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

Tetsu-to-Hagané Vol. 78 (1992), No. 11

  • The Recent Trends of Steelmaking Process with Special Attention to Refractory Technology

    pp. 1625-1634

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    [in Japanese]
  • Development of Textures and Microstructures in Low Carbon Steel

    pp. 1635-1643

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  • Cooperative Tests on Crack Initiation and Crack Propagation in Stress Corrosion Environment

    pp. 1644-1649

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    [in Japanese]
  • Basic Design of Prereduction Fluidized Bed for Smelting Reduction Based on Fluidization and Reduction Characteristics of Iron Ore Fines

    pp. 1650-1657

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    In order to develop the prereduction fluidized bed for smelting reduction process, the fluidization and reduction characteristics of iron ore fines with a wide size distribution, such as sinter feed, were examined. As a result, if the superficial gas velocity is kept over than 2 or 4 times of minimum fluidizing velocity, the segregation of coarse particles can be avoided, and it became clear that the appropriate mean residence time to produce prereduced iron ore of about 20-25% reduction degree was from 30 to 60 minutes. On the basis of these results, a hot model of fluidized bed were so designed that the residence time of fine particles could be controlled by the circulating device, and the characteristics of this hot model were experimentally confirmed. Then, the simulation model considering the elutriation rate of fine particles was made to estimate the operating condition. Furthermore, with the analysis by two-phase model, it was found that the gas interchange coefficient has little influence on reduction behavior, and the fundamental design of the distributor for prereduction fluidized bed was investigated.
    x

    Readers Who Read This Article Also Read

    1. CO2 Recycling for a Carbon Resource Tetsu-to-Hagané Vol.78(1992), No.8
    2. Reaction Rate of Methane Formation for the Catalyst of Reduced Iron Pellets Tetsu-to-Hagané Vol.78(1992), No.11
    3. Outlook of Kinetic Studies on the Combustion of Pulverized Coal in a Blast Furnace Tetsu-to-Hagané Vol.78(1992), No.8
  • Reaction Rate of Methane Formation for the Catalyst of Reduced Iron Pellets

    pp. 1658-1665

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    The methane formation reaction plays an important role in the ironmaking and the chemical processes. However, the reaction rate has not been studied enough for the catalyst of porous reduced iron pellets at elevated temperatures and pressures. In this paper, various parameters affecting the rate of the reaction was investigated in the wide ranges of temperature and pressure for clarifying the mechanism and the rate parameters.
    It is consequently found that the reaction rate increased with the increase in the total pressure and the rate was suppressed by carbon dioxide. As for the temperature dependence, the reaction showed the highest rate at about 873 K and the rate decreased in the temperature range over 873 K, because the CH4 formed by the methanation reaction reacted with CO2 to form CO and H2. The effect of the pore structure of reduced iron pellet on the reaction rate can be described by considering the effectiveness factor.
    The apparent activation energy and the frequency factor for the rate of methane formation reaction were determined from the experimental data. The expression of the frequency factor contains pressure dependence.
    x

    Readers Who Read This Article Also Read

    1. Outlook of Kinetic Studies on the Combustion of Pulverized Coal in a Blast Furnace Tetsu-to-Hagané Vol.78(1992), No.8
    2. CO2 Recycling for a Carbon Resource Tetsu-to-Hagané Vol.78(1992), No.8
    3. New Trend of Sensing Technology Tetsu-to-Hagané Vol.79(1993), No.7
  • Solubility of Carbon Dioxide in BaO-BaF2 Melts

    pp. 1666-1673

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    Equilibrium CO2 partial pressures in the systems BaO-BaCO3 and BaO-BaCO3-BaF2 were measured by using the thermo-balance. The results are summarized as follows,
    (1) Dissociation of BaCO3 under PCO2 = 1 atm occurs at 1645 K and the temperature decreases with decreasing the partial pressure of CO2.
    (2) Interaction parameter on the assumption of regular solution for BaO-BaCO3 melts changed from -23 kJ/mol at 1598 K to -15 kJ/mol at 1773 K.
    (3) Gibbs energy of the reaction BaO (melt) + CO2(g) = BaCO3(melt)ΔG°is given by the following relation,
    ΔG°=-0.152T + 279(kJ/mol)
    (4) Assuming that BaO-BaCO3-BaF2 melts behave as the regular solution, the calculated values of solubility of CO2 in BaO-BaF2 melts are fairly in good agreement with measured ones except for those under PCO2 = 1 atm.
  • Rate of Dissolution of Sintered Alumina into Molten Slags

