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

Tetsu-to-Hagané Vol. 79 (1993), No. 12

  • The Kinds of Reactions in Coke Gasification by H2O

    pp. 1305-1310

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    Recently, in order to stabilize the blast furnace conditions, the vapour and/or pulverized coal are injected into blast furnace. The concentration of H2 in blast furnace increases above 8% in such a circumstance. Then it is so important to understand H2 behaviour in blast furnace.
    In this study, gasification reaction of metallurgical coke by Ar-H2-H2O mixtures at 1273, 1473 and 1673K has been investigated. The measurement of reaction rate was carried out with gas analysis method using both of Quadrupole Mass Spectrometer (QMS) and Infrared gas analyser. The gas analysis method is so useful for not only the quantifying the reaction rate but also the estimating the kinds of reactions occurring in H2O-coke gasification. The consideration of the kinds of reactions were made by using the thermodynamic characterization of produced gas composition and the variation of the amount of each produced gases (H2, CO, CO2) according to reaction temperature. The kinds of reactions in the region above 1273K were elucidated.
    In coke gasification by H2O, main reaction is water gas reaction I. The generation of CO2 is caused by water gas reaction II and the possibility of water gas shift reaction is very low. Further, owing to produced CO2, Boudouard reaction occurs and it becomes prominent in high temperature range.
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  • Reaction Mechanism and Kinetic Analysis of Coke Gasification by H2O

    pp. 1311-1316

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    Kinetic analysis of coke gasification by H2O was studied. The reaction mechanism was considered according to the restricting the adsorption site as the carbon having dangling bond at periphery of carbon net plane. The kinds of reactions estimated from reaction mechanism were consistent with the results of gas analysis in gasification experiment. From the reaction mechanism, rate equation which expressed the rate of three kinds of reactions (Water gas reaction I, Water gas reaction II and Boudouard reaction) was proposed.
    That is,
    K=ST (k1-W1PH2O+k1-B PCO2) (1+k1-w2) /1+ K4PH2+k5+PH2O+k2PCO+k3PCO2
    where ST is the dimensionless concentration of adsorption site (or the number of carbon having dangling bond per a carbon atom). k1-W1, k1-B, k1-W2 are rate contant as promotion term of gasification, corresponding to Water gas reaction I, Boudouard reaction and Water gas reaction II, respectively. k2k5 are rate constant as restriction term by each gases. The results of calculation using the rate constants obtained by kinetic analysis have good agreement with the reaction rate but also the produced gas composition.
    x

    Readers Who Read This Article Also Read

    1. Development of "In-situ" Observation System for Oxide Films Formed during Thermal Oxidation Using Raman Spectroscopy Tetsu-to-Hagané Vol.81(1995), No.6
    2. Sintering Process Usiug Pisolite Lumpy Ore as Hearth Layer Tetsu-to-Hagané Vol.80(1994), No.4
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  • Fluidization and Degradation Characteristics of Iron Ore Fines in Prereduction Fluidized Bed

    pp. 1317-1322

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    The integrated test plant, consisting of a prereduction fluidized bed and in-bath smelting furnace characterized by high post combustion, was installed at NKK's Fukuyama Works, and the operation was started in 1988. The prereduction fluidized bed uses iron ore fines as feed, and the fluidizing condition and pressure fluctuation characteristics to keep the stable fluidizing were clarified by the operation of the integrated test plant. The classification behavior of fines was analyzed by the measurement of the elutriation rate constant. Then, the degradation phenomena of iron ore fines were observed during the preheating and prereduction of iron ore fines in the fluidized bed, and it was quantitatively analyzed by the application of Rittinger's law for size reduction. The model including classification and degradation behavior was constructed so as to estimate the operating condition. These results were considered to be availabe in the scale-up of the prereduction fluidized bed.
    x

