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

Tetsu-to-Hagané Vol. 82 (1996), No. 10

  • Removal of Copper from Iron-based Scraps by O2-Cl2 Gas Mixtures

    pp. 799-804

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    A new technique for removing copper from iron-based scrap has been proposed. When iron-based scraps containing copper were placed in atmosphere controlled by O2-Cl2 gas mixtures, copper was chloridized to evaporate, whereas iron was oxidized to remain in the form of solid. The evaporation rate of copper chlorides was determined by the transport of chlorides across the boundary layer. Thermodynamic and kinetic consideration gave the optimal condition for removing copper, that is, the temperature of 1100K and the gas composition of O2-10%Cl2.
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  • Mechanism of Inner Crack Generation of Formed Coke during Carbonization

    pp. 805-810

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    The inner crack of formed coke (FC) causes degradation of coke particles during the transportation and results in low permeability in the blast furnace. Mechanism of inner crack generation of FC during carbonization was investigated by in-situ observation using of a furnace equipped with X-ray generator. The in-situ observation of formed coke elucidated that the inner crack was generated at the semi-coke temperature region with decrease of the radial temperature gradient. The crack was observed at the high heating rates or at the heating patterns with keeping temperature above the re-solidification temperature of FC. Thermal stress analysis indicated that the plastic strain at the re-solidification remains and causes the inner crack at the decrease in temperature gradient. The heating pattern with small temperature gradient at the re-solidification temperature was suggested to prevent inner crack generation.
  • Effective Use of Pisolite Ores Based on Structure Design of the Quasi-particles in Sintering Process

    pp. 811-816

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    To use pisolite ores as raw materials in iron ore sintering process, some effective utilization methods were investigated. Main results obtained are summarized as follows:
    (1) With increase in the pisolite ores in the raw materials, productivity and yields of the sinter products become worse; on the other hand reducibility and reduction degradation index of the products are improved.
    (2) For the purpose of improving the properties of the sinter products, it is most favorable to make quasi-particles having duplex structures; inner core is granulated by the raw mixture containing the pisolite ores and outer shell is coated with fine coke and high grade iron are fines.
    (3) In addition to the making of quasi-particles with the duplex structure, segregation charge of the coke breeze in the sintering bed further improves the productivity and shatter strength of the products.
    (4) Improved properties of the products, such as reducibility and reduction degradation are attributed mainly to the sinter structures and mineral phases constituting the microstructures.
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  • Degradation of Hematite Powder during the Fluidized Bed Reduction with CO-CO2 Gas Mixture

    pp. 817-822

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    The degradation was observed during the reduction of hematite powder (70-140mesh) to magnetite with CO-CO2 gas mixture by a fluidized bed. The effects of reduction temperature, gas velocity, reduction time by fluidized bed, and the other on the degradation were investigated. The degradation was not observed for sample without reduction. The degradation was most significant in the reduction at 700°C, and the amount of the degradation decreased during reduction at higher temperature than 700°C. The amount of degradation increased with an increase of gas velocity, but the amount of the degradation did not increase over the gas velocity 0.44m/s. Next, the amount of the degradation increased with an increase of the reduction time(the fractional reduction). The degradation was not observed only in the fixed bed reduction and the degradation increased with an increase of the fluidizing time after reduction by the fixed bed. It was noted that the degradation by the fluidized bed reduction was caused by the particle getting fragile by the reduction and fluidizing after the reduction.
    Moreover, a mathematical model which considered the decreases of the particle size and the particle weight in the bed was developed for the rate analysis of the fluidized bed reduction. The reduction rate calculated by the model which considered those effects agreed well with the one measured in fluidized bed and was faster than the one calculated by the model which ignored the effects.
  • A Mathematical Model for the Rate Analysis of Gaseous Reduction of Hematite Powder in a Fluidized Bed with Segregation

