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

Tetsu-to-Hagané Vol. 77 (1991), No. 4

  • Future Production of Blast Furnace Coke at Lower Temperature

    pp. 471-479

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    Readers Who Read This Article Also Read

    1. Circulation and Reduction Behavior of Iron Ore in Circulating Fluidized Bed Tetsu-to-Hagané Vol.78(1992), No.7
    2. Analysis of Steam Flow in Coke Oven Chamber Tetsu-to-Hagané Vol.77(1991), No.8
    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8
  • Progress of Technology in Powder Transportation

    pp. 480-489

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    Readers Who Read This Article Also Read

    1. Circulation and Reduction Behavior of Iron Ore in Circulating Fluidized Bed Tetsu-to-Hagané Vol.78(1992), No.7
    2. Analysis of Steam Flow in Coke Oven Chamber Tetsu-to-Hagané Vol.77(1991), No.8
    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8
  • The Phase Relations of the CaO-MnO-SiO2 System in Connection with the Smelting Reduction of Manganese Ore

    pp. 490-495

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    The phase relations of the CaO-MnO-SiO2 system at 1400°C have been investigated in connection with the smelting reduction of manganese ore in a basic oxygen furnace by employing a chemical equilibration technique. Namely, a molten Cu-Mn alloy was separately equilibrated with a CaO-MnO solid solution or a CaO-MnO-SiO2 melt. It has been found that the solid in conjugation with the molten phase is nearly pure MnO regardless of the composition of the latter. The CaO-MnO solid solution negatively deviates from an ideal solution. From these findings, the dissolution behavior of manganese ore into a molten slag has been discussed.
  • Theoretical Analysis and Model Experiment on Melting Salts by Use of a Direct Induction Skull Melting

    pp. 496-503

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    A direct induction skull melting which was developed for melting materials with high electric conductivity at liquid state and with low one at solid state is one of skull meltings by use of high frequency induction heating. This process has the advantage of melting and holding the high melting temperature materials or chemically active ones without contamination from a crucible. It also has higher energy efficiency than that of the cold crucible which has the same advantage concerning melting without contamination from a crucible. In this melting the skull existing between coil and melt plays roles of electrical, chemical and thermal insulators so that control of the skull thickness is important. By conducting model experiments using NaCl, KCl and CaF2 as a charge, it has been found that the system stability depends on the convection which governs temperature distribution in the melt. By developing a one dimensional thermal transfer model in radial direction, the conditions for getting a stable skull have been studied and the relation between the magnetic and cooling conditions needed for the stable operation has been derived.
  • Copper Distribution between FeS-Na2S Flux and Carbon Saturated Liquid Iron

    pp. 504-511

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    Copper distribution between FeS-NaS0.5 flux and carbon saturated liquid iron has been studied at 1673 K. Copper distribution ratio, LCu=(mass%Cu)flux/[mass%Cu]iron, was about 9 when FeS only was used as sulfide flux. The addition of NaS0.5 to FeS increased the copper distribution ratio. The LCu showed the maximum value of about LCu=24, at around XNaS0.5=0.4, and became nearly constant at the range of higher NaS0.5 content than 0.4 of NaS0.5. The addition of NaS0.5 also lowered sulfur content in liquid iron from 1.9 mass% at XNaS0.5=0 to 0.04 mass% at XNaS0.5=0.8. CuS0.5 dissolved in flux decreased LCu at high concentration range of NaS0.5.
    In order to discuss the effect of NaS0.5 and CuS0.5 on the copper distribution, the activity coefficient of CuS0.5 in flux was evaluated. It was found that NaS0.5 decreased the activity coefficient of CuS0.5 in flux, so that the LCu increased in spite of the significant decrease of sulfur potential in the system by the addition of NaS0.5.
  • Electron Beam Melting of Sponge Titanium

