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

Tetsu-to-Hagané Vol. 59 (1973), No. 7

  • 研究管理雑感

    pp. 861-862

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  • Decarburization of Molten High Chromium Steel under Reduced Pressure

    pp. 863-873

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    Decarburization of molten Fe-C-Cr steels by oxygen top blowing under reduced pressure has been studied in a 100kg capacity vacuum induction furnace. The results are summarized as follows:
    (1) Decarburization process could be devided into three stages; the first stage in which decarburization reaction proceeds by the preferential oxidation of carbon, the second stage in which carbon and chromium in the bath are oxidized simultaneously, and the third stage in which the reaction proceeds by the preferential oxidation of chromium. The relationship between carbon and chromium in the last stage was approximated by the following equation.
    log ([%Cr]/[%C])=-12500/T+9.04
    (2) The oxygen efficiency for the decarburization reaction in the first stage was found between 74% and 78% for the Fe-C heats and between 37% and 64% for the Fe-C-Cr heats. The efficiency for the Fe-C heats was hardly effected by the bath temperature and blowing condition, but that for the Fe-C-Cr heats increased with increasing in bath temperature and in the size of oxygen lance diameter and with decreasing in oxygen flow rate.
    (3) Experimental data concerning oxygen balance and activation energy suggested that the decarburization reaction resulted from the reduction of iron and chromium oxides which were formed by oxygen jet at the surface of molten metal cavity. It could be stated that the rate of decarburization was affected not only by the oxygen flow rate but also by physical and chemical properties of oxide and metal splashing behavior resulted from CO boiling.
  • Formation of CO and Macrosegregation during Uni-directional Solidification of Iron

    pp. 874-886

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    Experimental studies have been made of the uni-directional solidification of iron with a view of studying the mechanism of solidification with the formation of CO. From the experiments at the solidification velocity of 5mm/min and [%C] L≈0.1, it is shown that oxygen contents of 0.003 to 0.006% correspond to the transitional concentrations for the formation of CO bubbles and macrosegregation. In this concentration range elongated blowholes are formed, resulting in lowering kc* and kp*. At oxygen contents higher than 0.006%, kp* is unaffected by the increase of oxygen concentration of the melt, whereas kc* tends to decrease at high oxygen contents.
    An expression has been derived to predict the onset of constitutional supercooling for the case of solidification without the formation of CO. From the calculation, it is suggested that the solidification morphology at oxygen contents below 0.003% is dendritic structure.
    The solute distribution at solid-liquid fronts growing with bubble formation is explained on the bases of the model that the enriched liquid is being pushed to the liquid ahead of the growth front. Due to the consumption of carbon in the reaction with oxygen kc* is lowered more than kp*.
    It is shown that the present data give a satisfactory explanation to the phenomena occurring during solidification of a rimming steel.
  • Effect of Solidification Velocities on the Formation of CO Blowholes during Uni-directional Solidification of Iron

    pp. 887-897

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    The present paper deals with the experimental study made of the uni-directional solidification of iron with blowhole formation at various solidification velocities ranging from 5 to 13.5mm/min and [%C]L≈0.1. It is found that the lower limit of the transitional oxygen concentration, [%0]t, 1, for the formation of elongated blowholes is 0.003-0.004% and almost independent of solidification velocity ƒ. On the other hand, the upper limit of the transitional concentration, [%O]t, u, increases with increasing ƒ until ƒ=10mm/min is reached, beyond which [%O]t, u tends to decrease.
    On the bases of the equilibrium solidification model, an attempt has been made to calculate the lower limit of the transitional oxygen concentration. The calculation is in good agreement with the experimental findings.
    The relationship found between the upper limit of the transitional concentration and solidification velocity is interpreted in terms of the relative rates of growth of the bubble and of advance of the interface.
    A series of experiments has been made of solidification from the iron melt in equilibrium with CO-CO2 gas mixtures. It is shown that both kp* and kc* increase with the increase of solidification velocity.
  • On the Relation between the Shape of a Wire Drawing Die and Its Abrasion