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    2. Sintering Process Usiug Pisolite Lumpy Ore as Hearth Layer Tetsu-to-Hagané Vol.80(1994), No.4
    3. Rist Operating Diagram(I) Tetsu-to-Hagané Vol.79(1993), No.9
  • Reduction Behavior of Iron Ore Fines and Circulation Characteristics of Finesin in Prereduction Fluidized Bed

    pp. 1323-1328

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    The operation of prereduction fluidized bed combined with an in-bath smelting furnace was performed in NKK Fukuyama Works. Iron ore fines, such as sinter feed are directly charged into the fluidized bed. This fluidized bed was so designed as to form a dense bubbling bed and equip the circulating device. The reduction characteristics of iron ore fines were clarified through the operation in the integrated test plant. According to the above results and the simulation model based on the elutriation behavior, the appropriate residence time of coarse became 30-60 min to reduce the iron ore to 20-25% reduction degree in 800°C bed temperature. The effect of circulation of fines was not quantitatively clear in the test, but the favorable circulation ratio was estimated with a mathematical model. Moreover, it was found that the collection efficiency of cyclone was closely related to the yields of prereduced ore and the circulation ratio influenced on the losses of products.
    x

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    1. Development of "In-situ" Observation System for Oxide Films Formed during Thermal Oxidation Using Raman Spectroscopy Tetsu-to-Hagané Vol.81(1995), No.6
    2. Sintering Process Usiug Pisolite Lumpy Ore as Hearth Layer Tetsu-to-Hagané Vol.80(1994), No.4
    3. Rist Operating Diagram(I) Tetsu-to-Hagané Vol.79(1993), No.9
  • Distribution of Surface Temperature of Molten Titanium by Thermal Plasma

    pp. 1329-1333

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    Surface temperature of molten titanium by thermal plasma was measured by a radiation thermometer. Direct current arc plasma was generated in a transferred type plasma system, in which a tungsten rod was used as a cathode and water-cooled copper plate as an anode. Titanium in column of about 3 grams in weight was melted by argon and argon -35%hydrogen plasma with the electric power of about 400 watts. The surface temperature was measured by a radiation thermometer and it was corrected by emissivity of molten titanium. The emissivity was determined using temperatures measured by a radiation thermometer and a thermocouple.
    The emissivities of molten titanium were 0.33 and 0.25 in argon plasma and argon-hydrogen plasma, respectively. The surface temperature was the highest at the top of molten titanium and went downward steeply far from the top. The highest temperatures were approximately 2800K and 3000K in argon plasma and argon-hydrogen plasma, respectively. High temperature area above 2200K was limited to the area where plasma flame was directly irradiated. The temperature in the other area was approximately 1940K, around the melting point.
  • The Solubilities of MnS in MnO-SiO2-TiO2 Melts

    pp. 1334-1337

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    The solubilities of MnS in MnO-SiO2-TiO2 melts have been investigated to clarify the mechanism of the formation of inclusions in steel during solidification by employing a chemical equilibration technique. A MnS pellet was equilibrated with MnO-SiO2 and MnO-SiO2-TiO2 melts between 1528 and 1723K. The solubility of MnS in MnO-SiO2 melts increases with increasing the ratio MnO/SiO2 and temperature. The influence of replacement of SiO2 by TiO2 on the MnS solubility of the MnO-SiO2-MnO-TiO2 system has also been investigated at 1623K. The solubility of MnS increases with increasing TiO2 content. Furthermore, the precipitation mechanism of oxysulfide inclusions during solidification of steel is discussed.
  • Mathematical Models for Set-up Control System in H-beam Universal Rolling

    pp. 1338-1344

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    It is well known that universal rolling of H-beam shows complicated behaviors of metal flow between web and flange, multiplication of roll separating force and complex distribution of temperature in comparison with flat rolling.
    Because of these complex rolling characteristics, there is a limit of dimensional accuracy in manual control by operators. An automatic roll gap control system is necessary to obtain high productivity and high dimensional accuracy of H-beam.
    Authors developed the mathematical models for this control system of universal rolling as following procedure.
    (1) Rolling temperature model
    The distribution of temperature in the cross section of H-beam is computed by the finite difference method. Then the simplified mathematical model has been developed to predict the mean temperature of both web and flange during rolling based on these results of the computation.
    (2) Roll separating force model and flange width spread model
    Lead model rolling experiments have been performed in various rolling conditions of reduction ratio, thickness and flange width. From these works, the models to predict the flange width spread and roll separating force have been obtained as the function of the rolling conditions which are mainly the geometrical size of H-beam.
    Due to application of these models to set up control, high dimensional accuracy of H-beam has been obtained.
  • Superplasticity of Low Carbon HSLA Steel during Bainite Transformation

