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소형시험편의 Master Curve 방법을 이용한 원자로 압력용기강의 파괴인성 천이특성평가
양원존,허무영,김주학,이봉상,홍준화,Yang, Won-Jon,Heo, Mu-Yeong,Kim, Ju-Hak,Lee, Bong-Sang,Hong, Jun-Hwa 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.2
Fracture toughness of five different reactor pressure vessel steels was characterized in the transition temperature region by the ASTM E1921-97 standard method using Charpy-sized small specimens. T he predominant fracture mode of the tested steels was transgranular cleavage in the test conditions. A statistical analysis based on the Weibull distribution was applied to the interpretation of the scattered fracture toughness data. The size-dependence of the measured fracture toughness values was also well predicted by means of the Weibull probabilistic analysis. The measured fracture toughness transition curves followed the temperature-dependence of the ASTM master curve within the expected scatter bands. Therefore, the fracture toughness characteristics in the transition region could be described by a single parameter, so-called the reference temperature (T。), for a given steel. The determined reference temperatures of the tested materials could not be correlated with the conventional index temperatures from Charpy impact tests.
베이나이트계 저합금강의 천이온도영역에서 취성파괴에 미치는 결정립 크기의 영향 고찰
양원존,이봉상,김민철,홍준화,허무영 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.12
The effects of the prior austenite grain size on the cleavage fracture toughness were investigated in the transition region of bainitic low alloy steels. Cleavage fracture toughness was evaluated by the ASTM standard E 1921. Yield strengths satisfied the Hall-Petch relationship, but fracture toughness in the transition region did not show significant dependence on the austenite grain size. Fracture surfaces showed that the facet size was related to the austenite grain size, but cleavage initiation distance(CID) from the original crack tip showed no direct relationship to the grain and facet sizes. Therefore, the austenite grain size may have little effects on the fracture toughness of bainitic low alloy steels in the transition region. In the viewpoint of the weakest link theory, particle distribution in front of the crack tip is probably more important than the grain size in the transition temperature range where fracture was controlled by cleavage crack initiation. The experimental results in this study supported the weakest-link-theory.