    pp. 1674-1681

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    The dissolution rate of alumina was calculated from the decreasing rate of radius of a cylindrical specimen dipped into CaO-SiO2-Al2O3 (BF-type) or Na2O-SiO2 slags. The effects of revolution speed, temperature and slag composition on the dissolution rate were examined. The results are summarized as follows;
    (1) The dissolution rate increased with increasing revolution speed. From this result, the dissolution rate was concluded to be limitted by mass transport in slag.
    (2) The apparent activation energies of mass transport in BF-type and soda-silicate slags were calculated to be 186 and 113 kJ·mol-1, respectively.
    (3) From the EPMA analysis of specimen after experiment, it was observed that some slag penetrated into grain boundary of alumina specimen and a CaO·6Al2O3 compound was produced for CaO-SiO2·Al2O3 slag, but that neither penetration layer nor compound are formed for soda-silicate slags.
  • Slag Foaming in Reaction between Molten Slag Containing Iron Oxide and Iron of High Carbon Concentration

    pp. 1682-1689

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    Slag foaming was directly observed in a CaO-SiO2-Al2O3-FeO slag and Fe-C alloy (C = 4.5 mass%) system using a high temperature X-ray radiographic technique at 1773 K. The foaming behavior was characterized by measuring the index of foaming power <κ1>, the foam life <τ>, the bubble diameter of CO gas <dB>, the CO gas evolution rates during the observations and the wettability between the slag and metal.
    The results obtained in the present study were as follows: The index<κ1>; and the foam life <τ> were found to be almost constant during the observations, then the slag foaming behaviour in the system was described by Ito-Fruehan's equation. A small amount of sulphur addition to the system remarkably reduces the CO gas evolution rates. The sulphur addition increases bubble diameter <dB>, which results in the reduction of <κ1>and <τ>. Then the sulphur addition drastically reduces the slag foaming in this system. Therefore, the adjustment of sulfer concentration in the system is one of the most important points for controlling the slag foaming.
    Main cause for the increase in the bubble diameter <dB> can be explained from the increase in the contact angle <θ> between slag and metal by the sulphur addition.
  • Influence of Oxygen Feeding Rate on Simultaneous Removal of Silicon and Phosphorus in Hot Metal

    pp. 1690-1696

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    Removals of silicon and phosphorus from hot metal with lime based flux simultaneously have been studied in the experiment of 100 kg scale.
    Results obtained in this work are as follow:(1) Silicon content of hot metal at which simultaneous removal of silicon and phosphorus can proceed increases with an increase of feeding rate of oxygen. (2) When oxygen feeding rate is more than 0.88 Nm3/min·t, dephosphorization can proceed even if with low basicity slag like CaO/SiO2 of 2. (3) To proceed simultaneous removal of silicon and phosphorus effectively, it is very important to keep high values of oxygen feeding rate and oxygen potential at slag-metal interface.
    Oxygen feeding to top slag is specially effective for increasing an oxygen potential of slag-metal interface.
  • Effect of Oxide Particles on MnS Precipitation in Low S Steels

    pp. 1697-1704

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    The behavior of MnS precipitation on oxide particles in low sulphur and low carbon steels was investigated to control the size and the distribution of MnS. The distribution of MnS became uniform by the complex deoxidation with Mn-Si-Zr, of which complex oxides dispersed finely. On the other hand, in the case of carbon deoxidation in vacuum melting, MnS precipitated less uniformly in interdendritic regions. The precipitation ratio of MnS on oxide particles was higher in the cases of Mn-Al, Mn-Si and Mn-Si-Zr deoxidations, but it depended on the oxide composition. Higher precipitation ratio was obtained in the composition range of MnO-SiO2 where liquidus temperature is low and sulphide capacity is high. The small MnS embryo formed on the surface of the liquid oxide according to its solubility limit may act as a nucleus for the further growth of MnS due to diffusion after the solidification of steels.
  • Consolidation Behavior of Pre-sintered Ferrous Metal in Pseudo-HIP

    pp. 1705-1712

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    Consolidation behavior in pseudo-HIP ( known also as Ceracon) is experimentally investigated using pre-sintered iron-based alloy as a specimen. Pressure transmitting medium is spherical powder of alumina mixed with 5 wt% graphite. Heating temperature is 800-1200°C and pressure of upper punch is 34.7-347 MPa. Obtained results are as follows : Transmitting ratio of applied pressure in the pressure transmitting medium is low and the pressure applied on a specimen is about 1/2 of the applied pressure by upper punch. Maximum density of a specimen achieved is 99.2%. In the range of less than this value, consolidation behavior can be described by the pressure-density equation presented by Shapiro et al. The achieved density in pseudo-HIP is nearly equal to that in HIP, but according to the observation in SEM, the matrix of the cross section of the specimen in pseudo-HIP seems to be less purified than that in HIP. This is because of the difference of consolidating time between in both processes, that is, as the consolidating time in pseudo-HIP is shorter than in HIP, the diffusion of atoms in pseudo-HIP seems to contribute hardly to the increase of the density. Finally, in order to produce a consolidated part of high accurate dimension and good shape, precise setting of a specimen in the die is important.
  • Graphite Pollution Mechanism at the Steel Surface on Annealing of Cold Rolled Open-coil

