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

Tetsu-to-Hagané Vol. 55 (1969), No. 13

  • Degradation of Sintered Ore During Reduction

    pp. 1107-1118

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    The results of several experiments on the degradation of sintered ores during reduction are summarized as follows:
    (1) The initiation of cracks takes place, when the reduction of hematite commences.
    (2) Degradation does not occurs if hematite has been converted to magnetite by the previous heat treatment.
    (3) If the converted magnetite are re-oxidized to hematite, the degradation appears again.
    (4) The changes of mineral phases during reduction are as follows:
    a) The original hematite was quickly converted to co-existent phase of hematite and magnetite.
    b) Accicular calcium-ferrites were coagulated during reduction.
    c) The original magnetite crystals were broken down.
    (5) The influences of reducing conditions can be summerized as follows:
    a) The degradation did not proceed further after 90min.
    b) The higher the CO content of reducing gas, the greater the degradation.
    Based on these results, the sequence of degradation of sintered one is discussed.
    The stress which initiates the cracks is considered to be generated from the quick alteration of mineral phases and shape of iron-oxides.
    x

    Readers Who Read This Article Also Read

    1. 表面処理・その他 Tetsu-to-Hagané Vol.52(1966), No.11
    2. Kinetic Study of the Decarburization of Liquid Iron Tetsu-to-Hagané Vol.52(1966), No.12
    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • On the Pelletizing of Limonite Ore from Shiretoko in Hokkaido

    pp. 1119-1133

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    Limonite from Shiretoko Peninsula, Hokkaido, has been examined as to its mineralogical properties, suitability for pelletizing, and properties of pellets obtained therefrom.
    Results are as follows:
    (1) The are consists of globular grains of irregular shape, which shows identical X-ray diffraction patterns as the artificial goethite.
    (2) The value of work index of the limonite is 4.80.
    (3) Green pellets having the crushing strength of 2.0kg/pellet or above can be obtained only when pellet feed contains more than 60 per cent of under 325 mesh particles.
    (4) The high temperature crushing strength increases remarkably at 1100°C, so that a shaft furnace or a rotary kiln can be used for the firing of the pellets.
    (5) Pellets of highest mechanical strength can be obtained by firing the green pellet containing 1% bentonite and 1% lime as binder at 1300-1350°C.
    (6) The crushing strength of the pellets thus obtained is >500kg/pellet, the tumbler index >95%(1mm over), the shatter strength 100%, porosity about 20% and reducibility (JIS specification) about 60%.
  • The Rate of Dissolution Iron Into Liquid Fe-C Alloy

    pp. 1134-1141

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    The rate of dissolution of solid iron into Fe-C liquid alloy was studied in a temperature range from 1200 to 1420°C and for a range of initial carbon content from 4.0 to 4.3%.
    The rate of dissolution was determined from the change in the bath composition. It was presumed that the data were consistent with a model based on simultaneous heat and mass transfer in the boundary layer between solid and liquid. Mass transfer coefficient estimated from this model was found to be in agreement with an existing dimensionless correlation for mass transfer.
    In the explored temperature range, the thickness of diffusion boundary layer was 5×10-3-10-2cm.
    This value was considered to be a reasonable parameter in the model of scrap melting developed recently by the authors.
  • Absorption Rates of Blown Bubbles into Molten Metal

    pp. 1142-1151

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    The absorption of bubbles into a liquid metal was conducted in a 40mm ∅; sinter mullite crucible at 1000°C. Oxygen was blown through the 1.2mm ∅; nozzle of a silica tube into 150-700g silver.
    The depth of the immersed nozzle H was 9-64mm. The oxygen flow rate Vg was 0.88-3.23 Ncc/sec. The absorption rates of blown oxygen into molten silver were measured by the ZrO2·CaO solid electrolyte galvanic cell. By estimating the diameters and rising velocities of bubbles, the metal phase mass transfer coefficients were obtained. At the smaller depth, the observed values were higher than the theoretical ones by Higbie's model. As the depth became larger, the observed values approached to the theoretical ones. At the lower oxygen concentration, the absorption efficiency of oxygen was very high, but towards the saturated content of oxygen, it dropped rapidly. These phenomena were explained theoretically. In conclusion, the connection with the practical problems was discussed, especially with the oxygen utilization coefficient in open-hearth furnace and converter.
  • Transport Phenomena of Supersonic Jet in Oxygen Top Blowing Converter

    pp. 1152-1163

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    In order to clarify the effects of gas temperature around a jet on the characteristics of supersonic jet in LD converter, theoretical analysis on the transport phenomena of supersonic jet is proposed in this work.
    Axial and radial distributions of velocity, temperature, mass fractions and density for turbulent compressible free jet are determined under consideration of the mixing in a jet and the flow rate of gas entrained from the surrounding. It is found that the effects of gas temperature around a jet on these distributions are remarkable.
    Moreover, relations between the operating variables (axial distance from exit of nozzle and back pressure) and the behaviour of supersonic jets are obtained from numerical calculations with the aidof digital computer.
    x

