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

Tetsu-to-Hagané Vol. 58 (1972), No. 7

  • Reduction of Fine Iron Ores in Gas Conveyed Systems

    pp. 821-829

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    High reaction rate of finely powdered iron ores was expected because of their large reaction surface. In order to take advantage of this property, gas conveyed system was applied to the reduction of finely powdered iron ores, and feasibility of the process was studied. Hydrogen reduction of very fine powder of pyrite cinder, which had been very difficult by fluidized bed, proceded successfully in this way, and the capacity of processing seemed to be larger than that of fluidized bed process for similar effective volume. Hydrogen reduction of fine iron ores by the gas conveyed system was largely affected by water vapor formed during the reduction process. Reduction of fine hematite are by very dilute phase was studied and relations between the rate constant and the vapor pressure were determined. From these relations, a rate equation for high solid/gas ratio was derived. It was shown that this equation was valid for relatively concentrated solid gas systems.
  • The Effect of Chemical Reactions on the Interfacial Tension between Molten Iron and CaO-SiO2-Al2O3 Slag

    pp. 830-841

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    The interfacial tension measurements were made for liquid slag-liquid metal interfaces with the sessile drop method. A radiographic technique was used to determine the profile of an aluminum-, or sulfur-containing iron drop which was placed on an alumina substrate and covered by a layerof CaO-SiO2-Al2O3 slag in an alumina or a graphite crucible.
    An anomalous decrease in the interfacial tension was observed for iron melts containing more than 2% aluminum. This decrease, which resulted in the interfacial tension of less than 100 dyne/cm, was proved to be due to brisk reduction of silica by aluminum. For sulfur-containing iron saturated with carbon, desulfurizing took place, and the interfacial tension was considerably decreased to less than 500 dyne/cm only when the rate of sulfur transfer exceeded 3-10-6 mol/min/cm2. Whenever this criterion was exceeded, marked disturbance resulting in a serrated interface was observed at the slag-metal boundary.
  • The Effect of Strain Rate, Temperature, Grain Size and Si Content on the Lower Yield Stress and Flow Stress of Fe-Si Alloys

    pp. 842-858

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    The lower yield stress and flow stress of two kinds of Fe-Si alloys with various grain sizes were measured in the temperature range between 77 and 473°K with strain rates varying from 10-6 sec-1 to 33 sec-1. These data were analyzed using the Hall-Petch relation,
    It was found that the addition of Si to iron increased the athermal component of friction stress and decreased the thermal component. This decrease in the thermal component of friction stress caused the solid solution softening phenomena in Fe-Si alloys at low temperatures. The relations between the activation volume or activation energy of both alloys and the effective shear stress were not affected by the amount of Si added, but whole relationship was different from that of the pure iron.
    The differences in the low temperature deformation characteristics between iron and Fe-Si alloys were explained from the viewpoint of interaction between moving dislocation and elastic stress field in the lattice around the solute atom, Si.
    The strain rate dependences of the lowere yield stress of Fe-Si alloys varied continuously in the range of strain rates from 10-6 sec-1 to 33 sec-1. The relation between the effective component of lower yield stress and strain rate was well approximated by a power function at all temperatures tested.
  • Improvement on Age Hardening Properties and Creep Rupture Strength of P-Containing Austenitic Heat Resisting Steel due to Various Cooling Procedures

    pp. 859-871

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    he effect of cooling rate from solution temperature on the age hardening properties of a P-containing austenitic heat resisting steel was investigated.
    Little difference in the age hardening properties was detected between a water-quenched specimen and a air-cooled one, while at a slower cooling rate as in furnace cooling, the aged hardness was lower than that of a water-quenched or a air-cooled specimen.
    Transmission electron microscopic examination revealed that in specimens aged afer water quenching or air cooling very fine precipitates were formed in uniform dispersion almost independently of dislocation of which density would vary with cooling rate. The cause of this very fine and uniform dispersion of precipitates will probably be attributed to P contained in this steel. It will be also assumed that this independence of nucleation on dislocation leads to the quench insensitivity of this steel. On the toher hand, it was detected that in a furnace-cooled specimen precipitates were already nucleated during cooling from solution temperature, and these pre-formed precipitates affected appreciably the dispersion of precipitates formed at subsequent aging.
    On the basis of above results, two step cooling process from solution temperature was investigated in order to obtain high aged hardness as well as marked grain boundary serration. It involved following processes:(1) furnace cooling through a higher temperature region where grain boundary serration due to coarse precipitates occurred markedly but precipitates were not yet nucleated in the matrix, and (2) subsequent air cooling. This two step cooling process resulted in a marked age hardenability of the steel during aging.
    It was found that the creep rupture sterngth of this steel was improved significantly by the above heat treatment; e. g. 1000hr rupture strength reached to 28-29 Kg/mm2 at 700°C.
  • Precipitation of A1N in Cold-worked High Purity Fe-Al-N Alloy

