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

Tetsu-to-Hagané Vol. 91 (2005), No. 6

  • Future Developments of the In-Rotating-Liquid Spinning Process

    pp. 511-520

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    Future developments of the In-Rotating-Liquid Spinning Process (INROLISP) was discussed with reviewing past results. Following countermeasures will be necessary to come into wide use but their order of priority shifts according to each purpose: 1) using a melting process to prevent melt from contamination (ex. the cold crucible melting), 2) improving the inner surface in the nozzle (ex. metal-oxide liner on metalbase), 3) controlling the oxide skin on the jet, 4) lowering density and adjusting the cooling ability in the coolant, 5) analyzing and controlling for solidification morphology under the boundary-layer separation between jet and coolant, 6) raising the observation technique of the jet, 7) speedy taking as-spun wires out of the drum. The INROLISP should not be expected to become all-round process but should be variously modified to be suitable for each purpose. As an example the spinning in gas process, which can make unidirectional solidification, was proposed. In the course of developing, it is important not to lose what merit is expected in the spinning process.
  • Rapid Reduction of Fine Iron Ore Transported with CH4 Gas

    pp. 521-527

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    Acceleration of reduction rate and decrease of reaction temperature in ironmaking process are key issues to reduce the CO2 emission and the energy consumption. To solve the problem, effective use of H2 gas or CH4 gas including both reducing agent of carbon and hydrogen is proposed. Therefore, a laboratory scale fine iron are particles-gas conveyed system was utilized to measure the reduction rates of fine are by using H2 and CH4 gas at high temperature. H2-N2 and CH4-N2 mixture having various flow rates and compositions were flowed downward with fine iron are through a cylindrical reactor maintained at a constant temperature of 1373 to 1723K.
    The reduction process was found to proceed in such manner that the iron are particles were reduced topochemically under the condition of 1573K. The reduction rate in CH4 gas became larger than that in H2 gas with increase in the temperature, because of the contribution of carbon deposited on the surface of iron are particle. Fractional reduction of ore in CH4 gas reached over 0.8 at 1573K in 1 s. In the reaction rate analysis, it was concluded that the major fraction of overall reaction resistance was attributable to chemical reaction between the iron oxide and the carbon dissolved in metallic iron. The activation energy in CH4 reduction was evaluated to be 192.5kJ/mol and it was almost same as that in decomposition of CH4.
  • Hot Metal Dephosphorization Behavior by Sintered Dephosphorization Agent Contain Al2O3

    pp. 528-536

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    In order to enhance the slag formation and the hot metal dephosphorization, a behavior of reaction using a sintered agent containing Al2O3 has been investigated. A new reaction model based on the coupled reaction model considering not only the rate of mass transfer and chemical reaction but also the rate of slag formation has been developed. The rate of dephosphorization was improved and phosphorous content in the hot metal was lowered in shorter treatment time by the sintered dephosphorization agent containing Al2O3 due to the enhanced slag formation. The reaction model described the behavior of dephosphorization reaction well in both cases using sintered and non-sintered dephosphorization agents.
  • The Development of Internal Defects Evaluation Method in Continuous Casting Slabs by High Frequency Supersonic Flaw Detection Technique

    pp. 537-545

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    We developed the internal defects and inclusions evaluation method in continuous casting cleanliness slabs by using supersonic flaw detection technique.
    The size and position of defect in a slab was detected by several echoes of supersonic by a neural network signal treatment. Internal defect and inclusion was distinguished according to the phase and amplitude of the echoes. The size of defects was calibrated by preliminary artificial defect testing. Those results was compared with the optical microscope observation of the defects which revealed by polishing at 0.1 mm interval.
    The results were follows.
    (1) Whole pinhole type defects detected by the present method agreed with that by the optical microscope observation. And the 90 percent of inclusion type defects by this method agreed with that by the optical microscope observation. This result suggested that this method was enough precision for practical use.
    (2) On the other hand, some kinds of flaw such as Al2O3 cluster and pin hole could not be distinguished by this neural network treatment.
    (3) The different shape of pinhole type defects and the cluster type inclusions could be classified with a slope α which was obtained by size distribution fitting of doubly exponential function.
  • Water-model Experiments on Gas and Liquid Flow in the Continuous Casting Immersion Nozzle