    pp. 512-519

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    Fundamental investigations were done on electron beam melting of sponge titanium by using 80 kW electron beam melting furnace. Results obtained are as follows:
    (1) To increase the melting yield of titanium in electron beam melting of sponge titanium, it is important to recover splashed metal and to prevent the evaporation of molten metal during melting. It is possible to collect the splashed metal by installation of water-cooled copper wall around the hearth and to decrease the evaporation loss of titanium by keeping the surface temperature of molten metal just above the melting temperature of titanium without local heating.
    (2) Specific power consumption of drip melting of pressed sponge titanium bar and hearth melting of sponge titanium are approximately 0.9 kWh/kg-Ti and 0.50.7 kWh/kg-Ti respectively.
    (3) Ratios of the heat conducted to water-cooled mould in the drip melting and to water-cooled hearth in the hearth melting to the electron beam input power are 5065% and 6065% respectively. Overall heat transfer coefficient between molten metal and hearth cooling water is about 0.010.03 cal/cm2·s·K.
  • Equipment and Operation Results of 30t DC Arc Furnace at Topy Toyohashi Works

    pp. 520-527

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    With aim of reducing production costs, in January 1988, one of 30 t conventional AC furnaces at Toyohashi Works of Topy Industries, Ltd., was changed to a Direct Current (DC) arc furnace which was the first DC melter in Asia. It was jointly developed by M.A.N.GHH and BBC, and then designed and made by NKK.
    For reconstruction from AC to DC furnace, thyristor-controlled rectifier, DC reactor and bottom electrode were put additionally to 30 t arc furnace equipment. Electrode control equipment becomes simple, because only one electrode is used. The transformer and other furnace equipments were not changed.
    The DC arc furnace operation have brought us the following merits,
    1) The flicker of DC arc furnace was reduced to under 50%, compared with that of AC arc furnace.
    2) The problem of harmonics caused by the rectifier was solved by installing harmonic filters, which restrained harmonic component of the current under 5%.
    3) Any abnormal wear did not occur on the bottom and 330 heats of bottom electrode life was stably achieved in the intermittent operation.
    4) The decrease in melting cost of 900 yen/t was achieved, which was mainly due to a reduction in the consumption of graphite electrode, furnace refractory and so on.
  • Development of Gage Control System with Interstand Thickness Gage for Hot Strip Mill

    pp. 528-535

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    An interstand thickness gage was installed between the F4 and F5 stand of the hot strip finishing mill in Kashima Steel Works. It can measure the strip thickness with the same accuracy of the conventional thickness gage at the finishing mill exit, even if the pass-line of the strip is changed by the looper between F4 and F5 stand. Feedforward head-end gage control which adjusts the roll gaps of both F6 and F7 stand according to the F4 exit thickness deviation measured by the interstand thickness gage has been developed and is now in operation at the hot strip mill.
    The thickness accuracy at the head-end of the rolled strip can be improved over 30% by the feedforward head-end gage control compared with that by the conventional control.
  • Densification Mechanism Maps of Zn-22%Al Alloy Powder Based on Hot Pressing

    pp. 536-543

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    Densification behavior of Zn-22 mass%Al alloy powder having two different kinds of microstructures is studied by using Vacuum Hot Pressing(VHP). Sample-F is as-received powder which has fine (α+γ) microduplex structure and Sample-L, which has lamellar structure, is prepared by heating the Sample-F at 623 K for 3.6 ks followed by furnace cooling. VHP was preformed at 523 K under constant pressures from 2.5 to 100 MPa or constant cross-head speed between 0.1 to 10 min·min-1. Sample-F had a higher densification rate and a relatively higher density than Sample-L. From the VHP results, the densification maps of VHP for two samples were constructed by determing the relation between the VHP pressure and the densification rate. These maps indicated that the densification behaviors varied with microstructure of the powder. The map for Sample-F included a region having large m-value (m>0.3) while the map for Sample-L included no such a region. It was presumed that the densification process of Sample-F during VHP accelerated by superplastic VHP mechanism.
  • Temperature Dependence and Scattering of Toughness of A533 B Steels in Ductile-Brittle Transition Region

