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2.25Cr강 보일러 튜브재료의 고온입계균열 발생 거동
유근봉(Keun Bong Yoo),허남회(Nam Hoe Heo),장중철(Jung Chel Jang),김재훈(Jae Hoon Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Recently, a premature failure of boiler tubes or pipes has frequently occurred at several domestic power plants and most of the fracture type was intergranular. It has been well known that the elevated temperature intergranular cracking in heat-resistant steels occurs through the combination of closely spaced voids at the grain boundaries oriented normal to the tensile stress. However, what the mechanism of low ductility intergranular fracture induced by the tensile stress is are still obscure. In this study, we analyzed the behavior of the elevated temperature intergranular cracking in 2.25Cr-1.5W heat-resistant steels through stress-rupture test. We used the SEM(Scanning Electron Microscope) and AES(Auger Electron Spectroscopy) to investigate the fracture surface and segregation behavior.
유근봉(Keun Bong Yoo),이한상(Han Sang Lee),송규소(Gyu So Song),이규호(Kyu Ho Lee) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.12
고온의 연소가스에서 운전되는 국내 가스터빈 부품들은 매일 기동정지를 반복함으로써 열사이클에 의해 재료특성에 변화가 발생한다. 최근 많은 가스터빈 고온부품들이 단결정 초내열 합금으로 제작되어 지지만 재료열화 예측을 통한 부품 교체와 정비에 대한 기준이 없어서 대부분 제작사에 의존하고 있는 실정이다. 본 연구에서는 향후 수명평가와 손상분석의 기초자료로 활용하기 위해 실제 운전된 가스터빈 1 단 블레이드의 열화상태를 조사하였다. 사용한 블레이드는 25,000 및 52,000 의 등가운전시간(EOH : Equivalent Operating Hour)을 가졌으며, 재질은 단결정 초내열합금인 CMSX-4 이다. 사용된 블레이드에서 직접 시험편을 채취하여 기계적특성 시험 및 미세조직을 관찰하였다. The material properties of gas turbine components change during the daily start/stop thermal cycle because of exposure to the hot combustion gas. Recently, single-crystal Ni-based superalloys have been used to manufacture many hot-gas components for gas turbines. However, the user needs to depend on the manufacturer for maintenance issues because of the lack of data required for predicting blade life and material degradation. In this study, we investigate the time-dependent degradation of first-stage blades at various operating facilities to collect the basic data for life assessment and damage analysis. The blade material is a single-crystal Ni-based superalloy, CMSX-4, and the EOH (equivalent operating hours) are 25,000 and 52,000, respectively. We prepared the test specimen directly from used blades and carried out mechanical tests and microstructural observations.
X선 회절을 이용한 용접부의 잔류응력 평가 및 피로수명 예측
유근봉(Keun Bong Yoo),김재훈(Jae Hoon Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
In the fossil power plant, the reliability of the components which consist of the many welded parts depends on the quality of welding. The residual stress is occurred by the heat flux of high temperature during weld process. This decreases the mechanical properties as the strength of fatigue and fracture or occurs the stress corrosion cracking and fatigue fracture. The residual stress of the welded part in the recently constructed power plants has been the cause of a variety of accidents. The objective of this study is measurement of the residual stress by X-ray diffraction method and to estimate the feasibility of this application for fatigue life assessment of the high-temperature pipeline. The materials used for the study is P92 steel for the use of high temperature pipe on super critical condition. The test results were analyzed by the distributed characteristics of residual stresses and the full width at half maximum intensity (FWHM) in x-ray diffraction intensity curve. Also, X-ray diffraction tests using specimens simulated low cycle fatigue damage were performed in order to analyze fatigue properties when fatigue damage conditions become various stages. As a result of X-ray diffraction tests for specimens simulated fatigue damages, we conformed that the ratio of the FWHM due to fatigue damage has linear relationship with fatigue life ratio algebraically. From this relationships, it was suggested that direct expectation of the life consumption rate was feasible.
유근봉(Keun Bong Yoo),이한상(Han Sang Lee),김두수(Doo Soo Kim),양호영(Ho Young Yang) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
The rotating components in the hot sections of land-based gas turbine are exposed to severe environment during several ten hours at above 1100℃ operating temperature. The failure mechanism of the hot gas components would be accompanied by material degradation in the properties of high temperature strength and creep rupture strength. Many hot gas components in gas turbine are made of Ni-based superalloy because of their high temperature performance. In this work, we survey the time and temperature dependent degradation of Ni-based superalloy. We prepared the specimen from IN738LC that are exposed at 871~982 ℃ in 1,000 ~ 10,000 hours. We carried out the mechanical test and microstructural observation.
유근봉(Keun-Bong Yoo),정남근(Nam-geun Jeong),이성호(Sung-Ho Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
The gas turbine components operating by hot combustion gas undergo damage by thermal fatigue or thermal stress due to the daily operation. A HGC acting as a chamber and inducting hot combustion gas to gas turbine from combustion liner is damaged after the operation of 4000hour. The HGC is somewhat large component. The crack developed to 90cm happened from thin, and stress-concentrated area. In this work, we survey HGC at the site with naked eye. After that, we observe not only the operational background, and characteristic of facilities but damaged component using optical microscope and scanning electron microscope to set up the counterplan by analyzing the reason of damage. Finally, we carry out the mechanical test, thickness measurement, and stress analysis at weakness area in order to avoid similar accident and make up the facilities.