스페이서 가터 스프링 코일 X-750 소재 정밀 조직 분석 방법

진형하,류이슬,이경근 한국압력기기공학회 2021 한국압력기기공학회 논문집 Vol.17 No.2

In the periodic surveillance material test for the spacer component of fuel channel assembly in CANDU, a microstructural characterization analysis is required in addition to the mechanical property evaluation test. In this study, detailed microstructure analysis and simple mechanical property evaluation of archive spacer parts were conducted to indirectly support the surveillance test and assist in the study of spacer material degradation. We investigated the microstructural characteristics of the spacer garter spring coil through comparative analysis with the plate material. The main microstructure characteristics of the garter spring coil X-750 are represented by the fine grain size distribution, the ordering phase distribution developed inside the matrix, the high dislocation density inside the grains, and the arrangement of coarse carbides. In addition, the yield strength of the garter spring coil X-750 was indirectly evaluated to be approximately 1 GPa. We also established an analytical method to elucidate the microstructural evolution of the radioactive spacer garter spring coil X-750 based on Canadian research experiences. Finally, we confirmed the measurement technique for helium bubble formation through TEM examination on the helium implanted X-750 material

집속이온빔 가공 처리된 오스테나이트 스테인리스강의 표면 손상층 제어 방법

진형하,류이슬 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.2

There is substantial concern about the phase change to artificial ferrite or martensite in commercialaustenitic stainless steels during intense focused-ion-beam milling. In this work, severe Ga ion milling toprepare microscale samples was found to produce thin transformed layers on the surface of austenitic stainlesssteel. The surface BCC phase transformation layer was clearly distinguished on the specimen processed withthe focused ion beam using cross-sectional analysis. It was determined that Ga ions had accumulated in thesurface BCC layer. However, it was also confirmed that the Ga ion accumulation was localized at the top ofthe surface. This is expected to be caused by the decrease in the formation energy of the body-centeredcrystalline phase, which may result from the considerable changes in chemical composition and stress stateby the accumulation of implanted Ga atoms. We propose an effective method to overcome the phase changeproblem caused by FIB, by using low-energy Ar ion milling. It was determined that low-energy FIB millingwas insufficient by itself to clear the phase transformation layer. High quality micro-scale experimentalsamples of austenitic stainless steels can be achieved by additional low-energy Ar ion milling at an energyof 1 keV or less after high-energy FIB milling.

Atom probe tomography analysis of nanostructure evolution in Ni-Cr-Mo low alloy steel under neutron irradiation

이경근,진형하,장근옥,임상엽,김민철,이봉상,권준현 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.8

Ni-Cr-Mo low alloy steels are being considered as alternative materials to replace the Mn-Mo-Ni low alloy steels used in reactor pressure vessels in nuclear power plants, because of their higher strength and toughness. However, the neutron irradiation occurring during reactor operation causes degradation of Ni-Cr-Mo low alloy steel. In this study, irradiation-induced clusters in a Ni-Cr-Mo model alloy irradiated in the High-flux advanced neutron application reactor (HANARO) research reactor were investigated via Atom probe tomography (APT). The irradiated specimens showed irradiation-induced hardening and embrittlement. The neutron irradiation caused Si clustering, and these spherical clusters were homogeneously distributed within the matrix. Ni was also clustered at the Si clusters. However, the other elements did not clearly exhibit clustering behavior. Si and Ni atoms were also located at the dislocations. To quantify the nano-sized clusters, a method based on the Density-based spatial clustering of applications with noise (DBSCAN) algorithm was implemented. The total number of clusters was calculated to be ~7 × 10 -4 n/nm 3 and the average cluster radius was less than 2 nm. The APT approach was demonstrated to be well suited for discovering the irradiation defect structures.

Radiation Damage to Ni-based Alloys in Wolsong CANDU Reactor Environments

권준현,진형하,이경근,박동환 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.3

Radiation damage due to neutrons has been calculated in Ni-based alloys in Wolsong CANDU reactorenvironments. Two damage parameters are considered: displacement damage, and transmutation gasproduction. We used the SPECTER and SRIM computer codes in quantifying radiation damage. In addition,damage caused by Ni two-step reactions was considered. Estimations were made for the annulusspacers in a CANDU reactor that are located axially along a fuel channel and made of Inconel X-750. Thecalculation results indicate that the transmutation gas production from the Ni two-step reactions ispredominant as the effective full power year increases. The displacement damage due to recoil atomsproduced from Ni two-step reactions accounts for over 30% out of the total displacement damage.

