ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 30 (1990), No. 5

  • A Method of Observing Fine Precipitates in Alloys with a Field-ion Microscope

    pp. 341-346

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    DOI:10.2355/isijinternational.30.341

    A method of observing a few atom-layer thick precipitates in alloys with FIM is described. On the spherical crystal surface of an FIM specimen, many atomic planes are exposed. On the low-index planes, the topmost surface layer is nearly circular and has a relatively large diameter of 5 to 10 nm. It is pointed out that when a thin precipitate plate intersects the middle of the top layer, a clear field-ion image of the precipitate atoms can be obtained without a disturbance by the image of matrix atoms. From the images of a copper monolayer in aluminum and of a nitride plate in iron, the image formation mechanism on the low-index surfaces are discussed.
  • Analysis of Rate of Hydrogen Reduction of Porous Wustite Pellets Basing on Zone-reaction Models

    pp. 347-355

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    DOI:10.2355/isijinternational.30.347

    Porous wustite pellets were reduced with hydrogen at 900°C, and reduction curves, position of reaction zone and local fractional-reduction profiles were measured.
    Basic equations for the grain model were re-examined and solved as they were (unsteady numerical solution), and under quasi-steady (quasi-steady numerical one) and moreover linearization approximations (quasi-steady analytical one). When rate parameter values are selected suitably in each case, measured reduction curves and reaction zone behavior are comparatively well reproduced by the calculated results. Thiele's modulus is about 10-14 under the present experimental conditions and reaction fashion differs much from the one for unreacted-core shrinking model.
    When the unsteady numerical solution is calculated, reducible oxygen density is divided by M to reduce the computation time; the error at M≤2000 is within a permissible range, although the solution most faithful to the basic equations is obtained at M=1. Comparison between the unsteady and the quasi-steady numerical solutions shows that the latter is an approximate solution having rather good accuracy. The quasi-steady analytical solution is better than the others from practical viewpoint, because its computation time is the shortest and degree of agreement between the measured and the calculated results is much the same among the three.
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  • A Model Study of Residence Time of Metal Droplets in the Slag in BOF Steelmaking

    pp. 356-361

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    DOI:10.2355/isijinternational.30.356

    Residence time of metal droplets generated by an oxygen jet impinging on molten bath surface in the slag was investigated in a 3-D two phase (mercury/glycerine) model. The residence time (τ =Q2/q1) was obtained from measurements of the amount of emulsified mercury in glycerine at steady state (Q2) and the drop generation rate (q1). It has been found that the mean residence time increases with increasing top gas flow rate and decreases with increasing bottom gas flow rate. Also, it increases at first and then decreases with increasing lance height. Maximum mean residence time was achieved at a certain lance height.
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  • Simultaneous Injection of Pulverized Coal and Dolomite into Blast Furnace Tuyeres

    pp. 362-371

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    DOI:10.2355/isijinternational.30.362

    For the simultaneous control of Si and S contents in pig iron, a simultaneous injection of pulverized coal and flux (dolomite in this research) into blast furnace tuyeres was proposed. Fundamental researches were performed on slag formation property, SiO gas generation reaction and transport properties of pulverized coal-dolomite mixture to investigate merits and presumed problems of simultaneous injection of pulverized coal and dolomite. The significant improvement of slag formation property and the suppression of SiO gas generation reaction were confirmed. Pressure drops in both horizontal and vertical transport pipelines were experimentally evaluated. Distribution characteristics to tuyeres and abrasion of transport pipeline of pulverized coal and dolomite mixture were found to be no problem for commercial application. Based on the fundamental researches, a commercial test operation with simultaneous injection of pulverized coal of 20 kg/THM and dolomite of up to 15 kg/THM were performed at Kokura No. 2 blast furnace, Sumitomo Metal Industries, Ltd., for 2 weeks. Si and S contents in pig iron were decreased through dolomite injection of 15 kg/THM by 0.06 and 0.005%, respectively. The increase of corrected coke rate of 6.2 kg/THM was obtained by dolomite injection of 15 kg/THM. No harmful change of inner furnace state was observed and the stable furnace operation can be expected with simultaneous injection of pulverized coal and dolomite.
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    Readers Who Read This Article Also Read

    1. Mechanisms of Hanging Caused by Dust in a Shaft Furnace ISIJ International Vol.31(1991), No.9
    2. Prediction of a Blast Furnace Burden Distribution Variable ISIJ International Vol.36(1996), No.9
    3. Suppression of the Formation of Large Pores in the Assimilated Parts of Sinter Produced Using Pisolitic Ores ISIJ International Vol.36(1996), No.11
  • Mathematical Representation of the Velocity, Temperature and Solid Fraction in an Electromagnetically Stirred Solidifying Melt

    pp. 372-380

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    DOI:10.2355/isijinternational.30.372

