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

Tetsu-to-Hagané Vol. 87 (2001), No. 3

  • Electromagnetic Migration Force Acting on Two Non-conducting Particles in DC Electromagnetic Force Field

    pp. 113-120

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    Interaction between two non-conducting particles in DC electromagnetic field was studied by numerical analysis. Experiments were conducted on the particle behavior using an electrolytic cell, and compared with the calculated results. In the calculation, distributions of electric field, current, electromagnetic force and pressure field were obtained for the single particle case and for the three different configurations of two particles, in which the cascading directions of two particles are parallel to the directions of electric current (case 1), magnetic field (case 2) and electromagnetic force (case 3). Exerting electromagnetic forces on the particles were calculated by integration of the pressure on the surface area.
    Interaction forces between the two particles were shown to be absent, namely, neither attractive nor repulsive in all the cases. However, the magnitude of the electromagnetic forces exerting on the particles (Gc) differed with the configuration of two particles. As the interparticle distances decreased, Gc of case 2 became less than that of single sphere, however, Gc became lager in the case 1 and case 3. This tendency agreed with the model experiments, qualitatively.
  • Development of a System to Diagnose and Prevent Internal Cracks in Continuous Casting Taking Account of the Effect of Compression Casting

    pp. 121-128

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    A diagnostic system to prevent internal cracks in slab continuous casting was developed which takes accout of the effect of compressive strain by compression casting (CPC). The deformation strain of solidifying shell during continuous casting was calculated by the total strain model, which is composed of unbending strain term, bulging strain term, misalignment strain term and compression casting strain term. Dimple-mark roll test and intentional misalignment of rolls revealed that the proposed strain model could predict the occurrence of internal cracks incorporated with the critical strain model for internal cracking reported by Nagata et al. These results lead to the on-line internal crack diagnostic system which enables the stable operation of the continuous caster at high speed under soft cooling.
  • Determination of Trace Silicon in High Purity Aluminium by Molybdosilicic Acid Blue Spectrophotometry after Fluoride Separation

    pp. 129-131

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    The amount of impurity silicon in high-purity aluminium is far below the detection limit of the JIS analytical method. So, the possibility of the determination by molybdosilicic acid blue spectrophotometry after fluoride separation has been studied. Although the presence of matrix aluminium disturbs the quantitative formation of the silicon tetrafluoride to be analyzed, the optimization of analytical conditions such as concentration and amount of hydrofluoric acid enables the determination of sub-ppm level silicon with the detection limit of 0.17 ppm.
  • High-temperature Oxidation of a Ti-15V-3Cr-3Sn-3Al Alloy in CO2 Atmosphere

    pp. 132-137

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    The oxidation of a Ti-15V-3Cr-3Sn-3Al alloy has been investigated in the temperature range of 1000K to 1400K in CO2 atmosphere. The results of optical microscopy, electron probe microanalyses and powder X-ray diffraction measurements on the oxide scales formed during oxidation indicate that the scales consist of an external and an internal scale. The oxide phases and the carbide phase formed at 11001300K are identified as tetragonal-TiO2, orthorhombic-TiO2, α-Al2O3, V2O5 and TiC. The oxides formed at 1400K are identified as SnO2, together with the oxides and the carbide described above. The parabolic rate laws were confirmed on the growth of the internal scale layer and the permeation depth of oxygen in the alloy with the apparent activation energies, 210 kJ/mol and 166 kJ/mol, respectively.
  • Reaction between Solid Iron and Molten Zinc Containing Aluminium

    pp. 138-145

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    Ti interstitial free steel specimens with grain size of 50 μm in diameter polished with buffs were immersed in molten Zn containing 0.1-1.0 mass% Al for 4 to 3600 s at 733K. Formation and growth kinetics of Fe-Zn and Fe-Al alloy layers was examined metallographically. A fragmentary δ1(f.δ1) layer composed of small discrete δ1 phase particles embedded in a matrix of η phase was formed on the surface of the specimen in molten Zn containing 0.1 mass% Al and its thickness increased with immersion time according to a linear rate law. In molten Zn containing more than 0.3 mass% Al, a very thin layer composed of small Fe2Al5 crystals was formed on the specimen surface, and then another type of small Fe2Al5 particles in the shape of lens were formed between the Fe2Al5 crystal layer and the specimen. The Fe2Al5 crystal layer disappeared, as the lens-like particles of Fe2Al5 phase developed to a layer, the thickness of which increased with immersion time according to a parabolic rate law that means the layer growth is controlled by diffusion. In molten Zn containing 0.15-0.25 mass% Al, f. δ1 phase was formed between the crystal or diffusion layer of Fe2Al5 phase and the specimen. It appears that the formation of f. δ1 phase is caused by penetration of the molten Zn through cracks of the Fe2Al5 layer.
  • Stretch-flangeability of High Strength Hot Rolled Steel Sheets with Bainitic-ferrite Microstructure

    pp. 146-151

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    Recently, high strength hot rolled steel sheets have been applied to mainly chassises and wheels and high formability, especially high stretch-flangeability is required on those parts. Bainitic-ferrite single phase microstructure has been proposed to obtain the high stretch-flange formability. In this paper, the effects of metallurgical factors of bainitic-ferrite single phase microstructure on stretch-flangeability is studied.
    The effects of atomic ratio of Ti by C of the bainitic ferrite steel and the void creation morphology of bainitic-ferrite, bainite and ferrite-pearlite steel after stretch flange formation are investigated. The bainitic-ferrite steels with access of 1.0 atomic ratio of Ti by C shows highest stretch-flangeability among the studied steels because cementite is not existed.
    Cemmentite existed in baintic-ferrite steels with 0.5 atomic ratio of Ti by C, bainite and ferrite-pearlite steels, causes the void initiation during stretch flange formation. In addition of above mentioned, the stretch-flangeability is deteriorated by TiC precipitate and increase grain size.
  • Delayed Fracture Resistance of 1500 MPa Grade Bolts Influenced by Galvanic Corrosion

    pp. 152-157

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    Delayed fracture resistance of 1500 MPa grade bolts was investigated taking account of hydrogen absorption due to galvanic corrosion. 1500 MPa grade bolts with various chemical compositions were served for accelerated delayed fracture test under the given clamp conditions. Delayed fracture resistance of the bolts appeared to be improved with increase in their K1scc values. However, 1500 MPa grade maraging type steel bolts were delayed fractured although it had extremely high K1scc value. In order to estimate hydrogen amount absorbed into the testing bolts due to galvanic corrosion, Thermal Desorption Spectrometry (TDS) analysis was conducted. It was revealed that maraging type steel touched with a mild steel absorbed large amount of diffusive hydrogen owing to galvanic corrosion. The relationship between delayed fracture resistance of 1500 MPa grade bolts and their K1scc values was discussed from the viewpoint of galvanic corrosion.

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