Muraran Institute of Technology


Muraran Institute of Technology

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Komazak S.-I.,Kagoshima University | Konishi Y.,Muraran Institute of Technology | Kanaya A.,Kyushu Electric Power | Watanabe H.,Kyushu Electric Power | Kusumoto J.-I.,Kyushu Electric Power
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2011

Modification of small punch (SP) creep test was investigated to develop a new procedure for evaluating the creep property and damage of welded joint of high Cr ferritic steels by a miniaturized specimen. Disk and square-types specimens are usually clamped between the upper and lower dies in the isotropic manner in the conventional SP creep test, whereas the specimen used in this study was rectangular (10 × 6 × 0.50t mm) and was clamped at both ends of the specimen. This newly proposed SP creep test was applied to the welded joint of P122 steel pipe, which had been actually used in a fossil power plant for a long time. The specimens were removed from the mid section of the thickness of pipe so that the HAZ was located on the center of specimen perpendicular and parallel to the longitudinal direction of specimen respectively. In addition, the rectangular specimen consisting of only base metal and the conventional SP test specimen (10 × 10 × 0.50 t mm) with the HAZ were also subjected to the SP creep test for comparisons. Experimental results revealed that, by arranging the HAZ perpendicular to the longitudinal direction, the creep rupture strength decreased significantly reflecting the lower strength of the fine grain HAZ (FGHAZ). This decrease in creep strength was attributable to the acceleration of initiation and growth of cavity and/or microcrack at the FGHAZ. Consequently, it is indicated that the present modified SP creep testing technique has a high potential as a tool for evaluating the susceptibility to Type IV cracking and/or the creep damage of welded joints. © 2011 The Society of Materials Science, Japan.

Komazaki S.-I.,Muraran Institute of Technology | Honda T.,Muraran Institute of Technology | Sakamura T.,Muraran Institute of Technology | Sawada K.,Mitsubishi Group | And 2 more authors.
Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan | Year: 2010

Hydrogen is usually trapped by vacancy, dislocation, grain boundary, precipitate and void in steels and it is easily released from these trap sites by heating the steels. However, the desorption temperature ranges vary according to the kinds of trap sites and they can be separated in principle, because the binding energy between hydrogen and each trap site is different. It seems that this interesting nature of hydrogen is available for determining microstructural changes and defect formation processes during creep. In this study, the change in hydrogen desorption characteristic due to creep was investigated to discuss the applicability of this technique as a nondestructive procedure for evaluating creep damage accumulation of high Cr ferritic steels. The gauge and grip portions of creep ruptured specimens with different rupture times were charged with hydrogen by means of cathodic electrolysis. Subsequently, the thermal desorption spectroscopic (TDS) analysis was applied to those hydrogen-charged samples for measuring hydrogen desorption curve. Experimental results revealed that a clear peak appeared on the hydrogen desorption curve at around 65°C for the as-tempered. The peak temperature and the peak height of the gauge portion increased significantly resulting in the increase in amount of desorbed hydrogen as the creep rupture time increased, although those of the grip portion showed almost no difference. These changes in hydrogen desorption characteristic seemed to be attributable to the formation of geometric damages such as a creep cavity and microcrack rather than the microstructural changes, because the re-normalizing had almost no influence on the hydrogen desorption curve of the gauge portion.

Hayashi S.,Muraran Institute of Technology | Satoh K.,Muraran Institute of Technology | Satoh K.,Japan Institute for Environmental Sciences | Itoh H.,Muraran Institute of Technology
IEEJ Transactions on Fundamentals and Materials | Year: 2010

The variations in the partial pressures of gaseous molecules produced by the decomposition of C 6H 6 in a low pressure DC glow discharge in N 2/C 6H 6 and Ar/C 6H 6 mixtures are measured by the mass spectrometry. Also, rate equations for the partial pressure variations, which consider possible reaction among the gaseous molecules in the low pressure DC glow discharge, with the electrical energy-input, are proposed, and rate constants are determined by fitting the calculated partial pressure variations to the measured partial pressure variations. The rate constants deduced here indicate that C 6H 6 is mainly decomposed into an intermediate, which is regarded as a fragment of C 6H 6, the intermediate is decomposed into mainly C 2H 2, and then C 2H 2 is converted into H 2 and HCN (only in N 2/C 6H 6). © 2010 The Institute of Electrical Engineers of Japan.

Kudo Y.,Muraran Institute of Technology | Murai T.,Hokkaido University
2014 Joint 7th International Conference on Soft Computing and Intelligent Systems, SCIS 2014 and 15th International Symposium on Advanced Intelligent Systems, ISIS 2014 | Year: 2014

Interrelationship mining, proposed by the authors, enables us to extract characteristics based on comparison between values of different attributes. One of the main ideas of the interrelationship mining is to explicitly represent characteristics based on comparison between values of different attributes by new attributes called interrelated attributes. In this paper, we discuss properties of interrelated attributes that appear in relative reducts. © 2014 IEEE.

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