    pp. 823-828

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    In the case that particles of several different diameters exist in a fluidized bed, the segregation of particles is occasionally observed in the bed. Therefore, a mathematical model for the rate analysis of gaseous reduction considering the segregation in the bed was developed. The applicability of this model was confirmed by the following experiment.
    Hematite powder, which was the mixture of particles of different sizes, i.e. large particle (0.50mm in diameter) and small one (0.15mm in diameter), was reduced to magnetite in the fluidized bed (21mm in tube diameter) at 700°C by 10%CO-90%CO2 gas mixture. The gas flow rates were 4.7×10-5m3/s (STP) and 8.0×10-5m3/s (STP). The ratios of the superficial velocity, U, to the minimum fluidized velocity Umf in the case of the large particle were 1.5 and 2.8 respectively. The fluidization phenomena of the bed were observed in the cold model experiment. In the case of 8.0×10-5m3/s (STP), the bubbles were observed and the particles were fully mixed in the bed. The measured fractional reduction curve agreed well with the calculated one by the bubble assemblage model, in which it was assumed that the particle was mixed perfectly in the bed. In the case of 4.7×10-5m3/s (STP), the bubbles were not observed and the particles were not mixed in the lower part of the bed. Under this condition, the measured fractional reduction curve agreed well with the calculated one by the model considering the segregation of the particles in the bed.
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    3. A Model Design for the Charging Apparatus of a Sintering Machine Tetsu-to-Hagané Vol.82(1996), No.11
  • Flow Phenomena of Mushy Zone Caused by Suction and Formation Mechanism of V-type Segregation

    pp. 829-834

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    In order to clarify the formation mechanism of V-type segregation, flow phenomena was examined by using two kinds of samples: solid particle-water mixture and aqueous solution of NH4Cl. The former was used to simulate the slipping phenomena of equiaxed crystals in the mushy zone and the latter to simulate the remelting of mushy zone of ingot. These samples were sucked down through the outlet located at the center of the bottom of a cavity with constant velocities, which is called artificial suction. Most particles or equiaxed crystals and liquid in the upper part of the cavity moved down vertically. The V-type movement or slipping of particles were not observed. In the case of aqueous solution of NH4Cl, equiaxed crystals moved down vertically during the artificial suction and the V-type movement or slipping were not observed. However, the V-type segregation were formed in the mushy zone. It is concluded that the V-type segregation were not formed by the slipping phenomena but by the remelting.
  • Contraction of Cold Rolled Austenitic Stainless Steels Induced by Leveling

    pp. 835-840

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    Austenitic stainless steels are sometimes used for high tensile applications in cold rolled condition. However, it is difficult to manufacture sheets of those steels with good flatness, because they are rolled in high strength. Generally it is difficult to improve the flatness of a high yield strength material satisfactorily through leveling. It was found that pre-cold rolled austenitic stainless steels contract in the rolling direction through leveling. It was considered that the contraction of the sheets can be used for the improvement in flatness, although the contraction strain is small(approximately 0.1%). This study was carried out to reveal the effect of steel grades and reduction in thickness on the contraction. The experimen-tal result showed that the contraction increases as stacking fault energy increases and the amount of martensite decreases. Stress relaxation occurs simultaneously with the contraction, but the contraction strain by leveling is larger than that by stress relaxation. It is considered that the contraction is also related with Bauschinger effect.
  • Variation of Textures of TiN Deposited on (011) [100] Single Crystal of Silicon Steel due to Difference in PVD Coating Method

