熱起電力法を用いた鋳造2相ステンレス鋼の熱時効による材料劣化の非破壊評価 [in Japanese] Non-Destructive Evaluation of Thermal Aging of Cast Duplex Stainless Steel Using Thermoelectric Power Measurement [in Japanese]
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Cast duplex stainless steel is frequently used in main coolant pipes of PWR (Pressurized water reactor) type nuclear power plants because of its excellent material strength, toughness and superior corrosion resistance. However, it is known that material deterioration referred to as thermal aging occurs when this material is exposed to temperatures over 300°C. As a result, the material toughness decreases. Therefore, in managing the components made of cast duplex stainless steel, it is necessary to evaluate non-destructively such deterioration. In this study, measurement of thermoelectric power, which is sensitive to microstructural change in materials, was used for the evaluation of thermal aging. First, we investigated change in mechanical properties (hardness, tensile stress and notch toughness) due to thermal aging in cast duplex stainless steel. Secondly we measured thermoelectric power (TEP) and investigated change in TEP due to thermal aging and the effect of temperature of a specimen on TEP. Then the TEP was compared with the mechanical properties. As a result, TEP increases with aging time and the tendency becomes more remarkable as ferrite content increases. The increase in TEP of a specimen with 21.3% ferrite due to thermal aging (400°C-10000 h) is 0.61 μV/°C. The TEP slightly decreases with temperature of the specimen at a rate of about −0.009 μV/°C<SUP>2</SUP>. Finally we found good correlation between the TEP and ductile-brittle transition temperature, the TEP and notch toughness at 325°C. The correlation coefficients are respectively 0.886∼0.957 and −0.890∼−0.978. Therefore, by using TEP measurement, material deterioration of cast duplex stainless steel due to thermal aging can be evaluated.
- Journal of the Japan Institute of Metals and Materials
Journal of the Japan Institute of Metals and Materials 66(4), 377-383, 2002-04-20
The Japan Institute of Metals and Materials