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

Tetsu-to-Hagané Vol. 63 (1977), No. 14

  • 原点からの再出発

    pp. 2267-2268

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  • Reduction Properties of Raw Materials for Direct Reduction Shaft Furnace

    pp. 2269-2277

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    Reduction tests were performed on eight kinds of pellets produced at the actual pellet plants and four types of lump ores under the condition of the direct reduction shaft furnace, at the temperature range of 700-960°C, with reducing gas composition of H2 55%, CO 36%, CO2 5%, and CH4 4%. Reduction properties of these materials were investigated mainly on three important characteristics, that is, reducibility, generation of fine particles during reduction, and softening behaviour of sample beds.
    The following results were obtained.
    1) The reducibility of the pellets are fairly Well related to the amount of slag or lime addition: the higher iron content of materials, the higher degree of reduction are obtained.
    Decrease of the reducibility with the increase of slag volume or lime addition is dependent on the formation of liquid phase during pellet firing process, where the certain amount of iron oxide is included.
    2) In a reduction test under load, pellets with the high iron content show the higher shrinkage and the indication of clustering is observed in the reduced samples.
    3) The difference of the reduction properties of burden for shaft furnace from those of ordinary blast furnace is also discussed.
  • Classificating Properties and Separating Mechanism of the New-type Air Separator

    pp. 2278-2286

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    The effects of rotational speed of selector blades, number of selector blades, and circulating flow rate of air on classification properties and separating mechanism of a new type air separator (casing dia. 320mm) have been investigated.
    The main results obtained are as follows:
    (1) It is observed that selector blades of the rotor bring about a dead zone of air current in separating many particles and it is recongnized that the classification of this air separtor is carried out in the range where Allen's law holds.
    (2) Cut size: over 20 (90% passing size of fine powder),
    separating efficiency: 70-80% (lime stone)
    60-70% (iron ore),
    pressure drop: max. 320mm H2O.
    (3) The observed values, both cut size (d) and Ur/Uθ4/3, change in a good agreement with theoretical equations developed for the separating mechanism, that is
    d=109Ur/Uθ4/3 (lime stone)
    d=79.5Ur/Uθ4/3 (iron ore)
    (4) An enlarged air separator (casing dia. 1800mm) similar to the experimental one shows the same separating mechanism and calssification properties better than those of other large-scale air separators.
  • Phosphorus Removal from Fe-Cr-C Alloys with CaC2-CaF2 Flux

    pp. 2287-2291

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    ESR experiment was made in which CaC2-CaF2 flux was used as an electro-flux under an inert atmosphere. Fe-C alloys containing Cr up to 64% were remelted. P and N contents as well as O and S ones of the alloys were found to be reduced during the remelting. Simultaneously, carbon pick-up was observed, indicating that CaC2 was decomposed into Ca metal dissolved in CaF2 melt and C in the liquid alloy. The refining ability of CaC2, therfore, was equivalent to that of Ca metal. The degree of phosphorus removal was determined only by the rate of CaC2 decomposition which was evaluated as a function of the feeding rate of CaC2 powder and the activity of carbon dissolved in the liquid alloy. Practical applications of CaC2-CaF2 flux as a new dephosphorizing reagent in refining processes were discussed.
  • Dephosphorization of Fe-Cr-Si Alloys for Low Phosphorous Stainless Steel

    pp. 2292-2298

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    In order to produce low phosphorous stainless steels with superior stress corrosion resistance, the possibility to remove phosphorus by the following two methods for ferro-silicochromium, which is an intermediate product for low carbon ferrochromium, was investigated. Firstly, the evaporation of phosphorus in vacuum was studied by using levitation technique, and secondly, the CaF2-CaC2 flux was used as a dephosphorizer in a plasma melting furnace. Both methods gave the phosphorous content less than 0.01%, which is low enough for the above mentioned purpose, It was found that the higher silicon content in the alloys significantly exxhanced the dephosphorization. These results also encourage the usage Of chromite ore and coke with higher phosphorous contents, if the dephosphorization process is only incorporated to the conventional process for low carbon ferrochromium production.
  • Absorption of Sulphur from Gas Phase to Liquid Slags under Reducing Atmasphere

