Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 42 (1956), No. 12

  • ON THE ACTIVITIES OF Cr AND C IN MOLTEN Fe-Cr-C ALLOYS

    pp. 1095-1101

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    Constructing the following electrode concentuation cell, the author measured the electromotive force corresponding to the Change in Cr and C in Fe-Cr-C alloys at about 1, 540°C:
    From the following equation the activity of Cr in this alloys was determined for the range of Cr<30% and O<C<Sat.
    Fe-Cr binary alloys obey the Raoult's law but Fe-Cr-C alloys show a gradually negative deviation from the Raoult's law on addition of C. and the effect of C on the activity coefficient of Cr was discussed using interaction parameter rccr. In addition, the effect of Cr on the activity coefficient of C was also discussed. Furthermore, behavior of Cr-oxide in molten slag was considered from oxygen potential that controls the system. And the decarburization limit in Fe-Cr-C alloys was calculated from the experimental results.
  • AERODYNAMIC CONSTITUTION OF OPEN-HEARTH FURNACE (II)

    pp. 1102-1106

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    Flow patterns in semi-Venturi, Maerz and the single air-uptake design with the single oil burner were studied by means of water models.
    Essential flow pattern in the furnace chamber seems to be same in any design. Almost whole central cross-section of chamber is covered with a pair of (JL-shaped) vortices flowing, as Halliday and Philip pointed out in gas-fired Maerz design, upwards along the back and front walls, inwards along the ceiling and downwards at the center of the furnace.
    In the vertical section along the furnace center line, the flow forms a large recirculation, as Halliday and Philip showed in gas-fired semi-Venturi design. The lower part of this recirculation consists of the main furnace flow and the upper part a return flow under the ceiling.
    The return flow runs against the new air flow under the incoming end of the ceiling and makes the air flow down toward the burner jet to promote mixing of fuel and air.
    Differences of flow patterns among these designs exist in the mechanism of mixing at the incoming end. Double air-uptakes, producing JL-shaped air flow, promote mixing at the upper surface of the burner jet. The sigle air-uptake adds mixing under the burner jet.
    The fact suggests the fitness of single air-uptake design to the oil fired open-hearth furnace.
  • IMPROVEMENTS OF OPERATION BY REMODELLING OF THE TRIPLE-FIRED INGOT-REHEATING FURNACE

    pp. 1106-1111

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    Summarized are the details of remodelling a triple-fired furnace which heats ingots of 400mm square or larger, together with the improvements obtained and the further problems to be overcome. The remodelling consisted mainly of increasing space of the bottom-heating zone, changing skid pipe construction, introduction of automatic control and etc. Through which reduced slag accumulation, less temperature gradient within an ingot and imptoved thermal efficiency have been realized.
    Actual operation of the furnace have indicated the following teints as a clue to further improvements:
    (1) Number of supports of skid should be kept to a minimum and width of the skid should be taken as wide as possible so that the ingots might sufficiently heated from the bottom side.
    (2) Space of bottom heating zone should be large enough giving heat release of approximately 100×103 kcal/m3h.
    (3) To avoid a burning on ingot ends, large capacity burners should be arranged directed to the middle of ingots.
  • STUDIES ON CEMENTITE CRACKS OF HIGH CARBON STEEL (I)

    pp. 1111-1117

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    This investigation deals with the causes of cavities which are occasionally observed at the centre of the rolled high-carbon bearing steel.
    Conclusions are as follows:
    (1) When some pressed or hammered billets are cooled down, very fine cracks, the width of which are less than 1/10μ, are formed in Acm cementite. These "Acm cementite cracks" are considered to be caused by the super-saturated hydrogen contained in the billets (hydrogen content are above 3.0cc/100) at the temp of below 200°C.
    (2) These "Acm cementite cracks" grow to cavities during rolling process.
    (3) These "Acm cementite cracks" can be observed in the form of macro-hair-cracks by etching of HCl, but cannot be observed by etching of oxidizing solutions like HNO3 and ammonium persulphate.
    (4) These "Acm cementite cracks" cannot be observed in the form of flakes on fractured surface as far as the billets are simply cooled down.
  • STUDY ON CARBIDES IN PRACTICAL SPECIAL STEELS BY ELECTROLYTIC ISOLATION (II)