    pp. 1345-1349

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    Transformation plasticity related to the bainitic transformation during continuous cooling with applied stress up to 190MPa in a low carbon HSLA steel was studied. The effect of superplastic deformation on microstructure and tensile properties was also examined. The obtained results are as follows :
    (1) Bs and bainite trasformation range were shifted to a higher temperature with increasing of applied stress above about 60MPa.
    (2) Bainitic structure consisted of lath-like bainitic ferrite and granular bainitic ferrite. An increase of applied stress decreased the former and the structure at 190MPa of applied stress was almost granular.
    (3) For stresses above about 50MPa superplastic strain was greater than linear function of applied stress.
    (4) Superplastic deforming in the bainite transformation did not change the tensile properties in tests at room temperature and -196°C.
  • Development of {100} Texture in Silicon Steel Sheets by Isothermal Austenite→Ferrite Transformations and Its Mechanism

    pp. 1350-1355

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    An investigation has been made to develop {100} texture in silicon steel sheet by an isothermal austenite (γ) →ferrite (α) transformation. Steel sheets alloyed with approximately 2% of silicon, 1% of manganese and 0.1% of carbon were vacuum-annealed and then decarburized in a 20% hydrogen-argon atmosphere containing water vapor. During the vacuum-annealing at the α/γ duplex-or γ-phase temperatures from 900 to 1050°C, a thin layer just below the surface of the sheet transformed to α-ferrite and a strong texture of {100} <011>or {100} <ovw>type developed in the layer. By the subsequent decarburization, the α-ferrite grains in the layer grew toward the thickness center of the sheet, forming a columnar grain structure. The resulted columnar grain structure that inherited the texture of the surface α-ferrite layer exhibited an excellent soft-magnetic properties. The γ→α transformation within the surface layer is considered to be due to a long-range carbon diffusion induced by a manganese dilution in the layer. The selective driving force for the strong {100} texture formation is thought to reside in the anisotropy of the surface energy at the annealing atmosphere-metal interface.
  • Production of Superalloy Powders by means of Confined Design Gas Atomization with Supersonic, Multiple Discrete and Swirl Jets

    pp. 1356-1362

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    For developing a fine superalloy powder production process, a steelmaking pig iron instead of the superalloy as atomizing metal was selected from reasons of economy and availability, and effects of some gas jet streams of a confined design gas atomization on mass median particle diameter of the iron powder were studied. The application of streams of swirl jet, multiple discrete jets and supersonic jet to the atomization was more effective for disintegration of the iron melt. In addition, the disintegration phenomena were observed using a video camera and the atomization mechanism was discussed.
    On the basis of these results, a confined design gas atomization process with supersonic, multiple discrete and swirl jets was developed. By using this process, a fine Co based superalloy powder of about 30 μm in mass median particle diameter was produced.
  • Precipitation and Growth of γ' Phase in Fe-38Ni-13Co-4.7Nb Superalloy

