Papers by Author: Takayuki Sugimoto

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Authors: Jae Il Jang, Sang Hoon Shim, Shinichi Komazaki, Takayuki Sugimoto
Abstract: As advanced ferritic/martensitic heat-resistant steels generally have a complex structure consisting of several microstructural units (lath, block, packet, and prior austenite grain), it is very hard to separate the contribution of each microstructural unit (or its each boundary) to the strengthening mechanism in such steels. Here we explore the role of each microstructural unit in strengthening of advanced high Cr steel through nanoindentation experiments performed at different load levels. Nanoindentation results are analyzed by comparing with microstructural observations and discussed in terms of prevailing descriptions of strengthening mechanism.
Authors: Shinichi Komazaki, T. Nakata, Takayuki Sugimoto, Yutaka Kohno
Abstract: The recently developed small punch (SP) creep test was applied to four different heatresistant ferritic steels, namely, two kinds of conventional ferritic steels which had been actually used in the high-temperature components for long periods and two advanced high chromium ferritic steels for fusion reactor materials to investigate the applicability of the SP creep test. The ratio of the load of SP creep test to the stress of standard uniaxial creep test was calculated so that both the creep rupture curves (load/stress versus Larson-Miller parameter curves) were overlapped to convert the results of SP creep test into those of standard test. As a result, the ratio was determined to be 2.4, irrespective of the kind of ferritic steel. This result indicates that the creep rupture strength of heat-resistance ferritic steels can be estimated using a miniaturized plate-type specimen and this conversion coefficient 2.4 independent of the kind of ferritic steel.
Authors: Takayuki Sugimoto, Shinichi Komazaki, Toshihei Misawa
Abstract: Both the change in DBTT and the degradation of creep properties of the aged CrMoV cast steel which had been actually used as a main steam valve were evaluated from the conventional SP test and the SP creep (SP-C) test using by SP test specimens. The CVN DBTTs of the virgin and aged steels were estimated to be 280 and 369 K by the conventional SP test, respectively. This increase in DBTT after the long-term service exposure was considered to be caused by carbide-induced embrittlement due to coarse carbides. The SP-C test results revealed that the creep rupture strength of the aged steel was inferior to that of the virgin steel. The ratio, F / s , between the load of the SP-C test (F) and the stress of the uniaxial test ( s) was determined to be 2.4 for the same value of the Larson-Miller parameter in the creep rupture data. This linear relationship enables us to convert the results of the SP-C test into those corresponding to a conventional uniaxial creep test. Consequently, the SP testing method is expected to be appropriate tool for the determination of material deterioration and, in turn, the assessment of remaining-life of high-temperature components.
Authors: T. Honda, Shinichi Komazaki, Takayuki Sugimoto, Yutaka Kohno
Abstract: The thermally aged 10Cr-1Mo-1W-VNbN steels were charged with hydrogen by cathodic electrolysis and then were subjected to the thermal desorption spectroscopic analyses to examine an applicability of hydrogen as a tracer for evaluating the microstructure. The variation in hydrogen desorption characteristics with aging was discussed from the view points of microstructural changes. Experimental results revealed that the amount of hydrogen desorbed, CH, decreased monotonously as the aging proceeded and there was a relatively good correlation between the CH and Vickers hardness. The CH was expected to be a useful indicator for the material degradation. Additionally, the decomposition of the profile was attempted to understand the metallurgical meaning of hydrogen profile and apply the present method to the microstructural evaluation. As the result, it was suggested that the changes in two decomposed profiles with aging might reflect the variation of dislocation density and the precipitation process of M23C6 carbide and/or Laves phase, respectively.
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