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오스테나이트계 Fe-18Cr-10Mn-N-C 합금의 연성-취성 천이 거동에 미치는 결정립 크기의 영향
이상인,이승용,남승훈,황병철,Lee, Sang-In,Lee, Seung-Yong,Nam, Seung Hoon,Hwang, Byoungchul 한국재료학회 2015 한국재료학회지 Vol.25 No.10
The ductile-brittle transition behavior of two austenitic Fe-18Cr-10Mn-N-C alloys with different grain sizes was investigated in this study. The alloys exhibited a ductile-brittle transition behavior because of an unusual brittle fracture at low temperatures unlike conventional austenitic alloys. The alloy specimens with a smaller grain size had a higher yield and tensile strengths than those with a larger grain size due to grain refinement strengthening. However, a decrease in the grain size deteriorated the low-temperature toughness by increasing the ductile-brittle transition temperature because nitrogen or carbon could enhance the effectiveness of the grain boundaries to overcome the thermal energy. It could be explained by the temperature dependence of the yield stress based on low-temperature tensile tests. In order to improve both the strength and toughness of austenitic Fe-Cr-Mn-N-C alloys with different chemical compositions and grain sizes, more systematic studies are required to understand the effect of the grain size on the mechanical properties in relation to the temperature sensitivity of yield and fracture stresses.
스테인리스강 316L 수소가압-인장시험의 수소취성균열과 상변태
백운봉 ( Un Bong Baek ),최병학 ( Byung Hak Choe ),심종헌 ( Jong Hun Shim ),김영욱 ( Young Uk Kim ),김영석 ( Young Suk Kim ),김성수 ( Sung Soo Kim ),남승훈 ( Sung Hoon Nam ),홍기용 ( Key Yong Hong ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.2
The aim of this investigation is to prove the mechanism of hydrogen induced crack (HIC) of 316L stainless steels in hydrogen pressured tensile test. Microstructures like twin, planar slip, and abnormal phase transformation around the HIC were analyzed by transmission electron microscopy. Deformation twin accompanied by planar slip could be related to the main cause of HIC in the hydrogen pressured tensile condition, because intragranular HICs were mainly observed along the boundaries of twins and planar slip lines. An abnormal forbidden diffraction was also accompanied by HIC in the hydrogen attacked area. Examination of the HIC mechanism in austenitic stainless steel can be applied to the fitness of use for alloys with the possibility of various susceptible cracks in a hydrogen and stress atmosphere.
스테인리스강 316L 배관의 End Grain Attack과 피트부식 손상진단
백운봉 ( Un Bong Baek ),최병학 ( Byung Hak Choe ),이진희 ( Jin Hee Lee ),심종헌 ( Jong Hun Shim ),김의수 ( Eui Soo Kim ),남승훈 ( Sung Hoon Nam ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.1
The aim of this paper was to analyze the cause of surface cracks and pit corrosion on 316L pipe. An End Grain Attack (EGA) as a kind of pit mechanism was conducted on the pipe surface. The early stage of the EGA may come from under-deposit of caustic-water formation compositions like Na+, K+, Ca+, and Mg+ etc. The under-deposit corrosion is caused by the corrosion layer on the pipe surface followed by crevice corrosion due to accumulation of Cl-or S-composition between the corrosion layer and the pipe surface. In the early stage, the EGA occurred in all grain boundaries beneath the under-deposit corrosion. In the later stage of EGA, almost all the early attacked grain boundaries stopped at a limited depth of about 10 μm. Meanwhile, only the smallest number of the attacked boundaries progressed into the pipe as pit corrosion and resulted in leak failure. (Received February 24, 2014)