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

Tetsu-to-Hagané Vol. 92 (2006), No. 6

  • Confinement of Molten Metal Using Magnetic Field

    pp. 357-363

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    In metal processing, confinement of a molten metal without mechanical contact is of great interest. For example, in a galvanizing process a sink roll, which is set in a zinc bath for changing the moving direction of steel strip, causes troubles such as deteriorating the quality of products and productivity. A new galvanizing process by using a high magnetic field which does not equip the sink roll has been proposed, where the steel strip is inserted from an inlet hole opened on the bottom of the zinc bath. Thus the stable confinement of a molten metal at the hole is crucial technical matter. The confinement of a molten metal and controlling of its flow are also essential for a cold crucible, which is indispensable for precision castings of reactive or high melting point metals like titanium and zirconium alloys. So far alternating and traveling magnetic fields have been applied for confinement of a molten metal, where unstable phenomena in hydrodynamic motion inevitably appear, so that the development of a stable confinement of a molten metal has been strongly desired. The simultaneous imposition of D.C. magnetic field and D.C. electric current is a promising method in respect of energy efficiency, however it easily generates unstable phenomena of the molten metal when a large electric current is imposed under a weak magnetic field.
    In this paper, a new method of confining a molten metal by applying D.C. magnetic field and D.C. electric current has been proposed. The usefulness of the method, which is promising in industrial applications, has been demonstrated by a model experiment using a molten metal. That is, a molten metal has been more stable confined by using plural pairs of electrodes.
  • Electromagnetic Stirring of Liquid Metal by Simultaneous Imposition of Rotating and Traveling Magnetic Fields

    pp. 364-371

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    In order to realize a higher performance of metal materials, further progress in the technology of electromagnetic stirring of liquid metal is needed, because traditional electromagnetic stirrers using rotating magnetic field (RMF) and traveling magnetic field (TMF) have several undesirable characters like severe surface deformation and weak mixing in RMF; violent surface fluctuation in TMF. In the present study, a new electromagnetic stirrer, a double axis electromagnetic stirrer (DAEMS), composed of RMF and TMF is proposed and its performance is investigated using liquid gallium. There are two modes of DAEMS, one is upward imposition of TMF and the other is downward. The former is found to give a much stronger turbulent mixing than RMF under same rotational speed, which seems advantageous to disperse CaO particles into liquid iron in the desulfurization process. The latter is found to achieve a flat and calm free surface under a rotational motion with stronger turbulent mixing than RMF. This character is thought to be advantageous to extend widely the limit of stirring due to deformation and fluctuation of free surface.
  • Effects of Alloying Elements on Solidification Structures in Cr-Mn-Ni Austenitic Stainless Steels

    pp. 372-377

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    The effects of alloying elements on solidification structures in ingots were investigated in five types of Cr-Mn-Ni austenitic stainless steels: 14%Cr-1.2%Ni-10%Mn-0.13%N, 15%Cr-4%Ni-8%Mn-0.05%N, 15%Cr-4%Ni-8%Mn-0.12%N, 17%Cr-4.5%Ni-3.5%Mn-0.3%Mo-0.10%N and 17%Cr-4%Mn-6.5%Ni-0.05%N.
    Delta-ferrite contents in ingots were increased with the increase of Cr contents and were decreased with the increase of Ni and Cu contents, and the each tendency in these alloying elements was almost equal regardless of types of steel, moreover the effect of Mo was the same as Cr. On the top of that, the relationship between Mn and delta-ferrite contents could be approximated by quadratic function. And different Mn contents in each type of steel produced different minimum delta-ferrite contents. Therefore it was obtained that the role of Mn, austenite or ferrite former, was changed by the balance between other alloying elements.
    In some steels, martensite in solidification structures increased with the decrease in Ni, Cu and Mn contents. Finally, in Cr-Mn-Ni austenitic stainless steels, the predictable equation of delta-ferrite contents in ingots, Cr and Ni equivalents were obtained by regression analysis between compositions and delta-ferrite contents.
  • Effects of Surface Oxides on the Phosphatability of the High Strength Cold Rolled Steels

    pp. 378-384

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    It is well known that Si and Mn, the basic alloying elements for steel materials, are susceptible to oxidation and form oxides on the steel surface easily, which has a great influence upon the surface performance of steel sheets such as phosphatability. In recent years, on the other hand, the cold rolled steel sheets for automobiles are required to have increasingly higher strength in order to combine improved crashworthiness and weight saving of automobiles. To increase the strength of steel sheets, the addition of these alloying elements is very effective. In this work, the kinds and the state of distribution of oxides formed on the surface of steel sheets alloyed with Si and Mn were analyzed to investigate the effects of Si and Mn upon phosphatability from the standpoint of surface oxides. It was found that phosphatability is deteriorated by the addition of Si because Si oxide films are formed on the surface of steel sheets and serve as the barriers against the reactions in phosphating treatment. It was also found that the formation of oxides is also affected by the concentration of Mn except Si and that the steel sheets excellent in phosphatability can be produced by controlling the concentration of Mn even when the concentration of Si is comparatively high.
  • Analysis of Carbide Precipitation with Alloy Element during Aging of Low Carbon Steel by Modelig

