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

Tetsu-to-Hagané Vol. 92 (2006), No. 2

  • Magnetohydrodynamic Calculation Method for Electromagnetic Sensor

    pp. 53-57

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    A new type of magnetohydrodynamic calculation method is proposed to evaluate the electromagnetic sensing process, in which fluid dynamics makes much influence on the electromagnetic field. First, multi-phase flow of molten steel and slag are momentarily performed in fluid calculation in the proposed method. Second, conditions of multi-phase flow are momentarily performed in electromagnetic calculation. Last, secondary voltages are momentarily calculated. It is able to observe internal state of multi-phase flow of molten steel and slag by fluid calculation. It was able to understand the relation between slag detection process and sensor output by magnetohydrodynamic calculation.
  • Improvement of Sensitivity to Delayed Fracture from Pitting Corrosion of Spring Steels for Automobile by Alloying

    pp. 58-67

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    In order to strengthen the spring steels of suspension for automobile, it is necessary to reduce sensitivity to delayed fracture caused by the hydrogen from corrosion environment. In this research, influence of the pitting corrosion resistance on the sensitivity to delayed fracture caused by wet-dry cyclic corrosion in 5 mass% NaCl solution at 308K, was investigated with SSRT test, thermal hydrogen analysis and silver decoration method. The results of this research are as follows.
    (1) The spring steel containing Ni, Mo and small quantity of B has superior pitting corrosion resistance (V'cq100) to the spring steel containing Ni and Mo.
    (2) Normalized maximum load and time to failure calculated from SSRT test results representing the sensitivity to delayed fracture, were improved as the V'cq100 was increased with addition of the effective alloying elements.
    (3) The thermal hydrogen analysis to the test piece with rust and without rust showed the unique hydrogen peak between 673K and 773K.
    (4) It was found the hydrogen of this peak was the hydrogen generated and condensed at rust/steel interface during corrosion reaction, by the silver decoration method.
    (5) The normalized time to failure was decreased with increasing of the condensed hydrogen at the rust/steel interface.
    (6) It was concluded the enhancement of V'eq100 by addition of the effective alloying elements, was effective to reduce the sensitivity to delayed fracture of the high strength spring steel through decreasing of the hydrogen generated in the wet-dry cyclic corrosion reaction.
  • Localized Dissolution of Zn-Al Alloy Coated Steel in Neutral Solution with Cl- by Photon Rupture Method

    pp. 68-74

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    A photon rupture method, film removal by a focused one pulse of pulsed Nd-YAG laser beam irradiation, has been applied to investigate initial stage of localized dissolution of Zn and Zn-Al alloy coated steels, which were formed nitrocellulose films as a protective film, in 0. 5kmol m-3 H3BO3-0. 05kmol m-3 Na2B4O7 (pH=7. 4) with 0. 01kmol m-3 chloride ions. This method can remove oxide films and nitrocellulose films on coated layer by laser ablation without any contamination from film removing tools, and the removing speed is extremely high. At low applied potentials, all samples reformed oxide film after films were removed by this method. The oxide film formation kinetics follows on inverse logarithmic law in agreement with Cabrera-Mott theory. However, as increasing applied potential, after some period, localized dissolution occur at nitrocellulose films were removed area. The peak currents of Zn-5mass%Al coated steel specimens were larger than those of Zn and Zn-5mass%Al coated specimens. This result suggest that high aluminum containing coated layer does not show good corro-sion resistance in frequently oxide film removal environments.
  • Effects of V, Nb and Ti on Creep Property and Toughness of Weld Metals for High Cr Ferritic Heat Resisting Steels

    pp. 75-82

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    The effects of V, Nb and Ti on the creep property and the toughness of weld metals for high Cr ferritic heat resisting steels were investigated. The following were clarified:
    (1) Increasing V from 0mass% to 0.11mass% improves the creep property and impairs the toughness. Increasing V by more than 0.11mass% impairs the creep property and improves the toughness.
    (2) The creep property is improved and the toughness is impaired by adding a small amount of Ti.
    (3) Addition of Nb improves the creep property and impairs the toughness. However it improves the balance between the creep property and toughness more than the addition of V and Ti.
    (4) The changes of the properties due to V, Nb and Ti could be explained by changes in the morphology of MX.
    (5) The changes in morphology of MX could be explained by changes of driving force and grain growth kinetics.
  • Hydrogen Embrittlement Properties of Ultra High-strength Low Alloy TRIP-aided Steels with Bainitic Ferrite Matrix

    pp. 83-89

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    Hydrogen absorption behavior and hydrogen embrittlement properties of 1000-1800 MPa grade ultra high-strength low alloy TRIP-aided steels with bainitic ferrite matrix were investigated. The TRIP-aided steels absorbed a large amount of hydrogen, compared with the conventional tempered martensitic and bainitic steels. It was expected that the absorbed hydrogen was principally trapped in interlath retained austenite films and along bainitic ferrite lath boundary. Superior hydrogen embrittlement performances such as low hydrogen embrittlement susceptibility and high delayed fracture strength were achieved in the TRIP-aided steel. This may be associated with hydrogen trapping effect and TRIP effect of retained austenite.
  • Effects of Nitrogen on the Mechanical Propeties of 316LN Stainless Steels

    pp. 90-96

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    Type 316LN stainless steel is one of the candidate structural materials for the low stress regions of the toroidal field coil for International Thermonuclear Experimental Reactor (ITER). It was confirmed that contribution of nitrogen to 0.2% yield strength of 316LN at 4K is more than that of carbon in a previous paper. 8) However, it has never be investigated the tensile property of the 316LN, in which carbon content was controlled at low level and nitrogen content was varied. Therefore, it was systematically investigated the mechanical properties of the low carbon controlled 316LN, in which nitrogen content was varied in the wide range, at 4K, 77K, room temperature and high forging ternperatures. In consequence, it was confirmed that the cryogenic elongation of the specimens included the high nitrogen content over 0.221mass% was lower than an elongation-(T-Md30) curve. T means tensile test temperature. In addition, the data of the reduction of area at 1373K were increased with increasing nitrogen content over 0.175mass%. It was inferred that these behaviors were influenced by enhance ment of dislocation density by super saturation of solution nitrogen.
  • Creep Life Evaluation Based on Hardness Method of High-Cr Ferritic Steels

    pp. 97-104

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    The softening caused by long-term aging for 10Cr-1.5Mo-VNbN steel was investigated with hardness test at temperature range of 500 to 650°C up to 105 hours. The softening caused by creep was also investigated at temperature range of 600 to 650°C under stress of 98 to 294 MPa. The change in hardness during long-term aging was able to be expressed by a simple curve in plotting against Larson-Miller parameter. The Softening was accelerated by the stress larger than 79 MPa. The change in hardness during creep under the stress of σ (MPa) was correlated with those of long-term aging by plotting against the parameter of logT+log(20+logt)+0.000239(σ-79)
    where T is the test temperature (K) and t is the loading time or aging time (h).
    A method to detect the creep damage and to estimate the residual life was deduced from the above mentioned results.

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