Journal of the Japan Institute of Metals and Materials
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
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Volume 79, Issue 7
Displaying 1-6 of 6 articles from this issue
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Overview
  • Crystallographic Restriction in Martensite and Bainite Transformations in Steels
    Goro Miyamoto, Takeshi Kaneshita, Tadachika Chiba, Tadashi Furuhara
    2015 Volume 79 Issue 7 Pages 339-347
    Published: 2015
    Released on J-STAGE: July 01, 2015
    DOIhttps://doi.org/10.2320/jinstmet.J2015017
    JOURNAL FREE ACCESS
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      Attention to lath martensite and bainite in steels has been increasing due to their good mechanimcal properties. Various boundaries bewteen K-S variants contained in those microstructures contribute to their high strength and toughness so that deeper understand of nature of those boundaries is required. EBSD analyses have revealed that different variant grouping tendencies appear depending on composition and transformation temperature, such as variants belonging to the same Bain group, variants sharing the same close-packed plane parallel relationship. Kinematical compatibility (KC) condition can explain variant pairs coupled preferentially in lenticular and thin plate martensite satisfactory. In addition, it is revealed that some of the variant pairs observed in lath martensite and bainite are favorable for the KC condition when double shears are assuemd for lattice invariant shear.
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Regular Article
  • Creep Rupture Strength for Weld Joint of 23Cr-45Ni-7W Alloy
    Kyohei Nomura, Keiji Kubushiro, Hirokatsu Nakagawa, Yoshinori Murata
    2015 Volume 79 Issue 7 Pages 348-355
    Published: 2015
    Released on J-STAGE: July 01, 2015
    DOIhttps://doi.org/10.2320/jinstmet.J2015015
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      The creep rupture strength and the degradation mechanism of 23Cr-43Ni-7W alloy weld joints were investigated by creep rupture tests and microstructure observation of the ruptured specimens. The creep rupture tests were conducted at 973, 1023, and 1073 K at stresses from 80 to 180 MPa. The creep strength of the weld joints was higher than that of the base metal. The ruptured area of every specimen was over 10 mm away from the bond line. The microcracks increased gradually up to 10 mm from the bond line, above which they increased suddenly. In the grains, traces of M23C6 were observed near the bond line, and the sizes of the M23C6 deposits increased further away from the bond line. But the size of the Laves phase was constant in every observed area. On the grain boundary, the grain boundary shielding ratio by precipitates was constant until 10 mm from the bond line, above which it decreased. These observations show that the creep strength near the bond line is higher than that of the base metal because of both precipitation strengthening in the grain and grain boundary.
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  • AlN Crystal Growth Using Interfacial Property between Molten Iron and Solid Alumina
    Hiroki Goto, Masanori Suzuki, Toshihiro Tanaka
    2015 Volume 79 Issue 7 Pages 356-361
    Published: 2015
    Released on J-STAGE: July 01, 2015
    DOIhttps://doi.org/10.2320/jinstmet.J2015003
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      Various methods of aluminum nitride (AlN) crystal growth have been attempted since AlN was first recognized as a ceramic material with remarkable properties, but no efficient method has yet been established. However, AlN is a well-known inclusion in the steelmaking process, and AlN crystal growth occurs in molten steel containing Al and N. This fact indicates that the crystal growth of AlN can easily occur in liquid iron alloy, but so far the role of the liquid iron has not been elucidated. In this work, the authors propose a new mechanism for AlN growth in molten iron, in which AlN crystals nucleate and grow at the interface between liquid iron and a solid Al2O3 substrate to decrease the large interfacial free energy between them. To investigate the interfacial chemistry between the liquid metal and solid oxide, we successfully produced needle-like, micro-size AlN crystals at the interface of molten iron and solid alumina by blowing N2 gas through a liquid iron alloy containing Al. We discuss the mechanism for the formation of various AlN crystal shapes at the interface between molten iron and solid alumina.