    pp. 1713-1720

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    On open-coil annealing of cold rolled steel sheet in HNX gas, the gas composition in the furnace are analyzed. On heating, CO, CO2 and hydrocarbons are generated in the atmosphere by combustion and vaporization of the lubricant on the sheet surface. In order to simulate the open-coil annealing, a steel sheet is annealed in CO-CO2-8%H2-N2. Then, the graphite and cementite are formed on the sheet surface. The graphite pollution on the steel surface can be reproduced by the simulative annealing, because the morphology of graphite by the simulative annealing is same as the formed by the open-coil annealing. According to the addition of CO2 in CO-8%H2-N2 atmosphere, the graphite increases incipiently and then decreases, and more addition than the critical CO2 content, which is affected with CO2/CO, suppresses the formation of graphite perfectly. From these results, the graphite on steel surface by annealing in HNX gas atmosphere are formed by the decomposition of CO, and the lubricant for cold rolling is one of the carbon source.
  • Effect of Manufacturing Process on Properties of Forge-quenched Bevel Gear after Caburizing

    pp. 1721-1728

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    The effects of varying manufacturing process parameters on the properties of a forge quenched bevel gear after carburizing were examined.
    The microstructure, height (L) to diameter (D) ratio of preform, holding time at quenching temperature and corner radius of tooth root were studied.
    The following results were obtained (1) Matrix structure of tooth root of gear forged at 850 and 950°C was dual phase structure of martensite and ferrite. The fatigue properties have been correlated to this dual phase structure. (2) Suitable L/D ratio of preform was 1.0. (3) Recrystallization of austenite after forging began at 10 sec and finished at 30 sec. (4) The bending fatigue limit of the corner radius of tooth root was increased 20% by changing from 0.5 mm to 1.0 mm and was 60% higher than the conventionally processed gear.
    The results of these tests have led to the development of super fatigue strength bevel gears.
  • Assessment of Creep Crack Growth Behavior of Service-degraded 2 1/4 Cr-1Mo Cast Steels

    pp. 1729-1736

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    Creep crack growth behavior was experimentally investigated at 570°C in 2 1/4Cr-1Mo cast steels, taken out of heavy section components in power boiler plants of which the total service life were longer than 100000 hours. Stress intensity factor, load line displacement rate, C* -integral andQ* -parameter were used as parameters to evaluate the creep crack growth rate. And, degradation of crack growth in aged materials was observed in the evaluations.
    In the relationship ofC* -integral or load line displacement rate, and the creep crack growth rate, the so-called tail part, which characterizes the early stage of the test owing to the transient behavior, was considered. The relationship between the minimum of load line displacement rate and fracture life fell on practically a single trend line in terms of Monkman-Grant type equation. It means that the equation is found to be of activation type.
    At last, the softening region near crack tip was discussed in the relation of the crack growth resistance.
  • The Effect of V and W Addition on the High Temperature Strength Properties of 12%Cr-15%Mn Austenitic Steels

    pp. 1737-1744

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    The effect of W and V on the high temperature strength properties of 12% Cr-15% Mn austenitic steels was studied from the view point of precipitation hardening and internal stress. The contribution of W addition to the tensile and creep-rupture strength was not so large. By contrast the combined addition of W and V increased the strengthes considerably. These are resulted from the precipitation of fine vanadium nitride (VN) within grains and the enhancement of M23C6 type carbide precipitation at grain boundaries. The V added material had large internal stress value which is considered to be due to dislocation movement disturbed by fine vanadium nitrides.
  • Precipitation and Growth of δ Phase in Ni-l5Cr-8Fe-6Nb Alloy

    pp. 1745-1752

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    The precipitation and growth behaviors of δ phase in Ni-base superalloy, modified Inconel X-750 type alloy ( X-750 M), have been investigated mainly by opticaland transmission electron microscopy.
    The morphology, the crystallography and equilibrium transformation temperatures of the cellular and the Widmanstätten precipitation of γ phase to δ+ γ phases have been discussed.
    The obtained results are as follows:
    (1) The hardness of X-750 M aged in various conditions closely related to the size and the quantity of γ" and δ precipitates.
    (2)The orientation relationship between γ and δ phase in the cellular and the Widmanstätten precipitates was:
    {111}γ//{010}δ <110>γ//<100>δ.
    (3) The interlamellar spacing in each precipitation mode was inversely proportional to the degree of undercooling below the equilibrium transformation temperature of γ phase to δ+ γ phases.
    (4) According to the theory of diffusion controlled eutectoidal growth, the equilibrium transformation temperatures of the cellular and the Widmanstätten precipitation were estimated to be 1279 and 1313 K, respectively. These temperatures were consistent with the experimental tendency.

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