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

ISIJ International Vol. 30 (1990), No. 6

  • Factual Databases for Materials Design and Manufacturing

    pp. 409-416

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    DOI:10.2355/isijinternational.30.409

    The present status of scientific and technological factual databases is reviewed. The number of source information which should be entered into a materials database is very large, therefore the databases must be optimally structured in records and files. As an example, the structure of JICST TH (the Japan Information Center of Science and Technology Thermophysical and Thermochemical Property Database) is presented. Discussion is made on characteristics of data items, validation of materials databases, the present status and future aspect of delivery and database systems.
  • Influence of Original Structure on the Kinetics and Mechanisms of Carbon Monoxide Reduction of Hematite Compacts

    pp. 417-425

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    DOI:10.2355/isijinternational.30.417

    Green, porous and dense Fe2O3 compacts having 54, 35 and 8% porosity respectively were obtained at different temperatures. The structure of these compacts was examined and correlated to their thermal history. These compacts were isothermally reduced with carbon monoxide at 500-1100°C using weight-loss technique. The structural changes accompanying the reduction process were examined with mercury pressure porosimeter and with optical and scanning electron microscopes while the different phases formed during reduction was identified by X-ray diffraction technique. At the initial stages of reduction, the rate was increased with temperature and with increase in original porosity of compacts. With progress of reduction, a reduction rate minimum was observed at 950-975°C and was attributed to sintering and densification of γ-iron. The retardation in the rate was not detected during the reduction of dense compacts due to the disintegration of iron grains resulting from carbon deposition and subsequent reactions. The values of apparent activation energy were calculated and correlated with both the original structure of compacts and the reduction mechanisms.
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  • Partition of Manganese between α-Fe2O3 Crystal and Na2O-B2O3 Melts

    pp. 426-434

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    DOI:10.2355/isijinternational.30.426

    A study has been made of the partition of Mn between α-Fe2O3 crystal and sodium borate fluxes at the temperatures ranging from 800 to 1100°C as a function of flux compositions.
    The total Mn content in α-Fe2O3 is linearly related to that in flux in the studied concentration range. The temperature dependence of the partition coefficient kT, Mn=(wt%Mn)solid/(wt%Mn)liquid was found to be positive. It was found that Mn is present as Mn3+ in α-Fe2O3 crystal and Fe and Mn in flux are present as Fe3+ and Mn2+, respectively. On the basis of the mutual interaction of the Mn3+/Mn2+ and Fe3+/Fe2+ redox pairs: Fe3+(s)+Mn2+(l)=Mn3+(s)+Fe2+(l), the partition between solid and liquid phases with a different valency state has been discussed.
  • Characterization of the Formation, Propagation, and Recovery of Sticker/Hanger Type Breakouts

    pp. 435-443

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    DOI:10.2355/isijinternational.30.435

    A non-standard, horizontal water passage mold has been used to investigate the initiation, propagation, and recovery of sticker and hanger type breakouts. The velocity of propagation of the hot spot in the shell down the mold has been measured to be 0.5 times the casting speed. The causes for sticker breakouts have been identified as casting too fast, changing cast speed or liquid level too rapidly, and/or insufficient lubrication between the mold and solidifying shell. Sticker or hanger breakouts have been shown to initiate virtually at the meniscus in all cases. The variation in instantaneous mold heat transfer rate and mold wall temperature profiles have been shown to be effective to predict sticker or hanger breakouts; the time variation of both mold friction and overall mold heat transfer rate has been shown to be ineffective in detecting sticker or hanger breakouts. The experimental observations have led to a theoretical hypothesis for the mechanism of initiation of the sticker and propagation of the hot spot in the sticker breakout. The events occurring during and after the initiation of sticker type breakouts followed by their recovery before spillage of liquid steel have also been characterized.
  • Grain Boundary Segregation Behaviour of Phosphorus and Carbon under Equilibrium and Non-equilibrium Conditions in Austenitic Region of Steels

    pp. 444-450

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    DOI:10.2355/isijinternational.30.444