    pp. 544-551

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    Temperature dependence and scattering of the critical COD, δC, and J-integral values in the ductile-brittle transition region were investigated with A533 B steels the microstructures of which were widely varied. δC's at the maximum loads were in a linear relation with JY with a proportional constant of 0.49 irrespective to microstructures and test temperatures. It suggests that the stress strain field at the crack front area could be described with the Hutchinson, Rice-Rosengren solutions even at the D-B transition region.
    Linear relations also existed between δC as well as J and the stretch zone width, szw, but the data were grouped according to the relative locations of the test temperatures in the transition region. Analysis in terms of tearing modulus was also examined, suggesting that the resistance to the crack extension is temperature and microstructure dependent. It was discussed that the temperature dependence of the toughness and its scattering at a given test temperature could be discriminated in a sense that the former is related to the resistance of the crack extension while the latter is to the transition to the stable crack or brittle crack initiation.
  • Effect of Si Concentration on Secondary Recrystallization of Grain Oriented Electrical Steel Produced by Single Stage Cold Rolling Process

    pp. 552-557

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    A study has been made on the effect of the Si concentration on the secondary recrystallization of the grain oriented electrical steel produced by the single stage cold rolling process by use of MnS and AlN as inhibitors.
    (1) In case of the Si increase from 3.0 to 3.3 mass%, the secondary recrystallization temperature is shifted to higher under constant heating rate. In case of the Si increase to 3.7 mass%, no secondary recrystallization occurs.
    (2) The phenomena mensioned above are supposed to owe to the less intensity of (110) oriented primary grains and the larger primary grain size and the less effective inhibitors in case of the increased Si concentration.
  • Investigation of the Development of Cold-rolling and Annealing Textures in SUS304 Austenitic Stainless Steel

    pp. 558-565

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    The cold-rolling and annealing textures of SUS304 stainless steel strip has been investigated. The results obtained are as follows.
    1)The deformation texture of a strip rolled at room temperature can be described as a mixture of the ferritic type (α' martensite) and the brass type (retained austenite).
    2)The α' martensitic phase transforms reversely into austenitic phase at 700°C.
    The two components {111}<112>α' and {100}<011>α' can be related to the {110}<112> γ brass type texture by Kurdjumov-Sachs and Nishiyama relations, and the {112}<110>α' can be related to the {110}<001>γ.
    3)The recovery of internal stress accumlated by cold-rolling is faster in the {112} γ and {113} γ components than in the {110} γ component. The {110}<112> γ component of the deformation texture decreases for the annealing temperature above 800°C. The strong components of annealing texture above 900°C are consisted mainly of the near {112} <111> γ and near {113}<332> γ. These results suggest that the grains of the {112}{113} components recrystallize at lower temperature and absorb eventually yet unrecrystallized region of the {110} component.
    These structure changes during recrystallization process were confirmed by transmission electron microscopy.
  • Nondestructive Evaluation of Temper Embrittlement of Cr-Mo-V Cast Steels by Electrochemical Method Using Calcium Nitrate Solution

    pp. 566-573

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    Quantitative evaluation of temper embrittlement of turbine casing material, Cr-Mo-V cast steel, by means of anodic polarization behavior in calcium nitrate solution was investigated. Furthermore, based upon these results, nondestructive electrochemical method for detection and evaluation of temper embrittlement of Cr-Mo-V cast steel is newly developed with high sensitivity. Intergranular Corrosion (IGC) occurs only on temper embrittled samples during anodic polarization process in calcium nitrate solution. In polarization curves measured at 60°C, the characteristic changes such as increases in current density at passive potential range and in passivation potential attributable to IGC have a excellent correlation with shifts in FATT caused by temper embrittlement. On the other hand, in polarization curves measured at 30°C, increases in the current density of the second peak current attributable to IGC have a good correlation with shifts in FATT. By use of these electrochemical characteristic values, the degree of temper embrittlement can be quantitatively estimated.
  • Development of a New Ni-base Superalloy for Industrial Gas Turbine Combustor by Statistical Alloy Design Method