    pp. 1118-1122

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    The present report deals with a study on carbides in a high C-high Cr die steel(2.25%C, 12.03%Cr) by electrolytic isolation technique as reported before (J.I.S.I.J. 41, 1955, p 1188).
    In the investigation of tempering of the die steel, a specimen (0.59% C, 4.73%Cr) named "matrix steel" was used, of which composition is similar to the matrix of the die steel at 950°C, in order to remove the interference of undissolved carbides in the quenched structure.
    The results obtained were as follows:
    (1) In the annealed state, carbides in the die steel are (Cr, Fe)7C3 contained 43.0%Cr, and amounted to about 26 wt %.
    (2) With the rise in quenching temperature, the carbides dissolve into austenite and its contents of C and Cr come up to 0.6% and 4.4% respectively, at 950°C.
    (3) The carbide precipitated in the steel by tempering at above 650°C is (Cr, Fe)7C3. But the precipitated carbide by tempering at 40-500°C shows (Fe, Cr)3C type pattern. It is expected that these two kinds of carbides coexist at 550-650°C, and carbide reaction (Fe, Cr)3C→(Cr, Fe)7C3 takes place in this tempering temperature range.
  • THE TRANSFORMATION OF BALL-BEARING STEEL

    pp. 1123-1127

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    The authors studied the continuous cooling and isothermal transformatlon of ball-bearing steel after austenitizing at 1050°C for 30min. The results were as follows. (1) The begin-ning curve of pearlite transformation during continuous cooling calculated by Pumphry-Jones method were found to be in reasonable agreement with those determined experimentally. (2) In the products of continuous cooling transformation, no primary cementite and bainite were found, when the C and Cr contents were richer, while some primary cementite and bainite were found, when the C and Cr contents were poorer.
  • STUDIES ON ANISOTOROPIC MK PERMANENT MAGNET (II)

    pp. 1127-1132

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    The magnetic properties in the anisotoropic MK magnet alloy has been proved to be sensitive to the heat treatment. Effects of solution treatment, cooling conditions in magne-tic field, and aging treatment on the magnetic properties were examined on the specimens of representative composition, and the optimum heat treatment was determined as follows:
    The specimens are solution-treated by heatng for 10 or 20 minutes at 1200 or 1250°C, and cooled in a magnetic fleld of 1500 oersteds or so. The optimum cooling rate for mag-netic treatmnent is 1°C/sec when going from 900 to 800°C The action of the field is effective from the Curie point to 150°C below. In age hardening, the alloy is held for 1 or 3 hours at 600 or 625°C. The magnetic properties can be improved by the growth of columnar cry-stals. On the specimens subjected to the optimum heat-treatment, any precipitation cannot be discerned. It is suggestive that the magnetic anisotropy and high coercive force of this alloy associated with the subdivision of materials by needle-like pseudoprecipitations directed by the magnetic cooling in the field and developed during aging.
  • STUDY ON TIMKEN 16-25-6 TYPE HEAT-RESISTING ALLOY (III)

    pp. 1132-1138

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    Change of the properties during tempering (0°-1000°C) of the solution-treated (1250°C×1h. W.C.) Timken 16-25-6 alloy were studied by measuremnt of hardness, differential dilatation, specific heat, electric resistance and microstructure.
    By electron microstructural studies, X ray diffraction analysis and chemical analysis of electrolytically separated residues, the microconstituents of the aged (550°-900°C) Timken 16-25-6 alloy were studied.
    The results were summerized as follows:
    (1) Two Stages of contraction, heat evolution and decrease of electric resistance at 500°-550°C and 750°C-1000°C by the precipitation were observed during tempering of the solution-treated Timken alloy. The tbmperature range and the amount of changes of the latter was greater than that of the former. It seemed that at least there were two kinds of precipitates at 700°-1000°C and the transition temperature of these was at about 825°C.
    (2) From the dilatation change, it seemed that the precipitate below 600°C dissolved once, and at above 700°C another precipitation occured, but the precipitate above 800°C existed with the precipitate below 800°C.
    (3) The microconstituents of Timken 16-25-6 alloy were composed of double carbide M4C; {(Cr, Fe, Ni)3Mo1}C below 800°C and double nitride CrMoNx; {(Cr, Fe, Ni)1Mo1}N1 as well as double carbide M6C; {Cr, Fe, Ni)5Mo1} C above 800°C.
    No evidence was found of the formation of sigma phase in this alloy.
  • DER NIEDERSCHACHTOFEN

    pp. 1139-1152

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  • 抄録

    pp. 1153-1158

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