    Auger electron microscopic analyses were performed to clarify grain boundary segregation behaviour of phosphorus and carbon in the austenitic region of steel. Grain boundary migration during recrystallization and grain growth of austenite gave rise to non-equilibrium segregation which resulted in a higher solute concentration on grain boundaries than that of equilibrium segregation. The increment of segregation caused by migration depended on the boundary velocity. In recrystallization, faster diffusing elements such as carbon, segregated with higher concentrations. It was suggested that the solute sweep effect during grain boundary migration caused the non-equilibrium segregation.
  • Evaluation of Creep Damage in Some Major Components of Power Generator

    pp. 451-456

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    DOI:10.2355/isijinternational.30.451

    Life extension of installed machinery and equipment has become a matter of strategic importance with significant economic implications especially in power plants.
    The paper presents a complex of methods aimed at assessment of the residual service lives of major components of power plant machinery (steam turbines, steam line systems) under creep conditions. The methods are based on a mathematical model of properties of creep-resistant steels based on the dislocation mechanism for which stochastic behaviour of material in the course of the strain mechanism has been assumed. A method is proposed to evaluate the equivalent service load in actual service conditions by means of a computerized data acquisition. The method is applied to monitor creep damage of steam turbine pipelines. Creep damage of turbine rotors and casings and plastic deformation in their critical points were estimated numerically.
    The actual time span of reliable operation of a component is assessed by these method and compared with results obtained by diagnostic methods prepared in cooperation with manufactures of power generating machinery.
  • Effect of Carbon, Phosphorus and Nitrogen Contents in Steel on Machined Surface and Cutting Force

    pp. 457-463

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    DOI:10.2355/isijinternational.30.457

    The effect of carbon, phosphorus and nitrogen content on the surface roughness and cutting force was studied with regard to the microstructure of specimen and the behavior of void formation and built-up edge during cutting. Specimens to plunge-cutting were prepared by adding each element into pure iron.
    Two-phase microstructure such as ferrite-pearlite and ferrite-grain boundary where phosphides precipitate, increase the surface roughness and reduce the cutting force. On the contrary, the single-phase microstructure, that is to say, ferrite containing soluble nitrogen, slightly improves the surface roughness but raises the cutting force.
    Since the ductility of each phase in the two-phase microstructure is different from each other, the formation of voids takes place along the interface due to cutting force. The void formation behavior in the primary shear zone is closely related to the projection length of the built-up edge and the surface roughness.
  • Morphology and Microstructure of Pulse Electrodeposited Zinc-Iron Binary Alloys

    pp. 464-468

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    DOI:10.2355/isijinternational.30.464

    Zinc-iron electrodeposited sheet steels have been widely adopted for automobile bodies for their improvements in the corrosion resistance and paintability. In principles, these properties depend on the crystal structure, morphology and microstructure of deposits. The deposits with various pulse current-off time have been electrodeposited from sulfate bath and examined by scanning microscopy and X-ray diffraction. All the deposits consist of the η- and Γ-phases, and the deposit morphology consists of hexagonal columnar crystals and Γ-phase granular crystals. These hexagonal columnar crystals consist of the η-phase plates and fine granular Γ-phase dispersively precipitate within the grain and grain boundary of these η-phase plates.
    For the 1.0 ms pulse current-off time deposit, the granular crystals form only on the (00·1)η of hexagonal columnar crystals. For the deposit more than 1.0 ms, these granular crystals form both on the (00·1)η and {10·0}η of hexagonal columnar crystals. The amount of granular crystals increases as the increase of off time. Also the deposit cross-sectional observation reveals the increase of white microstructures whose zinc contents are less than dark microstructures. The X-ray diffraction shows the decrease of diffraction itensity and number of diffraction lines of η-phase, and the increase of those of Γ-phase.
  • Numerical Effects of Gas Mass Flow Rate on Flow Properties in Supersonic Nozzle Flows of Two-phase Mixtures

    pp. 469-471

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    DOI:10.2355/isijinternational.30.469

  • Stability of Interstitial Elements in Metal Lattice Evaluated by Statistical Thermodynamics

    pp. 472-474

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    DOI:10.2355/isijinternational.30.472

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