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

Tetsu-to-Hagané Vol. 83 (1997), No. 6

  • Influence of Alumina Component on Melt Formation in Sintering Process and Sinter Quality Improving Technology

    pp. 347-352

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    The bad influence of the Al2O3 component in sinter on the product yield and the sinter quality has already been verified through the experience acquired in the actual operation. It is also reported that much research has been conducted on a technology for minimizing this bad influence of the Al2O3 component in sinter.
    A method to suppress the bad influence of the Al2O3 component on the product yield and the sinter quality was examined. The purpose of this method was to form a crystal embedding Al2O3 component in a silicate slag phase, while preventing a rise in the melting point due to the Al2O3 component.
    The adoption of a method which mixes FeO raw material at a high rate in combination with the use of limestone coarser than that previously used has raised the product yield and improved the sinter quality as well. Further, with this method, a eutectic microstructure made up of "Magnetite + Fine calcium ferrite + Silicate slag" has been increased in sinter. The Al2O3 content in the eutectic microstructure is more than twice the average content of Al2O3 of the entire sinter. This condition is such that the Al2O3 component has been embedded in this eutectic microstructure. The increase in this eutectic microstructure of sinter has resulted in the improvement in the product yield and low-temperature reduction degradation index (RDI) of sinter.
  • Removal of Tin during Scrap Melting in a Converter with a Thick Layer of Slag

    pp. 353-358

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    The authors previously found that tin was concentrated in iron dust in the pilot experiments of smelting reduction with a large amount of slag. In order to apply this phenomenon to the scrap melting process, 1 kg and 5 ton scale experiments were performed to clarify the mechanism of tin removal and to improve the tin concentration into iron dust.
    It was found that tin could be removed from scrap efficiently in a scrap melting process with a thick layer of slag. In this method, a high evaporation rate of tin can be achieved by using the high temperature of hot spot with oxygen top blowing. From the experimental studies and theoretical analyses, it was supposed that most of tin vaporized as SnS. The vapor of SnS could be highly concentrated in dust by suppressing bubble burst dust. Therefore, in order to improve the tin removal ratio, it is of great importance to separate oxygen jet from metal bath to suppress bubble burst dust.
    It was also found that the tin concentration ratio remarkably increased when pulvirized coke was blasted to the hot spot. It might be possible to improve the tin concentration ratio by means of local centent of sulfur near the hot spot.
  • Evaluation of Lubrication Characteristics of Cemented Carbide Rolls for Improved Productivity in Cold Sheet Rolling

    pp. 359-364

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    The effect of roll material on lubrication characteristics is examined by using cemented carbide rolls with different carbide contents for the purpose of improving productivity in cold sheet rolling. Coefficients of friction for reduction in thickness and limit reductions of friction pick up are measured by means of the simulation testing machine of slidingrolling type. The effects of roll material and surface roughness on the coefficients of friction are quantitatively evaluated. On the other hand, the limit reductions are evaluated by both carbide area and carbide mean spacing. The results obtained are as follows; (1) The coefficient of friction is influenced more considerably by the surface topography of the roll than by the roll material. (2) The cemented carbide rolls have good anti-seizure property due to their carbide mean spacing. (3) If the cemented carbide roll should be applied to the actual mill, the maximum rolling speed would probably be two times faster than that of a 5%Cr-steel roll.
  • Life Prediction Methodology on Weatherability for Color Polyethylene Heavy Duty Coating

    pp. 365-370

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    The method for service life prediction of color polyethylene heavy duty coating has been studied from the behavior of antioxidants in polyethylene. Color polyethylene samples of 2.5 mm in thickness were exposed to the environment in Japan and Saudi Arabia for 2 years. Antioxidant concentration profiles after the exposure test were obtained by the measurement of oxidative induction time. An antioxidant consumption and diffusion model constructed in an artificial accelerated exposure test was applied to the natural environments, and the adequacy of this model was proved in the natural environment as well. The change in elongation of color polyethylene coating as a function of time in natural environmental conditions was calculated by using the model function computation and the correlation between the degradation depth and elongation of the polyethylene coating.
    This method quantitatively predicts the service life on weatherability in natural environments for color polyethylene heavy duty coating.
  • Effect of Cyclic Stressing on Delayed Fracture of High Strength Steel