    pp. 2299-2307

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    The rates of sulphur transfer from gas to liquid slags were studied under reducing atmosphere. Ar-H2S gas mixture was introduced over those liquid slags, such as CaO-SiO2, CaO-Al2O3, and CaO-SiO2-Al2O3 slags at 1550°C.
    The results are as follows:
    1) The rates of sulphur transfer from Ar-H2S gas mixture were proportional to the partial pressure of hydrogen sulphide, and also to the flow rate of the gas mixture.
    2) If those slags were melted in a graphite crucible, the rates of sulphur absorption of binary slags CaO-SiO2 were higher than those of CaO-Al2O3 system.
    3) The rate of sulphur absorption of ternary slags of CaO-SiO2-Al2O3 system in a graphite crucible could be represented as a function of the activities of CaO and SiO2. A linear relationship was obtained between the rate of sulphur absorption and the activity of CaO, with the activity of SiO2 as a parameter. In addition, it was generally observed that the rates increased by increasing the activity of SiO2 with the constant activity of CaO.
    4) In view of other experimental results, it was also clear that the interfacial reaction between a graphite crucible and liquid slags would have some influences on the rates of sulphur transfer. Although the reduction of SiO2 by graphite accelerated the sulphur transfer, the dissolution of graphite into liquid slag retarded it.
  • Bubble Formation at Single Nozzles Immersed in Molten Iron

    pp. 2308-2315

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    A study has been made of the formation of bubbles from single nozzles in liquid iron. The size of bubbles is determined by a pressure pulse technique. Nozzles used in the experiments are of the sizes 0.32-0.67cm in O.D. and 0.12-0.33cm in I.D. The gas flow rate and the oxygen concentration in liquid iron are varied from 0.1 to 36 cc/sec at 1600°C and 0.0040-0.046%, respectively. The experiments are carried out under conditions where the gas chamber volume has no influence on bubble formation. At lower gas flow rates, the bubble diameter (dB) is determined by the nozzle outer diameter (dn0), liquid density (ρ1) and surface tension (σ). At higher gas flow rates, the bubble diameter depends on the gas-flow rate (Vg) and nozzle outer diameter, being independent of the physical properties of the liquid. It is shown that the following equation is applicable for describing the size of bubbles in liquid iron in the whole range of explored gas flow rates.
  • Effect of Free Lime on Disintegration of LD Slags

    pp. 2316-2325

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    The determination of free lime in LD and synthetic slags was done gravimetrically by carbonating free lime under the stream of carbon dioxide and water vapor. The results obtained by this gravimetric method were discussed and compared with those of the chemical wet method, i. e. by use of the tribromophenol extraction-atomic absorption spectrum method. Disintegration by the autoclave expansion test was found to be closely related to the free lime concentration, and LD and synthetic slags containing more than 1wt% free lime were found to disintegrate. Mineralogical studies of LD, synthetic and remelted LD slags were carried out in focus of the free lime phase by means of microscopic and EPMA examinations. From these, the free lime phase containing FeO, MnO, and MgO was microscopically found to be hydrated under the atmospheric condition. Free lime grains present in LD slags were clustering, surrounded by the dicalcium silicate phase, but these were dispersed homogeneously after remelting in air. Free magnesia containing FeO, MnO, and CaO was observed in LD slags containing about 10wt% magnesia. This magnesia phase was neither hydrated in microscopic examinations nor disintegrated by the autoclave expansion test.
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    1. Hydration of Crystallized Lime in BOF Slags ISIJ International Vol.35(1995), No.3
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    3. Determination of Free Lime Contents in Slags by Solution Calorimetry ISIJ International Vol.36(1996), No.Suppl
  • Development and Application of Oxygen Sensors to Steelmaking Operations