    pp. 841-846

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    In order to clarify the difference in the textures of TiN film due to PVD coating methods, TiN ceramic coating by HCD (Hollow Cathode Discharge) and EB (Electron Beam)+RF (Radio Frequency) methods was done on the surface of polished silicon steel samples. Pole figures of dual textures of the TiN film and related silicon steel samples were measured simultaneously using SSD (Solid State Detector) auto pole figure apparatus.
    (111)TiN pole figure of TiN film done by the HCD method showed the dominant texture of (111) [110] orientation, and (100) Si-steel pole figure of (011) [100] single crystal of silicon steel showed the dominant texture of (011) [100] orientation, in which two (220) TiN pole peaks of TiN film on TD axis were detected simultaneously, and their conjugated pole peaks manifested elliptical shape.
    In contrast, (111)TiN pole figure of TiN film done by the EB+RF method showed the weak texture of (111) crystallographic plane, and (100) Si-steel of silicon steel sheet showed the dominant texture of (011) [100] orientation, in which (220)TiN pole peaks of TiN film were detected simultaneously, and their conjugated pole peaks also manifested elliptical shape.
    It is considered that, due to the higher ionization by the HCD method than that by EB+RF, it was possible for TiN film to form the dominant texture of (111) [110] orientation, resulting in a fine and smooth TiN film with good adhesion, thereby endowing the TiN-coated silicon steel sheet with a reduced iron loss.
  • Effect of Al Content on the Amount of Solute N in Hot Rolled Coils for the Continuous Annealed Tinplate

    pp. 847-852

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    Aiming at studying the possibility to keep the solute N in hot rolled sheets low enough by the addition of high Al content instead of by low temperature slab reheating for the production of soft temper tinplate by continuous annealing from low C Al-killed steel, the effect of total Al and total N on the amount of solute N in hot rolled sheets was experimentally investigated. Main results were:
    It is possible to keep the solute N in hot rolled sheets low enough by high Al content instead of by low temperature slab reheating. For example, in the case of 40ppm of acid-soluble N and 1250°C of slab reheating temperature, Al content larger than about 0.162% can keep the solute N less than 15ppm.
    The smaller the amount of total N is, the smaller the amount of solute N in hot rolled sheets.
    A certain quantity of N would precipitate as AlN after the extraction from the reheating furnace till the end of the coil cooling during the hot rolling process, even if at the lowest coiling temperature. According to the laboratory experiment, its quantity was about 5 to 15ppm in the case of the steel with acid-soluble N=about 40ppm and with the coiling treatment at 600°C and none.
    The reason why high content of Al keeps the solute N low is considered that it increases the amount of N as AlN during slab reheating.
    The possibility is suggested to estimate the amount of total Al necessary to produce soft temper tinplate by continuous annealing for the given acid-soluble N and slab reheating temperature.
  • Time-Temperature-Precipitation Behavior of Ni-Fe Base Wrought Superalloy 706

    pp. 853-858

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    The time-temperature-precipitation (TTP) diagram is essential in the design of heat treatments for any precipitation strengthened superalloy. Some TTP diagrams have been already presented for Ni-Fe-base superalloy 706, which has been used for high temperature services. However, the γ'-γ'' co-precipitate that is the most important strengthening agent in this alloy is not seen in the literature. Moreover, effects of aluminum, titanium and niobium, important substitutional elements in γ' and γ'' precipitates, on the TTP behavior are not clear. In this study, the TTP and the time-temperature-hardness (TTH) diagrams are presented of the commercial Alloy 706 and experimental alloys containing only one or two of the key elements in a temperature range from 600 to 900°C. The alloys containing Ti were all age-hardenable, especially at temperatures between 700 and 800°C. The observation by an optical microscopy, scanning electron microscopy and transmission electron microscopy revealed the γ', γ'', γ'-γ'' co-precipitates and η precipitates in those alloys. Among the three elements, titanium plays a most important role in the precipitation strengthening behavior of Alloy 706. Furthermore, both aluminum and niobium are virtually ineffective without incorporating titanium with them. Niobium promotes the γ'' formation and suppresses the η formation. Aluminum enhances the formation of stable γ'-γ'' co-precipitates, more effectively in the co-existence of titanium and niobium.
  • Application of Local Stress Criterion Approach to Toughening Behavior due to Nickel Addition in Low Carbon Steels