    pp. 898-906

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    From the viewpoint that the shape of a wire drawing die has some influence on its abrasion, a research was made to examine the relation between drawing force and the die shape by using two kinds of tungsten carbide dies whose shapes are different and a diamond die. The factors that cause the difference in abrasion of the dies were investigated. The results obtained are as follows:
    1) The mean value and the fluctuation of drawing force in the case of tungsten carbide die increase with increasing the length of bearing portion, and the abrasion of the die with longer bearing portion is much larger than that of shorter bearing. The abrasion of the die is represented by the increase in diameter of drawn wire.
    2) The ratio of length of bearing portion to diameter of the tungsten carbide die is an index of magnitude of the drawing force, but this value can not be applied to the comparison of the drawing force for tungsten carbide die and that for the diamond die. It is considered that this is due to different surface conditions of both dies.
  • Effect of Nitrogen, Boron and Phosphorous on High Temperature Strength of 18Cr-10Ni and 18Cr-10Ni·Mo Austenitic Steels Bearing Small Amounts of Titanium and Niobium

    pp. 907-918

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    It has been previously reported by one of the authors that with the combined addition of small amounts of Ti and Nb the creep rupture strength of 18Cr-8Ni austenitic steel is markedly increased. In this work, the effects of further addition of N, B, and P on the creep rupture properties of 18-10 and 18-10. Mo steels both bearing small amounts of Ti and Nb have been studied.
    It has been found that the combined addition of 0.1%N and 0.02%B to these steels is effective for increasing the rupture strength, and the addition of 0.3%P to 18-10·Ti·Nb·Mo steel is more effective, giving a high 700°C-104hr rupture strength of 17kg/mm2. The cause of the strengthening effects of these elements have been discussed with relation to changes in distribution of carbide M23C6 precipitated within austenitic grains, and it has been attributed to a decrease in the misfit between matrix and the carbide M23C6, resulting in retardation of the carbide coalescence. Especially, electron microstructures of replicas extracted from 18-10 and 18-10·Mo steels bearing 0.3%P look like homogeneous precipitations of the carbide M23C6, and these fine carbide distributions have been considered to be the main cause of the strengthening action of P.
  • On the Pearlite Reaction in a Hadfield Steel

    pp. 919-928

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    The precipitation of proeutectoid carbide and the pearlitic transformation in a rehe ated high manganese steel were examined by the isothermal dilatation method, the isothermal magnetization method, and both the optical and the electron microscopic observations. The results obtained were as follows:
    1) From the measured interlamellar spacing of pearlite in an isothermally heated steel, it is consideredth at the growth of pearlite in this steel is similar as that in other carbon or low alloy steels, though the trans-formation rate of this steel is extremely small, because of the high alloy content.
    2) Pearlite in the isothermally heated steel grows with two time-dependent processes, initial rapid growthf ollowing steady slow growth in thermo-magnetic curves. The excellent correlations between the former and the growth of proeutectoid carbide are observed.
    3) Activation energy for pearlitic transformation varies with isothermally heated te mperatures, and increases at temperatures lower than 500°C. Also, the time-dependence of activation energy which varies as the proceeding of growth, is observed.
    4) The activation energy value for pearlitic growth in 500-600°C indicates that the initial growth of pearlite in this steel may be dependent upon either the self-diffusion of Fe atom in γ, or the interfacediffusion of Fe atom at the interface between γ and pearlite.
    5) In the pearlite reaction of high manganese steel, the partitioning of manganese is considered to be an extremely important factor, and the whole transformation behavior is affected by this factor.
  • Effect of Boron, Oxygen, Sulphur, Nickel, Copper and Zirconium on Austenite Grain Size of Steels