    pp. 2326-2334

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    An oxygen sensor with Cr/Cr2O3 reference electrode has been developed and used practically in steelmaking operation. The relation between the dissolved oxygen content at blow off and the conditions of LD refining operation was studied with the help of the data obtained by this cell. Consequently. Al content of killed steels in the ladle, Si content of semi-killed steel, and Mn content of rimmed steel have been precisely adjusted from the dissolved oxygen content measured, because it gives the quantities of the materials to be added at the LD tapping process.
    The main results obtained are summarized as follows:
    (1) The oxygen sensor was successfully applied to practical use in steelmaking.
    (2) Dissolved oxygen contents of the steel in the LD converter are closely related to Mn content and bath temperature as well as to C contents of steel.
    (3) Dissolved oxygen contents are not affected by the “after blows” and the furnace life.
    (4) Because the relation between the dissolved oxygen at blow off and Al content of killed steel in ladle has been clarified, more precise adjustment of Al content in ladle became possible, compared to the previous method using carbon-oxygen relations.
    (5) Because oxygen content of steels are closely related to the Si content of Si-semi-killed steels and Mn content of rimmed steel, precise adjustments of the crow of Si-semi-killed ingot top and the degree of rimming action of steels became possible.
  • Effect of Cold Rolling by Grooved Rolls upon the Formation of Recrystallization Texture of 3% Silicon Steels

    pp. 2335-2344

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    In this experiment, effects of groove-rolling developed by the present authors on the mechanism of recrystallization, on grain growth and on the formation of texture during annealing were studied. The experimental results are as follows.
    When the specimens groove-rolled under high rolling reduction were annealed, their (100) [011] texture was favorably maintained in the entire process of annealing, except that a temporary decrease in (100) texture was noted during primary recrystallization. At a 60% groove-rolling reduction or above, a grain size reduction and increase in the fraction of (100) grains were noticed. The reduction by groove-rolling applied during cold rolling is exceedingly effective in the development of annealed texture. In fact, (110) [001] texture was observed to develop at a grooved roll reduction of 40-50%; (100) [hkl] texture at 50-60% reduction; and (100) [011] texture at 70% or above, each on annealing for twenty hours at 1170°C. The (100) [011] texture first formed during cold rolling was further developed on annealing into a higher level of the same texture.
  • Load Analysis of Main Driving Motor of Spiral Pipe Mill

    pp. 2345-2354

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    The process of spiral pipe mill consists of preparation, forming and welding. In this study, resistance forces in each working process are calculated theoretically, and the load, which is required to carry strip and pipe, is also taken into consideration. The total load is compared with the indicated load on main driving motor of spiral pipe mill, and both values are shown to agree well each other. Dynamical behavior in each working process in the spiral pipe forming is also analyzed.
  • Continuous Heating Transformation of Spheroidal Graphite Cast Iron

    pp. 2355-2361

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    This study is aimed to make clear the effect of heating rate on A1 transformation of spheroidal graphite cast iron by dilatometric and metallographic methods.
    The dilatation-temperature curve is affected markedly by the heating rate and the initial microstructure. In the case of ferritic structure, dilatometric curves show only expansion during the transformation instead of contraction in steel and in pearlitic structure. A1 transformation temperature (Ac1s and Ac1f) is shifted to higher temperature with increase of the rate of heating in ferritic structure than in pearlitic structure. In ferritic iron, the volume fraction of γ phase is proportional to transformation time at a constant rate of heating, and γ phase forms mainly around the graphite nodules at higher rate of heating but it forms along the grain boundaries of ferrite at lower one. The continuous heating transformation curve (CHT) appears higher in temperature and longer in time than isothermal austenitizing curve (TTA).
  • The Effect of Temperature and Strain Rate on the Tensile Deformation Behaviour of Austenitic Steel

    pp. 2362-2371

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    Tensile deformation behaviour of Fe-Cr-Ni and Fe-Mn-Cr austenitic steels with various combinations of carbon and nitrogen contents was determined by means of tesile testing in the range of temperatures from room temperature to 700°C with various strain rates.
    Tensile strength and yield strength of low carbon austenitic steel decrease gradually as the temperature increases and austenitic steel with carbon content of more than 0.3wt% shows a rapid increase of work hardening rate in the temperature range from room temperature to 200°C and in this temperaturc range, serration is observed in stress-strain curves. It is assumed that this serration is associated with the interaction of interstitial atoms (such as carbon) and dislocations. When temperature reaches 450°C, another type of serration appears, but this serration gives a smaller work hardening rate compared with the one observed at temperatures from room temperature to 200°C. This observation proves that serration is closely related with tensile deformation behaviour.
  • Effect of Grain Boundary Migration and Recrystallization on the Creep Strength of Inconel 617

