Correlation of metallurgical analysis and higher harmonic ultrasound response for long term isothermally aged crept FM steels = 장기열화 및 크리프 손상된 FM강의 금속조직과 고조파 초음파 응답과의 연관성

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Higher harmonic ultrasound response of modified 9-12Cr Ferritic-Martensitic (FM) steel, long term isothermally aged and crept up to 25,000 hours near the operating temperature of Ultra-Super Critical (USC) Thermal Power Plants (TPP), was studied. Metallurgical analysis, including quantitative measurements of dislocation density and second phase distribution, revealed that the lath conversion to subgrain, Laves phase development and coarsening of pre-existing second phase MX and $M_{23}C_{6}$, and increased ultrasound attenuation are dominant effects on $beta$ parameter evolution with thermal aging. The possibility of a higher harmonic ultrasound technique to monitor the creep damage is quite obvious, since a substantial increase of roughly 2~300% was observed of the $beta$ parameter measurement results on long term crept material in this study. The major features of $beta$ parameter variation observed of crept material was (1) roughly linear correlation with Larson Miller Parameter (LMP), (2) large offset at low LMP and (3) gradual approach of two measurement group, material degradated with and without creep stress, at high LMP. Theoretical approximation for the contribution to $beta$ parameter and measurement results of ultrasound attenuation successfully verified that the increased ultrasound attenuation is one of the major contributors to $beta$ parameter variation of the material in question, in addition to the previously well studied dislocation density and second phase distribution.
Advisors
Jang, Chang-Heuiresearcher장창희
Description
한국과학기술원 : 원자력및양자공학과,
Publisher
한국과학기술원
Issue Date
2012
Identifier
511869/325007  / 020075282
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 원자력및양자공학과, 2012.8, [ x, 122 p. ]

Keywords

Harmonic distortion; Ultrasound; Ferritic-Martensitic; Creep; 고조파 왜곡; 초음파; 내열강; 크리프; 열손상; Thermal aging

URI
http://hdl.handle.net/10203/182215
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=511869&flag=dissertation
Appears in Collection
NE-Theses_Ph.D.(박사논문)
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