    pp. 385-392

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    Over aged samples with Mo added steel after quenching show high tensile strength than that of without Mo steel and show peculiar BH curve plotted against over aging time. To analyze these phenomena, kinetic model for carbide precipitation was derived, which deal with both cementite and cluster. The following results are obtained.
    (1) Low carbon steel with Mo, clusters are formed at room temperature after quenching. The site number used for cluster is 1015/mm3, which indicates Mo-C dipole is considerd to be the site of cluster nucleation. Clusters are dissolved with the aging temperature at 200°C in short time.
    (2) Clusters are dissolved during BH treatment (170°C ×20 min), which reduce the BH value for the sample without over aging. On the othe hand, the drop of BH with 200°C × 10 min over aging is lower, because clusters are dissolved during over aging. This causes that BH plotted against aging time shows the curve with peak.
    (3) The strength by calculation in the case of lower carbon show less value than that of higher carbon case, because cluster nucleation rate deeply depends on carbon content.
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    1. Segregation and Precipitation of Carbon in the Vicinity of Dislocations during Strain Aging in Low Carbon Steels Tetsu-to-Hagané Vol.93(2007), No.7
  • Effect of Catalyst of Iron Oxide-Carbon on Methane Hydrate Formation under Weak Stirring Condition

    pp. 393-400

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    Methane gas hydrate, MGH, has cage-like crystal structures of water molecules having a methane gas in it. Under atmospheric temperature and pressure, the amount of methane gas contained in MGH is equivalent to 172 times volume of methane gas hydrate. Many researchers are planning to develop the storage and transportation system of methane gas using MGH according to gas hydrate properties.
    The goal of this study is to develop the technology of collection and transportation of the methane gas from small-scale methane sources.
    In this study, the possibility of catalyst of iron oxide and carbon was investigated. And effect of catalyst of iron oxide, carbon and its mixture on the methane hydrate formation under weak stirring condition was studied and kinetic analysis was carried out. The acceleration effect of catalyst of iron oxide, carbon and its mixture on the hydrate formation was elucidated, when they became fine and activated by the mechanical milling.
  • Estimation of Quality Change in Domestic Steel Production Affected by Steel Scrap Exports

    pp. 401-405

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    The total crude steel production in Asian countries was 500 million t in 2004, which accounted for 47% of the total crude steel production in the world. There have been a large demand of steel scraps in Asian countries, which Japan exported 2.5 million t of steel scrap to China, 1.91 million t to Korea and 0.9 million t to Taiwan in 2003. According to our previous studies, steel scrap generation in Japan will increase until 2030. Change in steel scrap demand in Asian countries in the future will make a great influence on the amount and quality of Japan's steel scrap domestic consumption and export. In this work, estimated was the quality change in domestic steel production (Electric Arc Furnace steel for buildings & constructions) by steel scrap exports. The method based on population balance model and material pinch analysis was applied to assess the quality of domestic steel production and steel scrap consumption. The data concerning the quality (copper content) of steel scraps and recovery ratio of steel scrap from post consumer products were updated. It was found that quality requirements on steel scraps to other countries could have large influence on the quality of domestic steel.
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  • Effective Ionization for Analysis of Oxygen in Steel by Helium Glow Discharge Mass Spectrometry

    pp. 406-410

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    We developed a new He glow-discharge mass spectrometer (He/GD-MS) for ultra trace gas component analysis in iron and steels. To reconstruction of vacuum exhaust system, the turbo-molecular pump, Edwards EXT 555H, was installed on the side of the ion source chamber by modification of the electrodes for ion lens control and the mass flow controller attached to the gas introduction system. Using two standard reference materials of low alloys, we obtained the relative sensitivity factor (RSFO.Fe) of oxygen in the Fe matrix, was 0.450. The analytical results of ultra-low oxygen content of certified reference material, JSAC 0111, showed good agreement with certified value and analytical values obtained by the inert gas carrier impulse furnace fusion/infrared absorption spectrometry. The circadian fluctuation and fluctuation during the day were found to have respective accuracies within approximately 10% in RSD (%). We established a high-precision, high-sensitivity method of quantitatively analyzing an ultra-trace content of oxygen.

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