    pp. 574-581

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    A new Ni-base superalloy has been developed for gas turbine combustor. In the first stage, multiple regression analysis was conducted on the published material data of superalloys. The eatimation equations were established to estimate the mechanical properties such as stress rupture strength and tensile properties, and physical properties such as density and thermal conductivity. Alloy design program by statistical method was made to select the alloy chemical compositions which will satisty the requirements of structural design. By means of this alloy design method, 22%Cr-8%Co-9%Mo-3%W-1%Al-0.3%Ti-Ni base alloy ( %: mass%) was set up for combustor superalloy. The superalloy plates using these alloy elements were manufactured by vacuum induction and remelting process weighing 2 000 kg.
    The mechanical and physical properties were examined on those plates, and it is confirmed that these estimated values by alloy design coincide with the testing measured values. As above test results, it is considered that the statistical alloy design is useful for developing new superalloys. The new Ni-base superalloy also has good workability, good mechanical and physical properties for industrial gas turbine combustor.
  • Effects of Nitrogen Content and Tempering Treatment on Creep Rupture Properties of 9Cr-1Mo-V-Nb Steel with Simulated HAZ Heating

    pp. 582-589

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    Creep rupture properties of 9Cr-1Mo-V-Nb steel welded joints change with chemical compositions and heat treatments. Therefore, simulated HAZ heating below or over Ac1 temperature of 830°C was conducted in order to investigate microstructural changes of welded joints of the steel. Effects of nitrogen contents and tempering treatments on hardness and creep rupture properties were discussed. The results are summarized as follows.
    (1) Hardness and creep rupture strength of the steel heated at 850°C ( simulated HAZ heating) decreased significantly after post-weld heating at 740°C for 5 h. It was confirmed that recovery and softening of martensitic structure were accelerated by partially γ-transformed heating just over Ac1 temperature.
    (2) On the above simulated HAZ heating, finely dispersed Vanadium Nitride (VN), which increased in amount by addition of nitrogen, was observed. These precipitates were confirmed to retard recovery, and to improve creep rupture strength effectively.
    (3) In case of relatively low temperature tempering at 620°C, excess free carbon and nitrogen precipitated as fine VN and M23C6 during simulated HAZ heating and post-weld heat treatment. These precipitates were confirmed to improve creep rupture strength.
  • State Analysis for Cr-rich (bcc) Phase and Carbides in High Chromium Nickel Base Austenitic Alloys

    pp. 590-597

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    A method of state analysis for α' phase and carbides in high chromium nickel base austenitic alloy has been established. And then, precipitation behavior of the α' phase and carbides and the effect of α' phase on the property of this alloy were investigated by using this method.
    The results obtained are summarized as follows.
    (1) The α' phase and carbides are quantitatively extracted by potentiostatic electrolysis in 10%HCl-methanol electrolyte.
    (2) Only the α' phase in the above mentioned precipitates is dissolved by (1+5)HCl dissolution treatment. Consequently, the amount and composition of the α' phase and carbides can be determined by analysis of this solution and the residues of this treatment, respectively.
    (3) The α' phase was bcc chromium phase replaced by a small amount of Mo, Fe and Ni.
    (4) In the case of alloys aged for 3 000 h at various temperature, the precipitation of the α' phase was found at aging temperature from 923 K to 1 073 K.
    (5) The creep rupture strength was improved by the uniform precipitation of intragranular α' phase.
  • Determination of Rare-earth Elements in Metallic La, Pr, Nd, Gd and Tb by Glow Discharge Mass Spectrometry

    pp. 598-604

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    Trace analysis of rare-earth elements (REEs) in metallic REE matrices (La, Pr, Nd, Gd and Tb) by the glow discharge mass spectrometry was investigated. Optimum operational parameters of the glow discharge which affected directly ion beam intensity were examined. Preburning was performed to remove surface contamination before analysis. Preburn time was about 10 min under discharge conditions. Spectral interferences due to polyatomic species such as oxide, hydride and argide were examined. Then, alternative isotopes are used for analysis except for monoisotopic elements. Low ppba detection limits were obtained. The relative standard deviations of five repetitive measurements were 0.8%5.0% for 100 ppm level and 40% for less than 1 ppm.

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