    pp. 1363-1368

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    Fe-38Ni-13Co-4.7Nb base superalloy (alloy 909) is the latest low thermal expansion chromium-free superalloy with a good resistance to SAGBO (Stress Accelerated Grain Boundary Oxidation) embrittlement at elevated temperatures. This investigation was carried out to elucidate the relation between the age-hardening and the nucleation and growth behavior of γ' precipitates in alloy 909 by micro Vickers hardness test and transmission electron microscopy. The results obtained in this study are as follows :
    (1) The hardness of alloy 909 measured at aging temperatures was ca. HV100 lower than that measured at room temperature.
    (2) The hardness of specimens aged at 893-1033K for durations up to 720ks closely related to the mean size of γ' precipitates.
    (3) The growth kinetics of the γ' precipitates in ε phase free region was explained by Lifshitz-Slyozov-Wagner's theory of volume diffusion controlled growth at 943-1033K. The activation energy for the growth of γ' precipitates was estimated to be 254kJ/mol which was nearly equal to those of diffusion of Ti or Fe atoms in γ-iron or nickel.
  • Morphology of γ'' Precipitates in Ni-15Cr-8Fe-6Nb Alloy

    pp. 1369-1373

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    The morphology of γ''precipitates extracted from a nickel-base superalloy, a modified NCF 3 type alloy (X-750M), was investigated mainly by transmission electron microscopy (TEM). The TEM images using carbon extracted replica of γ'' precipitates were clearer than those using electropolished thin film. The γ'' precipitates were disc shaped in the early stage of aging and became elliptic or irregular shaped plates in latter at up to 1033K, while they grew in rectangular shaped plates in latter at 1073K. Many of larger γ'' precipitates in the specimens aged at up to 1033K exhibited a considerable amount of internal fringe contrast. Selected area diffraction pattern from them showed continuons streaks normal to {112}γ''. The internal contrast is thought to be due to stacking faults. The internal fringe contrast was not observed in γ'' precipitates in the specimen aged at 1073K.
  • Effect of Fretting on Fatigue Strength of a Ti-6Al-4V Alloy under a Number of Environments

    pp. 1374-1379

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    Differences in the effect of fretting on fatigue behaviors of annealed and STA heat treated Ti-6Al-4V alloys, whose β phase volume is 15% and 60%, respectively has been studied under a number of environments and discussed in relation to differences in friction coefficient, main crack initiation site at the fretted area, paring of micro cracks by pad, crack growth rate, corrosion pit initiation site and microstructures.
    The saturation of fretting fatigue damage occurs beyond a certain number of fretting cycles. The ratio of the smallest number of fretting cycles to the fretting fatigue life for the saturation to occur in air is more than 90%, and that in pure water is about 50% in the STA alloy, but in the annealed alloy that in chloride-containing methanol is almost 0%. The fretting fatigue strengths are lower than the fatigue strengths in air, synthetic sea water, etc. However, in chloride-containing methanol, the fretting fatigue strength is the same as the fatigue strength in the annealed alloy, but the former is higher than the latter in the STA alloy.
  • Critical Review of the Inclusion Rating by JIS-G-0555 Method and New Inclusion Rating Based on Statistics of Extreme and Its Applications

    pp. 1380-1385

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    It is shown that conventional standards for inclusion rating such as ASTM method and Japanese Industrial Standard (JIS method) are no longer useful for the evaluation of inclusions contained in recent clean steels. A new inclusion rating method based on the statistics of extreme is proposed.
    Inclusion ratings on two kind of super-clean bearing steels, SUJ2 (N) and SUJ2 (H) were done by JIS method and the method based on the statistics of extreme and the results were compared. Total oxgen contained in SUJ2 (N) was 8ppm and that in SUJ2 (H) was 5ppm. No clear difference was obtained by JIS method between the inclusion ratings of SUJ2 (N) and SUJ2 (H). If we define the size of the maximum inclusion in a standard inspection area by the square root of projection area, √areamax, the distribution of √areamaxobeys the statistics of extreme.
    The method based on statistics of extreme can distinctly discriminate even the slight difference in cleanliness between SUJ2 (N) and SUJ2 (H). Moreover, the method of statistics of extreme enables one to predict the size of the maximum inclusion which is expected to be contained in larger area or volume than inspected area.
    The value of √areamax can be also used for the prediction of scatter band of fatigue strength of high strength steels. The agreement of the prediction and experiments on the scatter band of fatigue strength of SUJ2 (N) and SUJ2 (H) is shown.

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