    pp. 546-552

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    Water-model experiments were carried out to understand the behavior of argon gas introduced into the immersion nozzle from the vicinity of the sliding gate.
    The gas was completely lifted up into the tundish when the water flow rate was lower than a certain critical value. On the other hand, it was completely carried deep into the mold when the water flow rate was higher than another critical value.
    An estimation method of the two critical values was proposed.
    The mean diameter of bubbles for a water flow rate between the two critical values increased with an increase in the distance from the sliding gate. The relationship between the mean diameter and the characteristics of water flow in the nozzle was revealed.
  • Finite Element Analysis of Forming Limit of High-strength Steel Sheets Using Ductile Fracture Criterion

    pp. 553-559

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    In this study, first, the limit strains of a few types of high-strength steel sheets under various strain paths from balanced biaxial stretching to uniaxial tension are examined by the Marciniak-type in-plane biaxial stretching test. They are compared with those derived from some criteria for ductile fracture. It is found that the fracture strains derived from the criterion proposed by Cockcroft and Latham give the best fit to the experimental results. Next, as fundamental 3-dimensional press forming processes, the square cup deep drawing and the T-shape forming of the high-strength steel sheet are analyzed by the finite element method combined with the ductile fracture criterion. The dynamic explicit finite element program LS-DYNA ver. 970 with membrane shell is used. The comparison with the experimental results demonstrates that the fracture initiation sites and the critical punch strokes are successfully predicted by the present approach.
  • Influence of Phosphorus, Sulpher and Oxygen on 65% Nitric Acid Corrosion Resistance of Super High-clean SUS316L Stainless Steel

    pp. 560-566

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    For the purpose to verify the effect of decreasing phosphorus on corrosion properties of stainless steels, corrosion resistant tests in 65% nitric acid solutions were carried out for super-low phosphorus content SUS316L type stainless steels which were manufactured by cold crucible type levitation melting method using Ca-CaF2 flux for aiming at the dephosphorization. By decreasing phosphorus content in these steels from 0.026 to 0.0002 mass%, the corrosion rate in 65% nitric acid solutions decreased remarkably. Especially even under 0.001% phosphorus content, this decreasing phenomenon could be observed. Thus extreme dephosphorization improves the corrosion resistance of stainless steels marvelously.
    As for the non-metallic tramp elements, there were linear relations between corrosion rate and the very small amount of sulfur and oxygen contents in the super-low phosphorus stainless steels containing under 0.0002 mass% phosphorus. So the super high purification of these elements is also very effective for the improvement of corrosion resistance against nitric acid solutions.
    It is known that the corrosion of austenitic stainless steels containing over 0.003 mass% phosphorus in nitric acid solutions is intergranular corrosion. In the present work, it is confirmed that the corrosion of super-low phosphorus content SUS316L type stainless steels even at 0.0002 mass% is not uniform corrosion but intergranular corrosion.
  • Microstructural Change near Retained Austenite Interface during the Formation Process of White Etching Area under Rolling-slip Contact

    pp. 567-573

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    The microstructural change near interface between retained austenite and martensite during the formation process of White Etching Area (WEA) under rolling contact is investigated to characterize formation mechanism of WEA using the disk on roller type rolling contact fatigue equipment. These examinations were carried out under rolling/slip contact. When the slip ratio between a roller and a disk is 14%, acicular structure and WEA have been formed below the contact area. The sample has been investigated using Optical Microscope (OM), Scanning Ion Microscope (SIM), Transmission Electron Microscope (TEM) and X-ray diffraction equipment.
    It is found that acicular structures have been formed before an appearance of WEA. It is considered that acicular structures are formed by shear deformation of martensites. These are at angles of 30° or 160° with rolling contact surface. These angles have been suggested a direction of shear stress that acts on material under this experimental condition. In this microstructural change process, volume fraction of retained austenite has been decreased after the formation of acicular structures. The microstructural change of retained austenite occurs under different contact stress 4.2 GPa and 3.3 GPa, though hardness of both specimens is not change. Volume fraction of retained austenite under WEA formation process decreases with rolling contact time.
    In this microstructural change process, many voids have been formed near the interface between retained austenite and martensite. This is suggested that the interface acts as voids formation points in the formation process of WEA under rolling/slip contact.

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