    pp. 371-376

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    The delayed fracture characteristics of a PC bar steel have been examined under the FIP test. Earlier fracture occurs by applying cyclic stress compared with the constant stress even when the maximum stress is the same. The peak temperature of desorption of hydrogen at thermal desorption analysis is about 473K. Both the amount of diffusible hydrogen and desorption rate at room temperature of specimens just after the FIP test are irrelevant to the stress mode. After annealing the specimens at 473K for 30min after the test and reimmersing in the FIP solution, the total amount of diffusible hydrogen decreases to about 2/3. The effect of cyclic stressing appeares as the increase in the reduction of hydrogen released up to 473K. It is discussed that the effect of cyclic stressing on the delayed fracture characteristics is through a dynamical interaction of hydrogen with defects produced by plastic deformation.
  • Effects of Composition and Microstructure of Hydrated Chromium Oxide on Adhesive Property of PET/I Film Laminated TFS

    pp. 377-382

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    The surfaces of tinplate and tin free steel (TFS) are traditionally coated with lacquers for applications to can stock. Recently, replacement of lacquers with thermosetting resins, films of thermoplastic resins have been attempted to can ends, drawn cans, stretch-drawn cans, 18 liter cans, aerosol parts and other containers. These laminated materials for can containers fundamentally require formability, corrosion resistance and adhesive property with polyethylene terephthalate/isophthalate co-polimerized (PET/I) film.
    The typical laminated material consists of the bottom layer of metallic chromium, middle layer of hydrated chromium oxide and surface layer of PET/ I film (12 to 25 micrometers thick) on steel substrates. A base steel, TFS, was prepared by cathodic electrolysis in a chromic acid (CrO3) solution containing either a fluoride compound or a sulfuric acid. A proper quantity of hydrated chromium oxide is necessary for sufficient adhesion, depending on its composition and microstructure. Laminated TFS with about 100mg/m2 metallic chromium and about 5 to 20mg/m2 hydrated chromium oxide satisfies the adhesivity.
  • Formation and Falling Mechanism of Black Oxide Layers in High Speed Steel Rolls during Hot Strip Milling

    pp. 383-388

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    To shorten the roll transfer time and improve the surface quality of the hot-rolled products, the black oxide layers formed on the roll surface were analyzed by means of SEM, WDS and X-ray diffraction techniques, for two rolls with different W and Mo contents. The observation of the near-surface region of the HSS roll with more W and Mo additions indicated that microcracks formed in the black oxide layers on the roll surface, and easily propagated along needle-shaped M2C type primary carbides segregated in the intercellular regions. This led to further crack growth along M2C carbides, and then to the final falling of the black oxide layers from the roll surface. On the other hand, in the HSS roll with less W and Mo additions, the black oxide layers were hardly evident, since they were fallen off easily from the roll surface. These results were interpreted by the molybdenum addition which affected the amount of M2C carbides and the black oxide formation, suggesting the existence of a proper molybdenum content to achieve the stable black oxide layers on the HSS roll surface.
  • Enhancement of Shape Memory and Its Anisotropy by Training Treatment in an Fe-32Mn-6Si Alloy