    pp. 929-948

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    Boron, oxygen, sulphur, nickel, copper or zirconium was added to high purity iron to study the effect of alloying elements on austenite grain size. The results are summarized as follows;
    1) Boron showed a strong effect upon coarsening the austenite grain size within the range of the concentration from 0.0012 to 0.0127%.
    2) Oxygen had a weak effect upon coarsening the austenite grain size when it was dissolved in austenite or precipitated as wiistite, but an inverse explanation could be made on the effect of wastite from the view point of dissolution of wastite. Further investigation is necessary to clarify the effect of dissolved oxygen and wastite. Alumina type oxygen had a tendency to inhibit the grain coarsening.
    3) Austenite grain size was not affected by the addition of sulphur within the range from 0010 to 0.39%.
    4) Nickel showed a strong effect upon refining the austenite grain size up to about 10%, while it had a effect upon coarsening the austenite grain when the content of nickel was higher than 10%.
    5) Austenite grain size was not affected by the addition of copper within the range from 0.008 to 1.00% but was refined by the addition of 294% copper.
    6) Austenite grain size was slightly refined by acid soluble zirconium within the range from 0.047 to 1.82% while the refining effect was not so obvious within the range where Fe2Zr was assumed to be precipitated.
  • Effect of Cold Working on Creep Properties of 316 Stainless Steel Used as a Fuel Cladding in Fast Breeder Reactors

    pp. 949-954

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    The effect of cold working on creep properties of 316 stainless steel used for a fuel cladding material in fast breeder reactor has been investigated. Specimens rolled by 0 to 30% were tested under various stresses, 4 to 15kg/mm2, at 650°C and 750°C.
    It was observed that the 5% cold-rolled specimen showed the minimum creep rate under low stress at 650°C, however, the non-cold rolled specimen showed the lowest creep rate at 750°C. This could be explained by the creep strain which assisted the recovery of the previous strain due to cold working. The recovery observed by X-ray diffraction was a clear evidence of the above explanation, especially in the case of creep at 750°C.
  • Cleavage Fracture of Iron Single Crystals

    pp. 955-966

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    Iron single crystals with various orientations were tested at low temperatures.
    1) At-196°C, the behaviour of the crystals depended on the orientations of their stress axis. When the angle between the specimen axis and [001] was less than 26°, the specimens fractured by cleavage with prior twinning. Most of the specimens were cleaved at ‹011› type intersection of two twins, but some of them were cleaved by a twin going through the specimen surface. The specimens with the angle between [001] and tensile axis greater than 36° showed slip deformation preceded by twinning. The specimen with tensile axis near [111] was fractured by cleavage after crack opening at twins due to plastic deformation.
    2) The crystals tested at -130°C fractured in ductile manner with one exception.
  • Discrimination of Carbides Morphology by Optical Matched Filtering Method

    pp. 967-971

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    An application of optical matched filtering, which is one of the hologram techniques, to the recognition of patterns is described from the viewpoint of quantitative metallography.
    The results obtained are summarized as follows:
    1) The contour treatment of the input patterns is effective in the recognition of patterns.
    2) The optical matched filtering method was applied successfully to determine the morphology of carbides in a high manganese cast steel.
  • Observation of a Phase with the β-Manganese Structure Precipitatcd in a 25%Cr-28%Ni-2%Mo-0.31%N Austenitic Steel by Electron Probe Microanalysis

    pp. 972-974

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    Two types of phases precipitated in a 25%Cr-28%Ni-2%Mo-0.31%N austenitic steel aged for 2000 hr at 850°C were examined by electron probe microanalysis. One of the phases was identified as a nitride with the β-manganese structure, while the other has been known to be a dichromium nitride, Cr2N. A clear distinction between the β-manganese type nitride and Cr2N could be made from the back scattered electron image.
  • On the Formes of Chromium Compounds in Rimmed Steel with Low Chromium Content

    pp. 975-978

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    An investigation has been made of the forms of chromium compounds in hot-rolled rimmed steel sheets containing 0.02-0.1% Cr.
    The results observed are summarized as follows:
    (1) Besides chromium in solid solution, chromium was identified both in oxide, (FeMn) O·Cr2O3, which is coarse particle, and sulfide, FeS·Cr2S3, which is fine particle, and no chromium and carbide and nitride were found.
    (2) The amount of (FeMn) O·Cr2O3 increases in proportion to the increase in total Cr content while the amount of FeS Cr2S3 is determined mainly by sulfur content regardless of chromium content.
  • Automation of Chemical Analysis of Iron and Steel

    pp. 979-987

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  • Applications of Ultra-High Voltage Electron Microscopy to Science of Iron and Steel

    pp. 988-1005

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  • 抄録

    pp. 1006-1012

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