Zairyo-to-Kankyo
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ONLINE ISSN: 1881-9664
PRINT ISSN: 0917-0480

Zairyo-to-Kankyo Vol. 40 (1991), No. 7

  • Evaluation of Hydrogen Embrittlement Type SCC in Duplex Stainless Steel Welded Joint and It's Mechanism

    pp. 461-469

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    The HESCC initiation time was predicted by numerical analysis method. In the analysis, the HESCC initiation condition was determined by the correlation between hydrostatic stress and hydrogen activity in ferritic phase near the tip of austenitic phase on specimen surface. It was confirmed that the criterion for HESCC initiation could be defined in low yield strength steel such as duplex stainless steels as same as high strength steels. In addition to that, the mechanism for HESCC in duplex stainless steels and its welded joints was studied by fractographic observation with facet pit method. As the results, it was found that ferritic phase fractured in quasi-cleavage mode and austenitic phase in ductile mode. From the morphologies of facet pits formed on ferritic phase, it was clarified that the fracture planes in ferritic phases were mainly constituted of {100} plane in lower stress intensity region, and {110}, {112} plane in higher one. Consequently, the mechanisms for HESCC in duplex stainless steels contained lattice decohesion at lower stress intensity and fracture on slip plane at high stress intensity. From the view point of mechanism for HESCC, it was clear that the criterion for HESCC initiation mentioned above is also applicable for a fracture under the low stress intensity region.
  • Corrosion Resistance of Hot-dipped Zn-Al Alloy Coatings in Coastal Areas

    pp. 470-477

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    To estimate the corrosion resistance of hot-dipped Zn-Al alloy coatings used for protective coatings for outdoors telecommunications plants in coastal areas, the corrosion behaviour of Zn-Al coatings containing 0.2 to 30wt% aluminum was investigated by polarization measurements in NaCl solution and salt spray testing.
    The results are summarized as follows:
    a) Corrosion potential of Zn-Al coatings of any aluminum content were almost the same as that of pure zinc in a 3% NaCl solution. This indicate that Zn-Al coatings of any aluminum content can be expected to provide the same galvanic protection to a steel substrate as a pure zinc coating.
    b) The polarization curves for Zn-Al coatings in the NaCl solution were also the same as that of pure zinc coatings.
    c) The polarization curves of Zn-Al coatings with crevices were almost the same as that of non-creviced specimens, despite the accelerated anodic polarization current of creviced specimens of pure aluminum coating, whose crevice corrosion in coastal areas is well known. Consequently, the crevice corrosion of Zn-Al coatings need not be considered.
    d) The weight loss of Zn-Al coatings in the salt spray testing was reduced in proportion to increasing aluminum content.
    e) The corrosion products of Zn-Al coatings after salt spray testing consisted mainly of ZnCl2·4Zn (OH)2.
  • Microkinetics of Hydrogen Assisted Cracking by Inversion Processing of Elastic Waves Utilizing Theoretical Green's Function

    pp. 478-486

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    In order to elucidate the microkinetics of hydrogen assisted cracking of alloys, new AE source inversion processing utilizing theoretical Green's function was proposed. In this processing, surface displacement detected by a displacement sensor was deconvoluted by the theoretical Green's function for dipole source, and the energy released by crack formation was obtained. This processing, however, becomes possible when some special conditions were satisfied, so detail experiments on sensor calibration, radiation pattern of longitudinal wave (P-wave), wave distortion by reflected P-wave, were done using three channel AE data acquisition system (ADAS) developed by us. It was found that about half of the detected waves during hydrogen assisted cracking were generated by the the Mode-I type microcracks, and could be inversion processed by the proposed method. Another half were found to be the waves emanated by mixed mode cracking. Source waves suggest that new surface with diameter of few ten micrometers are created with time of 1 to 5 microsecond. Intergranular cracks in the MnS segregated zone sandwiched by dimple fracture in the front of macroscopic crack tip where the highest hydrostatic pressure exists might correspond to the source waves obtained by this method. The number of AE waves and these intergranular cracks agreed well.
  • Study on Materials for Anaerobic Bioreactor

    pp. 487-490

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    The selection of materials for an anaerobic bioreactor is one of the most important issues in design. But, so far no sufficient study has been made yet on this subject. This report presents the findings from the experiments the authors carried out on such materials as various types of metals and concretes for possible use in an anaerobic bioreactor. In the experiments, materials were tested with high-concentration wastewater from kraft pulp mill in a thermophilic, anaerobic digestio n vessel. The system used consisted of pretreatment equipment, an anaerobic bioreactor for methane fermentation, a membrane module unit and a gas treatment system.
    The experiment revealed that: 1) stainless steels and alminum had a good corrosion resistance, but cast iron (FC 20) showed less corrosion resistance and 2) silica fume mixed concrete indicate a good corrosion resistance.
  • Degradation of High-Temperature Oxide Superconductors

    pp. 491-497

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    High-temperature oxide superconductor YBa2Cu3Oy reacts with water in moisture producing nonsuperconducting materials, such as BaCO3, Y2BaCuO5, CuO. As a result, the superconductivity of the YBa2Cu3Oy is degraded. In this article, the studies of the degradation of Y, Bi, Tl-based superconductors by the methods of resistive transition, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope are summarized. In addition, several attempts to prevent the degradation in moisture, such as coating, are summarized.
  • Fractal Character of Fracture Surfaces on Metals

    pp. 498-505

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    In this review, the fractals in the fractography is described, using brittle fracture surfaces of chromium and molybdenum, and stress corrosion cracking surfaces of SNCM 439 steel. It is emphasized that the quantitative fractography at the atomic region is opened, combining scanning tunneling microscopy with fractal geometry.
  • Corrosion of Copper Tubing in Hot Water Supply Systems

    pp. 506-507

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