    pp. 872-884

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    The precipitation process of A1N in a cold worked high purity Fe-0.09A1-0.01N alloy was studied. The alloy was made from a zone refined high purity iron bar (>99.99%) and an Al-Fe alloy by embedding the latter at an interval along the specimen axis and zone refining the composite in a N2-H2 atmosphere. The alloy was subsequently quenched into ice water after solution treatment of 1 250°×1hr and cold drawn 68.6% at room temperature. The electrical resistivities of the wires, annealed isochronally and isothermally, were measured in liquid nitrogen, and the precipitates of A1N were examined by electron microscope extraction replica method. The results obtained were as follows;
    1) A large decrease of the electrical resistivity was observed at the temperature range from 450°C to 620°C which was attributed to the precipitation of A1N. This temperature range was lower by about 100°C than that in the not-strained specimens.
    2) The precipitation processes under about 580°C could be described as a first order reaction after a respective certain period of time, for which the activation energy of reaction was 58 Kcal/mol, which suggested that the precipitation of A1N in the cold worked matrix was controlled by the diffusion of Al in cc-iron.
    3) The cubic lattice structure of A1N was occasionally observed in the early stage of precipitation, but most of the precipitates observed in the high purity specimens used here were identified to be A1N of the hexagonal lattice structure.
  • Study of Brittle Fracture Surface in Relation to Microstructure of High Carbon Steel

    pp. 885-898

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    The brittle fracture surfaces of the isothermally transformed high carbon steel (0.7%C) were investigated. The various microstructures which were lamellar pearlite, degenerate pearlite, upper bainite, lowere bainite, and martensite were obtained based on the TTT diagram.
    The brittle fracture surfaces were prepared by Charpy impact test at-196°C The direct correspondences between the brittle fracture surfaces and the microstructures were carried out in scanning electron microscope.
    The mode of quasi-cleavage surfaces was closely related to the decomposition of austenite to ferrite. The crystallographic orientation of the cleavage plane was determined as {100} by means of facet pit technique and goniomicroscope. The fracture facets of pearlite, degenerate pearlite, upper bainite and lower bainite corresponded to the domains in which the crystallographic orientation difference in respect to the cleavage surface {100} were small.
    Such the domains on the other hand, were not seen in the case of martensite. It seemed that the martensite plates itself formed the fracture facet. From this point of view, there was a great difference in fractographic appearance between high carbon martensite and low carbon lath martensite. It is probably due to the difference of the crystallographic behaviors in transformation.
  • Determination of Phases in Tool Steels Quenched from Liquid State

    pp. 899-920

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    Extensive studies are being carried out with high speed steel made from atomized powders, mainly for the establishment of mass production technique and the investigation of various properties of such steels. Almost no literature has been published on the metallographic study of the steels rapidly quenched from liquid state. Therefore, the solidification process during quenching of tool steels from liquid state was studied in this work.
    Microscopic observation, X-ray diffraction and electron probe microanalysis were performed on the atomized powders, thin plates by splat cooling, and beads made by several methods such as electron beam and transfer-plasma melting. The materials studied included high speed steels, cold work die steels and hot work die steels.
    The results are summarized as follows.
    (1) When high speed steels and die steels were quenched from liquid state, carbides were crystallized in the form of extremely fine particle or plate.
    (2) Quenched from liquid state, high speed steels were crystallized in the following steps.
    Primary γ, γ+cabide eutectic
    (3) Hot work die steel was crystallized in the same process as high speed steels but no β-ferrite was found.
    (4) Carbides crystallized in SKH9, SKH54 high speed steels and SKD61 hot work die steels were not M6C+MC type but M2C+MC type.
  • On the Heat-Treatment Characteristics of Containing Silicon-Nickel-Chromium-Molybdenum Carburizing Steel

    pp. 921-931

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    High silicon carburizing steels were developed and tested in order to increase the pitting resistance and the fatigue life of heavy duty gears.
    The results are summarized as follows;
    (1) Effects of silicon on the amount of retained austenite and on M, point of the carburized layer were not found by X-ray and dilatometric methods.
    (2) Surface carbon content and carburized depth of these steels decreased with increasing silicon content. But the hardenability increased with silicon addition.
    (3) Surface hardness, rolling fatigue life and toughness of these carburized steels were improved by silicon addition.
    (4) Rapid heating and quenching after carburizing gave better qualities to those steels compared with slow heating and quenching.
  • Metal-Slag Reactions (Equilibrium and Kinetics)

    pp. 932-954

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  • On Attending Japanese Iron-Steel Mission to Nordic Countries

    pp. 955-959

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  • Steels for Construction Machinery

    pp. 960-967

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  • 抄録

    pp. 968-973

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