    Readers Who Read This Article Also Read

    1. Effects of Characteristics of Supersonic Jet in the Operations of Oxygen Top Blowing Converter Tetsu-to-Hagané Vol.55(1969), No.13
  • Effects of Characteristics of Supersonic Jet in the Operations of Oxygen Top Blowing Converter

    pp. 1164-1175

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    Theoretical equations determining the profile of cavity in steel bath are proposed based on the previous analysis on the mixing problems involving momentum, energy and mass transfers in turbulent axially symmetric compressible flow of supersonic jet.
    As the results, the change of cavity profile caused by the variation of the conditions of surrounding gas around a jet and characteristics (velocity, temperature and compositions) of a jet impinging on the surface of cavity can be estimated with the progress of blowing time. During the blowing time, the amount of oxygen which does not arrive on the surface of cavity are obtained from the relations between the radial distributions of oxygen in a jet and cavity profile.
    Also, the operating conditions at the limit of occurance of shock wave in a jet impingiug at stagnation point of cavity and the problems of mutual interference of cavities are analyzed in this paper.
    x

    Readers Who Read This Article Also Read

    1. Transport Phenomena of Supersonic Jet in Oxygen Top Blowing Converter Tetsu-to-Hagané Vol.55(1969), No.13
  • The Rate of Absorption of Nitrogen in Liquid Fe-O-J and Fe-S-J Alloys

    pp. 1176-1182

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    The rates of nitrogen absorption in the ternary liquid iron, Fe-O-J, at several oxygen levels were measured at 1600°C. The results show that chromium and vanadium clearly increase the apparent mass transfer coefficient in any oxygen levels, as chromium and vanadium increase up to about 2%. Manganese and nickel have virtually no effect on the apparent mass transfer coefficient. The deoxidizing elements, such as chromium and vanadium, act as counter-poison for surface active oxygen. However, it is reasonable to consider that oxygen at the gas-metal interface mostly remains near interface, andacts as a resistant substance, even if the deoxidizing elements are present.
    It is further observed that carbon, manganese and silicon in the ternary liquid iron, Fe-S-J, have virtually no effect on the apparent mass transfer coefficient, probably because of the lower affinities of these elements to sulphur and the weaker effect of sulphur on the rate of nitrogen absorption than oxygen.
  • Study on the Dephosphorization in Alloy Steel

    pp. 1183-1192

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    The dephosphorization in alloy steel was investigated for Fe-C-Cr-P alloy chiefly with high basic and fluid slags.
    At first, the experimental heats were made by induction melting the Fe-Cr-P alloys in lime crucibles under various oxidizing conditions. In this case, the relation between the contents of chromium and phosphorus nearly followed its equilibrium relation calculated under the condition of both a4CaO·P2O5=1 and aFeO·ECr2O3=1, and the dephosphorization in a few per cent chromium steel was not improved in this condition.
    Then in order to investigate the effects of CaF2 and FeO concentration in the slag and temperature on the dephosphorization, the Fe-C-Cr-P alloys were melted in MgO crucibles with CaO-CaF2-FeO slags.
    For dephosphorization in alloy steel, less oxidizing condition in slag is desirable to restrict the oxidation loss of alloy constituents. As a result of a series of experiments, it was found that the synthetic slag at CaO: CaF2=5: 5 could fairly promote the dephosphorization at the least concentration of iron oxide, and in the course of its process, for the medium carbon alloy steel containing several per cent chromium, the oxidation loss of carbon and chromium could be remarkably restricted.
  • Effect of the Alloying Elements on the Solubility of Oxygen in δ-Iron

    pp. 1193-1198

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    Non metallic inclusions change their composition in solid iron during annealing at high temperatures.Therefore, it is desirable to know the effects of the alloying elements on the oxygen in solid iron. This experimentwas carried out to know the effect of the alloying elements on the solubility of the oxygen and to determinethe interaction coefficients of oxygen in δ-iron. The crucible assembly was lowered very slowly underpurified argon gas in Tamman furnace and the equilibrium between solid iron and liquid was observed.The relation of the distribution ratio of oxygen in Fe-O system (Lo′) and in Fe-O-X system (Lo) is
    log Lo=log Lo′+log f(X)l/f(X)S
    where f(X)S and f(X)lare the interaction coefficients in solid and liquid iron respectively. By using the relation, we can get the interaction coefficients in solid iron. These results are as follows:
    log f(Mn)S=-1.83 [% Mn] <0.15%
    log f(Cr)S=-0.23 [% Cr] <0.5%
    log f(Si)S=-12.14 [% Si] <0.1%
    log f(V)S=-1.71 [% V] <0.3%
    log f(Ni)S=-0.105 [% Ni] <1.0%
  • On the Quantitative Observation of Solidification Structure and Segregation in Steel Ingot by the Autoradiographic Method