    A mathematical model has been developed to describe the velocity, temperature and solid fraction in an electromagnetically stirred Al-5%Cu alloy in which 15% B4C particles were initially suspended. In the model, we allowed for the rheology of the melt-solid slurry and the release of latent heat either at the melt-solid interface, in the bulk or at an intermediate stage between those extremes. The calculations have shown that the evolution of the temperature and solid fraction profiles were not significantly affected, either by the stirring rate or by the choice of the location of release of latent heat.
  • An Assessment of the Heat and Fluid Flow Phenomena Inside Plasma Torches in Non-transferred Arc Systems

    pp. 381-389

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    DOI:10.2355/isijinternational.30.381

    A mathematical representation has been proposed to represent the behavior of non-transferred arc plasma plumes without the need to specify the temperature and velocity of the plasma gas upon exiting the torch. The need to make this assumption has been the principal drawback of plasma modeling efforts to date. In the present work we postulate an idealized shape for the plasma column within the torch, with a constant heat generation rate per unit volume and then solve the coupled heat flow and fluid flow equations both within and outside the torch. The computed results, in the generation of which allowance has been made for heat exchange between the plasma and the torch walls, were very interesting, in that they showed that the temperatures and velocities found for the plasma plume were relatively insensitive to the dimensions postulated for the plasma column. Indeed, for the particular conditions examined a nearly 17-fold change in the volume of the arc column produced only a 13.5% difference in the maximum exit temperature from the torch. It follows that by making "reasonable assumptions" for the dimensions of the arc column one may provide fairly good predictions for the temperature and velocity profiles in the plasma plume; in fact the predictions based on this model were found to be in very good agreement with experimental measurements. Another potentially interesting finding was that any initially imposed swirl on the plasma gas was overwhelmed by the thermal expansion of the plasma within the torch; in fact very special arrangements would be needed in order to produce a strong swirl in the exit gas.
  • The Effects of Grain Boundary Phosphorus Segregation and Heat Treatment on Toughness of 9% Ni Steel and its Welded Joint

    pp. 390-396

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    DOI:10.2355/isijinternational.30.390

    Effects of phosphorus (P) and heat treatment on toughness have been investigated on a quenched and tempered 9% Ni steel base metal and its welded joint simulated by a thermal cycle simulator. The mechanism of toughness improvement by the diminution of P component was examined by mechanical tests, microstructure observation and computer simulation of the grain boundary segregation. The critical CTOD value and Charpy absorbed energy in the base metal showed remarkable deterioration as increasing P content, when the cooling rate after tempering was lower than 1×10-2 K/s. Simulated bonds showed reduction of toughness when the P level was higher than 0.008% and/or the cooling rate after post weld heat treatment (PWHT) was lower than 1×10-2 K/s. The Charpy absorbed energy of base metal was higher than that of PWHT welded joint when they showed the same critical CTOD value. Intergranular ductile fracture was occurred in the base metal, while intergranular brittle fracture in PWHT welded joint was observed.
    The effect of cooling rate following the tempering on the grain boundary segregation of P was estimated by computer simulation, based on Guttmann-McLean theory. The computed amount of P segregation in grain boundary was closely related to the toughness both for a base metal and a simulated bond. It was also suggested that when the grain boundary segregation of P was lower than 0.1, high toughness level was obtained in the base metal and the simulated bond. The difference of toughness between the base metal and the simulated bond was attributed to the coarsening of grain size by the welding thermal cycle. The 9% Ni steel with P level lower than 0.005% shows excellent toughness in the base metal and the welded joint.
  • Corrosion Behaviour of the Fe-Cr-V-Ru System in Reducing Acid Solution

    pp. 397-402

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    DOI:10.2355/isijinternational.30.397

    The corrosion behaviours of Fe-24Cr-6V alloys containing 0.12, 0.24, and 0.35wt% Ru additions in non-oxidizing acid solutions were studied by means of the electrochemical and Auger electron spectroscopic techniques. The weight-loss measurements show that the addition of Ru to the Fe-24Cr-6V alloy in the composition range 0.12 to 0.35% is very effective in increasing the corrosion resistance of this alloy in a 5% H2SO4 acid solution at 70 and 98°C, respectively. Also, the addition of Ru to the Fe-24Cr-6V alloy is found to be beneficial in the concentration range 0.24 to 0.35% range when the alloy is exposed to 5% HCl solution at 70 and 98°C, respectively. AES results reveal that the spontaneously passivated films formed on the Fe-24Cr-6V-Ru alloy system in 5% HCl solution at 25°C are enriched in chromium and vanadium but depleted in ruthenium.
  • Brazing of Alumina to Copper Using Cu-Ti-Co

    pp. 403-408

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    DOI:10.2355/isijinternational.30.403

    Joint of alumina ceramics (98.1% Al2O3) to copper was made using Cu-(10-50wt%)Ti-(5wt%)Co brazing filler metals. The Cu-30wt%Ti-5wt%Co brazing achieved the highest shear strength 195 MPa at room temperature.
    The composition and structure of the ceramic-metal bond zone in the Al2O3-Cu joints were analyzed by SEM, EPMA and X-ray diffraction.
    The microstructure of interface between Al2O3 and Cu-Ti-Co brazing filler metal was shown to form the reaction layer consisting of (Al, Ti)2O3 solid solution oxide, titanium oxide TiOx and CoAl2O4 compound.

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