    pp. 389-394

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    The improvement of shape memory effect due to the austenite (γ)_??_epsilon (ε) martensitic transformations and the development of its anisotropy by training treatment were studied by using an Fe-32Mn-6Si alloy. The training treatment of five times repetitions of 2% tensile deformation at 300K and heating up to 723K was given to the solution-treated samples. By this treatment, lots of stacking faults are introduced in the samples. The test specimens were cut from the trained plates either parallel (0°sample) or vertical (90°one) with respect to the training direction.
    In the 0° samples the pre-existing stacking faults are found to be very effective not only to produce the stress-induced ε martensite but also to increase the γ strength against usual slip. A seemingly one thick ε plate has been revealed to consist of nano-scale γ/ε lamellar structure which is preferable to hold the back stress. The shape recovery improved due to the reversible motion of Shockley is partial dislocations assisted by this back stress. The recovery stress for backward motion of Shockley partial dislocations during the ε→γ reversion is found to increase markedly by the training treatment.
    On the other hand, in the 90°samples, the pre-existing stacking faults are of no use to enhance the stress-induced εmartensitic transformation and they rather hinder the transformation. Intersections of ε/ε plates and/or ε plates/stacking faults were frequently observed. Since the γ is almost equally strengthened in the 0° and 90°samples by the training, the slight increase in the shape recovery strains in the 90°samples compared with the non-treated samples is presumably resulted from the existence of higher back stress.
  • Influence of Microstructures on Fatigue Crack Initiation and Propagation in Low-carbon Steel

    pp. 395-400

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    The influence of microstructures on fatigue crack initiation and threshold behavior of crack growth in large fatigue crack was investigated using notched specimens and CT specimens. Three different microstructure of low carbon steels simulated heat affected zone of welds were prepared. The crack initiation behavior for each materials were also discussed from fractographic examination and in situ observation tests in SEM with notched fatigue spesimens. Bainitic microstructures showed higher threshold stress intensity factor renge for fatigue crack growth than ferritic microstructure. The difference in threshold level between microstructures tested would be mainly resulted from the crack closure, but the influence of microstructures on large fatigue crack growth could not be described only in terms of crack closure mechanism. On the other hand, the small crack region which occupied the most of fatigue life was affected by microstructures. Particularly, the effects of microstructure on the shape and growth of Stage I fatigue crack. The Stage I fatigue crack size is almost correspondent with the microstructural unit size, i.e grain size or lath packet size.
  • Influence of Microstructures on Non-propagating Behavior of Fatigue Crack in Notched Specimens of Low-carbon Steel

    pp. 401-406

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    The influence of microstructure on non-propagating behavior of fatigue crack below the fatigue limit was investigated using low carbon steels with three different microstructures simulated heat affected zone of welds. Notched round bar specimens with different stress concentration factors were fatigued under axial loading at the stress ratios R=-1 (tension-compression). Fractographic and metallographic observations of non-propagating cracks at the stress level below fatigue limit were examined, and correlation between non-propagating crack and microstructures was investigated. Non-propagating cracks could be classified as Stage I or Stage II, depending on the microstructure and notch root radius. In the case of dull-notched specimens, where the notch factor in fatigue is proportional to stress concentration factor, the non-propagating crack is Stage I type regardless the microstructure, although Stage II type cracks were observed in sharp notched specimens for particular materials. The criteria for both Stage I and Stage II type non-propagating crack were discussed on the basis of the point stress model and fracture mechanics.
  • Analysis of Recycle System of Material with Decrease in Stock Growth Rate and Its Application to Steel

    pp. 407-412

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    Recycling of various materials has been urged worldwide for environmental reasons. Promotion of recycling is expected to reduce the environmental pollution caused by material production. However, recycling of materials leads to increase in concentration of impurities in the material, which usually lowers social utility of the use of the material. Therefore, establishment of analyzing methods of the whole recycling system is needed to evaluate the effect of recycling totally.
    In this study, we proposed an analytical model for recycling system and developed formulas for the comprehensive evaluation of recycling system, assuming that the stock of materials in our society will continue to increase but will converge to a certain level.
    Our proposed method can be used for forecast and evaluation of material production, recycling ratio, concentration of impurities, environmental load, etc.
    By applying this model to iron and steel materials, quantitative trade-off relation between the improvement of environment and deterioration of the quality by copper accumulation was made clear.

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