feature extraction network classifies local area patterns of an input image into reference vectors and generates the histgram of the classified vectors. The classification network learns the histgram data of sample images using the back-propagation algorithm and classifies the microstructures into pre-determined categories. The system shows high performance in the classification of graphite shapes in cast irons and of grain sizes of stainless steels.
  • Solid Solution Hardening and Softening of Austenite in Plain Carbon Steel

    pp. 557-561

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    Solid solution hardening and softening of austenite, i.e. completely opposite phenomena, have been reported for plain carbon steel. These problems were studied in tension and compression tests for 0.05 to 0.84 mass % carbon steels. The shapes of dynamic recrystallization (DRX) type flow curves are almost independent of carbon content. Peak flow stress as well as steady state flow stress rapidly decrease with increase in carbon content and approach a certain value in high concentration, i.e. solid solution softening takes place in the range of higher strain. On the other hand, flow stresses in the range of initial work hardening rapidly increase and then go to a saturation, i.e. solid solution hardening occurs at lower strains. The solid solution softening for stresses at higher strain can be attributed to the enhanced DRX caused by increased diffusivity of vacancy due to the addition of carbon. In contrast, the solid solution hardening for stresses at lower strain may be caused by the increase of dragging stress for dislocation motion due to carbon atmosphere or excess vacancy.
  • Effect of Nitrogen in Solution on High Temperature Creep Resistance of High Purity Chromium

    pp. 562-567

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    The effect of solute nitrogen on the high temperature creep resistance of pure chromium has been investigated in argon atmosphere using the specimens aged for 3.6 × 105s at 1273K (200ppm Nitrogen) and as solution treated (without nitrogen). The minimum creep rate of the prior-aged specimen was lower than that of the as solution treated one. The evolution of subgrains during creep was suppressed in the prior-aged specimen compared with the as solution treated one. Stress reduction tests were conducted at the minimum creep rate, in order to evaluate the creep rates under the same subgrain size. Under the same subgrain size, the creep rate of the prior-aged specimen was 1/5 of the as solution treated one. The higher creep resistance of the prior-aged specimen was attributed to the solid solution strengthening due to nitrogen.
  • Effects of Aging and Stress Aging on Creep Resistance of Single Crystal Ni-base Superalloy CMSX-4

    pp. 568-573

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    Influence of the formation of rafted structure of γ' phase on creep resistance has been investigated using a single crystal nickel-base superalloy, CMSX-4. The rafted structure of γ' was controlled by conducting stress aging (creep test) at 1273K-160MPa up to 3.24×106s. Aging without stress, called simple aging, was also performed at 1273K up to 3.6×106s. Cuboidal γ' in the specimen as heat treated turned to the rafted one during a transient creep stage of stress aging. In the simple aging, cuboidal γ' became larger without changing their shape. The stress enhanced creep tests were conducted at 1273K-250MPa to evaluate the creep resistance of the stress aged specimens and the simple aged ones. There was little difference in the minimum creep rate between the simple aged specimens and as heat treated one. But minimum creep rates of stress aged specimens were always larger than those of as heat treated one. The TEM observation of specimens interrupted the stress enhanced creep test at minimum creep rate showed that the stress aged specimens have the γ region partially with high dislocation density which was not detected both in as heat treated specimen and the simple aged ones. The larger minimum creep rate in the stress aged specimens with rafted structure of γ' phase was caused by the increase in the width of the channel of γ matrix.
  • High-Temperature Oxidation of Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si Superalloy in Ar-H2O Atmosphere

    pp. 574-579

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    The oxidation of an Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si alloy, Incoloy 909 type alloy (alloy 909), has been investigated in the temperature range of 1000K to 1400K in Ar-(1, 10%)H2O atmosphere using metallographic, electron probe microanalysis and X-ray diffraction techniques.
    The oxide scales consisted of an external scale and an internal scale which had an intergranular scale (> 1200K) and an intragranular scale. The oxide phases in each scale were identified as α-Fe2O3(< 1200K) or FeO (> 1300K) and CoO·Fe2O3 and FeO·Nb2O5, respectively.
    The morphologies, the oxide phases and the oxidation rates did not depend on the partial pressure of H2O in the range between 1 and 10 percent in Ar gas. The rate constants for the intergranular scale formation in alloy 909 were about one-tenth as large as those in Fe-36%Ni alloy reported previously.
    At all the temperatures the scales grew according to a parabolic rate law and the apparent activation energies for the processes were estimated.
  • Introduction to Solidification of Metals (IV)

    pp. N371-N385

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  • Outlook of Work Rolls in Hot Strip Finisher for Steel Rolling

    pp. N386-N389

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