    pp. 859-864

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    It is well known that nickel is one of the most effective alloy elements to improve the fracture toughness of low carbon steels. Although several mechanisms of toughening due to nickel addition were proposed, influential and persuasive mechanisms have not been established yet. In the present work, the fracture toughness of steels with nickel addition from 0 to 4 mass % were investigated for two series of steels; one for the steels subjected to the same heat treatment and the other for the steels with the same bainitic microstructure. Improvement of the fracture toughness with nickel addition was observed for the steels subjected to the same heat treatment. For the steels with same bainitic microstructure, however, the fracture toughness did not improve with nickel addition.
    The authors have previously formulated fracture toughness of low carbon steels in terms of tensile properties on the basis of the statistical local fracture criterion. They showed in the previous work that fracture toughness of the steels is expressed as a function of yield stress and cleavage fracture stress. The effect of nickel addition on fracture toughness was analyzed through the change of yield stress and cleavage fracture stress. Decrease of the temperature dependency on yield stress with nickel addition was observed for the both series of steels, indicating the tendency of toughening. Whether the fracture toughness was improved or not by nickel addition depends on the variation of the cleavage fracture stress with nickel addition.
  • Dispersion Hardening Mechanism of Y2O3 Dispersed Ferritic Steel at High Temperature

    pp. 865-869

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    The threshold stress for high temperature deformation of Oxide Dispersion Strengthened (ODS) Ferritic Steel was measured by stress abruptly loading (SAL) test at 923K and was compared with the Orowan and void-hardening stresses calculated from dispersion parameters. It was found that the threshold stress obtained by SAL test decreased from the Orowan stress to the void-hardening stress as the time elapsed under load. Therefore, it is concluded that the originating mechanism of the threshold stress comes from the Srolovitz mechanism in this steel. From these results, the origin of strength anisotropy of ODS Ferritic Steel are discussed.
  • Influence of Cold Rolling Reduction and Grain Refinement of Hot Bands on Planer Anisotropy of r-Value of Cold Rolled Extra Low Carbon Steel Sheets

    pp. 870-875

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    In this paper, a textural analysis on the planer anisotropy of r-value was carried out using extra low carbon steel sheets cold rolled at 80% and 90% with a hot band grain size of 28μm and 54μm respectively. For a detailed analysis, a model for calculating r-values from ODF-data of texture was used and the influence of each or a group of crystal orientations of the recrystallization texture in question on the planer anisotropy of r-values was studied. The following results were obtained: A development of{111}<110>{443}<110>{332}<110>{221}<110>enhanced the V-type planer anisotropy of r-values. A decrease in the intensity of these orientations by increasing the cold rolling reduction or the refinement of the hot band microstructure reduced the r-values in L and c directions and hardly affected the r-value in D direction, and as a result, the V-type planer anisotropy of r-values was improved. On the other hand, an increase in the intensity of{111}, {334}orientation by increasing the cold rolling reduction or the refinement of the hot band microstructure raised r-values in sequence of L <D<C directions and contributed to reduce the V-type planer anisotropy of r-values as a whole.
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  • Strain Rate Sensitivity of Stress-strain Curves in a Ti-Fe-O Alloy

    pp. 876-880

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    The effect of strain rate on stress-strain curves of an α-type Ti-Fe-O alloy was investigated at the strain rate between 2.8×10-5 to 2.7×10-2 s-1 at 293K. Zero strain rate curve, "Base Curve" was estimated by multiple interrupted crosshead displacement dwell test every 0.02 strain in case of the strain rates of 2.8×10-4 and 2.8×10-5. The relaxation saturated stress-strain points made a single stress-strain curve, "Base Curve". Base Curve and stress-strain curves at various strain rates were parallel. This means the stress-strain curves can be separated into strain dependent component and strain-rate dependent component. When Base Curve is fitted with Swift's equation, the stress-strain curves are interpreted as follows, σ=875.5(0.021+ε)0.176+313.3ε0.046, where σ: Stress(MPa), ε: strain and ε: strain rate.

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