    pp. 2372-2380

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    A study has been made of the effects of grain boundary migration and recrystallization on the creep strength of the commercial Ni-22% Cr-12% Co-9% Mo alloy (Inconel 617) at 1000°C.
    Migrating grain boundaries caused a dissolution of carbides, resulting in carbide free zones behind them and in recrystallized grains. Notable grain boundary migration and recrystallization were observed preferentially on longitudinal grain boundaries in the specimens strained by more than 10% (tertiary stage) and they were considered to affect the creep strength in those specimens.
    Decarburized specimens being free of grain boundary carbides exhibited significant grain boundary migration, and this fact implied a suppression of grain boundary migration by grain boundary carbides. A reduction of the creep strength by decarburization was explained in terms of a diminishing of these carbides contributing to depress the action of grain boundaries.
    Partial recrystallization was observed in the specimens given a slight cold-rolling of 7.5% and subsequent annealing at 1000°C. It was shown that recrystallization not only decreased the strengthening due to cold work but also degraded the strength by the associated microstructural changes, i. e., coarsening of carbides and formation of new grains or subgrains.
  • High Temperature Aging Structures of Ni-20Cr-20W Alloys

    pp. 2381-2390

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    High temperature aging structures and age hardening of Ni-20Cr-20W alloys developed as the superalloys for the nuclear energy steelmaking, and effects of C and Zr additions to the alloys and the effect of preheat treatment on these properties were studied.
    M6C, α-W and two kinds of M23C6 having different lattice parameters were found as precipitates in the alloys. M23C6 whose lattice parameter was around 10.7A precipitated in the early stage of aging at 700°C-1150°C, and the carbide changed to M6C at higher temperature than 1000°C, but it remained as a stable carbide at lower temperature than 900°C.
    α-W precipitated at 800°C-1100°C after precipitation of M23C6 and it disappeared with increase of M6C. M23C6 having the larger lattice parameter (10.9Å) precipitated transitionally in aging stage of 26×103 in Larson Miller parameter at 900°C and 1000°C.
    Age hardening corresponded to the precipitation of M23C6 and it was reduced by the double pre-heattreatment.
    Zr addition and amount of C influenced on the aging structure and age hardening. Zr seemed to be a favorable element to stabilize the carbide.
  • Problem on Determination of Hydrogen in Steel Using Graphite Crucible

    pp. 2391-2395

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    For the determination of hydrogen in steel, the high-frequency fusion impulse-furnace fusion method using the graphite crucible is currently employed because of its rapidity. Comparing with the results by the heat extraction method using no graphite crucible, those by above methods agree with standard values in the case of standard samples stainless steel but are inclined to be higher in the case of samples taken from melts (mold samples). In mold samples, fine cracks and blow-holes are often contained where water is included during the storage and preparation of samples. As the result of the reaction between the included water and the graphite crucible (water gas reaction), involved hydrogen is accumulated to the resultant value of hydrogen.
    For elimination of th included water, authors invent the pre-heat device. The included water in samples eliminated by the heating (300-350°C) and at the same time, the diffused hydrogen is collected to determine.
    Using the improved method, the determination of hydrogen is carried out exactly although the sample contains some blow-holes. This method requires only eight minutes for one determination and gives the good accuracy (standard deviation=0.1ppm H2 at 2.5ppm).
  • Theoretical Bases of Metallurgical Process

    pp. 2396-2401

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  • Some Talks on the Ocasion of the 10th Anniversary of Japan-USSR Joint Symposium

    pp. 2402-2406

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  • 報告

    pp. 2407-2419

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    x

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    1. 日本鉄鋼協会第102回講演大会 講演概要集(I) その7 Tetsu-to-Hagané Vol.67(1981), No.12
    2. 日本鉄鋼協会第93回講演大会講演概要 Tetsu-to-Hagané Vol.63(1977), No.4
    3. 抄録 Tetsu-to-Hagané Vol.64(1978), No.12
  • 抄録

    pp. 2420-2429

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