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  • Hydrogen Generation Monitoring and Mass Gain Analysis during the Steam Oxidation for Zircaloy Using Hydrogen and Oxygen Sensors
    Michihisa Fukumoto, Takuya Sakuraba, Motoi Hara, Hiroyuki Kaneko
    2015 Volume 79 Issue 7 Pages 362-371
    Published: 2015
    Released on J-STAGE: July 01, 2015
    DOIhttps://doi.org/10.2320/jinstmet.J2015002
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      The oxidation behavior of Zircaloy-4 at high temperatures in a flowing Ar-H2O (saturated at 323 K) mixed gas was investigated using hydrogen and oxygen sensors installed at a gas outlet, and the utility of the gas sensing methods by using both sensors was examined. The generated amount of hydrogen was determined from the hydrogen partial pressure continuously measured by the hydrogen sensor, and the resultant calculated oxygen amount that reacted with the specimen was in close agreement with the mass gain gravimetrically measured after the experiment. This result demonstrated that the hydrogen partial pressure measurement using a hydrogen sensor is an effective method for examining the steam oxidation of this metal as well as monitoring the hydrogen evolution. The advantage of this method is that the oxidation rate of the metal at any time as a differential quantity is able to be obtained, compared to the oxygen amount gravimetrically measured as an integral quantity. When the temperature was periodically changed in the range of 1173 K to 1523 K, highly accurate measurements could be carried out using this gas monitoring method, although reasonable measurements were not gravimetrically performed due to the fluctuating thermo-buoyancy during the experiment. A change of the oxidation rate was clearly detected at a monoclinic tetragonal transition temperature of ZrO2. From the calculation of the water vapor partial pressure during the thermal equilibrium condition using the hydrogen and oxygen partial pressures, it became clear that a thermal equilibrium state is maintained when the isothermal condition is maintained, but is not when the temperature increases or decreases with time.
       Based on these results, it was demonstrated that the gas monitoring system using hydrogen and oxygen sensors is very useful for investigating the oxidation process of the Zircaloy in steam.
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    Editor's pick

    Best Paper Award 2016

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  • Extrusion Sintering of Harmonic-Structured Composite with Ti-48 mol%Al Alloy and Pure Titanium by SPS Process
    Hiroshi Fujiwara, Reo Yoshida, Tatsuro Tsuda, Hiroyuki Miyamoto
    2015 Volume 79 Issue 7 Pages 372-375
    Published: 2015
    Released on J-STAGE: July 01, 2015
    DOIhttps://doi.org/10.2320/jinstmet.J2015020
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      A harmonic-structured composite with a fine grain Ti-48 mol%Al alloy network and dispersed coarse grain pure titanium is produced by extrusion sintering using the spark plasma sintering (SPS) process. The conditions of extrusion sintering by the SPS process are a sintering temperature of 1073 K, a holding time of 1.8 ks and an extrusion pressure of 100 MPa with a pressurization rate of approximately 0.1 MPa/s. The extrusion compact has a rod shape with φ5×48 mm. The extrusion compact is composed of an elongated harmonic structure with the Ti-48 mol%Al alloy network and the dispersed pure titanium. The Vickers hardness of the extrusion compact is about 220 Hv, which is almost the same as that of a conventional compact.
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  • Influence of Microelement Addition on the Pitting Corrosion Resistance of Nitrogen-Containing Stainless Steel
    Kazuma Miura, Narumi Hayashi, Masayuki Nakagawa, Hideki Okada, Kunio N ...
    2015 Volume 79 Issue 7 Pages 376-383
    Published: 2015
    Released on J-STAGE: July 01, 2015
    DOIhttps://doi.org/10.2320/jinstmet.J2015004
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      To improve the performance of stainless steel, we subjected solid-state steel to a nitrogen absorption treatment. In the fabrication process, a commercially available high-chromium ferritic stainless steel (Fe-22Cr-1Mo) was heat-treated at 1423 K in a nitrogen atmosphere. The heat-treatment transformed the ferric phase into the austenite phase. This process loaded over 1 mass% of nitrogen into the steel material. Most of the added nitrogen formed a solid solution in the matrix, but a minor portion formed nitrides with the very small quantities of elements such as titanium and aluminum that pre-existed in the steel. The nitrogen-containing steels were then analyzed by pitting potential measurements and ferric chloride corrosion examination. The pitting corrosion resistance of Fe-22Cr-1Mo-1N exceeded that of conventional materials such as Fe-18Cr-12Ni and Fe-22Cr-1Mo. However in the ferric chloride corrosion tests, pits developed in Fe-22Cr-1Mo-1N at temperatures above 323 K. These pits were possibly initiated at the sites of minute nitride resulting from the nitrogen absorption process.
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