    pp. 1199-1211

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    Some experiments were made to establish a method of quantitative observation of solidification structure and segreagtions in steel ingots by measuring the blackness of autoradiographic images of the ingots. Furthermore, this method was applied to some practical and experimental steel ingots.
    The results of these investigations can be summarized as follow:
    (1) Blackness of the autoradiograph is directly proportional to the tracer content in the sample.
    (2) Maximum points of blackness in the microphotometric trace correspond to the positively segregated areas in the interdendritic regions, and minimum points, to the negatively segregated areas in the dendrite arms. Microsegregation of the tracer can thus be observed quantitatively, and also degree of fineness of solidification structure can be expressed by the number of the maximum or minimum points within a given distance.
    (3) Reproducibility of the results is fairly good under the fixed experimental conditions. Therefore, this method can be applied to the quantitative observation of solidification structure and segregations of steel ingots within the limits of resolving power of the autoradiographs.
    (4) By the application of the method to some practical 20t ingots and experimental small ingots, several informations were obtained about solidification structure, microsegregation of Ta and Cu, and “inverted V” segregates.
    x

    Readers Who Read This Article Also Read

    1. 表面処理・その他 Tetsu-to-Hagané Vol.52(1966), No.11
    2. Kinetic Study of the Decarburization of Liquid Iron Tetsu-to-Hagané Vol.52(1966), No.12
    3. II 連続鋳造の凝固について Tetsu-to-Hagané Vol.56(1970), No.4
  • Effects of Nonmetallic Inclusions on the Hot Torsional Deformability of Rimmed Steels

    pp. 1212-1218

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    The effects of nonmetallic inclusions on the hot torsional deformability were investigated on the specimens cut from the slubs of rimmed steels (12t). The kinds and cleanliness of nonmetallic inclusions were examined in the test part of each test piece. The hot torsional tests were carried out at 1000 and 1200°C at the strain rates of 15·2, 1·67×10-2 and 5·81×10-4sec-1.
    The results obtained were as follows:
    (1) The effect of MnS on the hot torsional deformability was most remarkable. The relation between the cleanliness of MnS and the number of twist to failure was changed in the form of hyperbola. When the cleanliness was more than about 0·075%, the number of twist to failure was small, and it decreased slowly with increasing cleanliness. When the cleanliness was less then 0·075%, the number of twist to failure remarkably, increased by decreasing the cleanliness. The number of twist to failure did not depend on the strain rate, but on the strain. The cleanliness is so defined as to increase when the density of inclusions increases.
    (2) In case of the oxide-type inclusions which were hardly deformed during the hot torsional deformation, the initiation of the cracks from them depended on their shapes and sizes, the deformability of matrix, and the strain rate.
  • Recrystallization Textures of Low Carbon Rimmed Sheel Steets

    pp. 1219-1228

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    It has been shown by many research workers that a good drawability or a high strain ratio value can beattained in properly processed aluminum killed steel sheets and the higher density of near {111}‹112› or {111}‹110› component in the recrystallization textures is responsible for the higher strain ratio values of thesheets. The authors have recently obtained high densities of the near {111}‹112› and {111}‹110› componentsin the recrystallization texture of a rimmed steel sheet.
    The massive transformation structure was obtained in the hot-strip of a rimmed steel (C=0.06wt%) byquenching from 920°C. After ageing at 200°V-250°C for 3 hr, the strip was cold-rolled 70% and finallyannealed at 700°C or 800°C in wet hydrogen or argon atmosphere. The (200) pole figure of the finallyannealed sheet showed strong intensity maxima around the poles corresponding to the near {111}‹112› or {554}‹225› and {111}‹110› orientations. The pole density of {222} parallel to the sheet plane divided bythat of a random specimen was 6.7-7.1.
    The results are discussed in relation to the inhibition of the recrystallization process by finely dispersed Fe3C particles.
  • Effects of AlN Precipitation on Mechanical Properties of α-Iron

    pp. 1229-1242

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    Two series of Fe-0.01, 0.03, and 0.1% Al-0.015% N alloys with either 0.01 or 0.002% C, were usedto study the states of AlN precipitates and their effects on the yield point of x-iron. Results obtained areas follows.
    (1) AlN is mostly precipitated in the temperature range between 800 and 900°C during isothermalafter solution treatment.
    (2) Carbon content affects the amount, shape, size, and dispersion of AlN precipitates.
    (3) Variation of yield point is well explained by the individual contributions of AlN precipitates andof dissolved nitrogen.Investigation on ductility and work hardening of extra low carbon Fe-Al-0.01% N alloys with Al contentsvarying from 0.005 to 1% leads to the following conclusions.
    (4) The behavior of dissolved nitrogen as revealed by internal friction suggests that the reversion of AlNprecipitation occurs.
    (5) In the same heat tretament that will cause the intergranular brittle fracture, ductility can be improvedby fixing the more amount of nitrogen. In the ductile states, the contribution of AlN precipitates toductility is the greater, the smaller their effect on hardening is.
    (6) Grain size is the main factor influencing work hardening; nitrogen in solution or fine AlN particlesincrease the work hardening rate, while grown precipitates and quenched-in dislocations decrease it.
  • Resistometric Study of Precipitation in Maraging Steels

    pp. 1243-1254

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    Precipitation characteristics in 18%, 20% and 25% nickel type maraging steels were investigated by measuring the changes in electrical resistivity at liquid nitrogen temperature. Generally, the changes in resistivity are large in the remarkably precipitation-hardened steels, and the aspect of the changes in resistivity well coincides with that of the changes in tensile strength.
    In the 18% nickel type maraging steel, the precipitation kinetics and its mode are assumed to be different in the temperature ranges above about 425°C and below. Consequently, the precipitates formed in the temperature ranges also seem to be different with each other. Activation energy for precipitation is about 35kcal/mol, and it can be deduced from this result that the precipitating atoms may diffuse through martensitic matrix with the help of some kinds of lattice defects. However, at the stage of over about 70% in total resistivity change, the activation energy seems to be increased to 44-49 kcal/mol.
    In the case of 20% and 25% nickel type maraging steels, the resistivity increase, assumed to be due to the formation of cluster zone, was found at the early stage of precipitation. Activation energy for the formation of cluster zones was determined as 55-65 kcal/mol but, in the early stage of the formation, the activation energy was calculated as about 35kcal/mol. The precipitation rate in the 25% nickel type maraging steel was faster than that of the 20% nickel type maraging steel and the maximum precipitation-hardened state appeared in the stage of the growth of cluster zones. In comparatively higher aging temperature range, stable austenite, retained even in liquid nitrogen temperature, was formed and resulted in resistivity increase. The formation of austenite was more easily in the 18% and the 25% nickel maraging steels than in the 20% nickel maraging steel, and was accelerated by cold work.
    Precipitation rates in nickel maraging steels were accelerated by cold work but its effect was not so significant as might be expected.
  • Microsegregation of Cr and C in 17%Cr Stainless Steel

    pp. 1255-1262

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    The microsegregation of C and Cr in type 430 stainless steel as cast state was investigated with EPMA. Chromium content [Cr] in α-phase was 18.5% and that in γ-phase 17.8%, but carbon content [C] in γ-phase was 10 times more than that in α-phase. The phase boundary where Cr-carbide precipitated was enriched with C and Cr.
    These results suggest that Cr does not segregate so much as expected from the equilibrium phase diagram during phase transformation of as cast 17% Cr stainless steel and the thermodynamic unstability of each phase can be offset by C segreagation in them. The analysis of C in stainless steel with EPMA was also discussed.
  • Determination of Sulfide in Steel by Electrolysis Method

    pp. 1263-1269

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    In order to determine sulfides in steel, electrolyte dissolution of matrix and extraction of sulfides from the electrolytic residue were studied.
    The results are as follows:
    (1) The use of small quantity of citric acid-sodium citrate solution of pH 4.0 as electrolyte has made the extraction procedure more rapid and easy to operate. Furthermore the extraction of sulfides can be quantitatively made.
    (2) By treating the residue with hydrogen peroxide and the subsequent determinations of dissolved metal ions, MnS is determined with reasonable accuracy but FeS not.
  • The Emission Spectrophotometric Analysis of Steel Sample Prepared by Ar-Arc Melting Furnace

    pp. 1270-1276

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    On applying the emission spectrophotometric analysis to steel, we have usually determined using complicated corrections and layer-separated calibration curves in accordance with the difference ot its metallurgical history. Besides it couldn't be applied to irregular shaped samples such as the chipped and wire.
    The following method was examined to solve above problems: melting irregular shaped samples such as the chipped, block and wire by Ar-arc melting furnace, casting as the bottom and determining by the emission spectrophotometric analysis.
    It was showed that this method didn't require the correction by its metallurgical history and was satisfactory in regard of precision and accuracy.
    Significant improvement in operation efficiency is expected by simultaneous determination of many elements by this method, compared with the chemical analysis as before.
  • 孔型圧延

    pp. 1277-1288

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