Selective Laser Melting 방식으로 적층제조된 Inconel 718 합금의 조사 경화 특성

서주원,임상엽,진형하,천영범,강석훈,한흥남 한국분말재료학회 2023 한국분말재료학회지 (KPMI) Vol.30 No.5

An irradiation hardening of Inconel 718 produced by selective laser melting (SLM) was studied based on the microstructural observation and mechanical behavior. Ion irradiation for emulating neutron irradiation has been proposed owing to advantages such as low radiation emission and short experimental periods. To prevent softening caused by the dissolution of ' and '' precipitates due to irradiation, only solution annealing (SA) was performed. SLM SA Inconel 718 specimen was ion irradiated to demonstrate the difference in microstructure and mechanical properties between the irradiated and non-irradiated specimens. After exposing specimens to Fe3+ ions irradiation up to 100 dpa (displacement per atom) at an ambient temperature, the hardness of irradiated specimens was measured by nanoindentation as a function of depth. The depth distribution profile of Fe3+ and dpa were calculated by the Monte Carlo SRIM (Stopping and Range of Ions in Matter)-2013 code under the assumption of the displacement threshold energy of 40 eV. A transmission electron microscope was utilized to observe the formation of irradiation defects such as dislocation loops. This study reveals that the Frank partial dislocation loops induce irradiation hardening of SLM SA Inconel 718 specimens.

改憲秘史

윤길중,조영규,진형하,김갑수,이석제,김문룡,김효전(편) 동아대학교 법학연구소 2016 東亞法學 Vol.- No.72

Multilevel modeling of diametral creep in pressure tubes of Korean CANDU units

이경근,안동현,진형하,송명호,정종엽 한국원자력학회 2021 Nuclear Engineering and Technology Vol.53 No.12

In this work, we applied a multilevel modeling technique to estimate the diametral creep in the pressuretubes of Korean Canada Deuterium Uranium (CANDU) units. Data accumulated from in-service inspections were used to develop the model. To confirm the strength of the multilevel models, a 2-levelmultilevel model considering the relationship between channels for a CANDU unit was comparedwith existing linear models. The multilevel model exhibited a very robust prediction accuracy comparedto the linear models with different data pooling methods. A 3-level multilevel model, which consideredindividual bundles, channels, and units, was also implemented. The influence of the channel installationdirection was incorporated into the three-stage multilevel model. For channels that were previouslymeasured, the developed 3-level multilevel model exhibited a very good predictive power, and theprediction interval was very narrow. However, for channels that had never been measured before, theprediction interval widened considerably. This model can be sufficiently improved by the accumulationof more data and can be applied to other CANDU units

H형강 플랜지 두께방향 위치별 나노인덴테이션 맵핑

김진혁,김상은,유경식,신찬선,진형하,문준오,이창훈 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11

내진 특성 (낮은 항복비)과 내화 특성 (높은 고온강도)을 동시에 확보하기 위한 합금 설계와 H형강 제조를 위한 QST (Quenching and self-Tempering) 제조공정의 최적화 연구가 진행중이다. QST 공정에 의한 열간 압연 및 냉각 시 소재에는 위치 별 냉각 속도의 차이가 발생하며 이는 잔류 응력과 미세조직의 차이를 유발할 수 있다. 이 연구에서는 QST 공정으로 제작된 420MPa급 건축용 내화/내진 H형강의 고온 노출 전/후의 플랜지 두께 방향 위치 별 물성과 미세조직 차이와 변화를 평가하고자 한다. 현대제철 QST 설비를 통해 제조한 폭 700mm, 높이 300mm, 플랜지 두께 24mm인 H형강에서 플랜지 두께 방향 위치별로 10×10×2 mm 시편을 채취하였다. 화재 상황을 모사하기 위해 600℃ 온도에서 2시간 노출한 시편을 제작하였다. 이렇게 제작된 고온 노출 전/후의 시편 표면을 전해 연마하고 EBSD (Electron Backscatter Diffraction)를 통한 미세조직 분석과 나노인덴테이션 맵핑을 통한 나노경도 및 탄성계수의 공간적 분포를 평가하였다. 나노인덴테이션 맵핑 시 공간 분해능을 높이고 표면의 영향을 배제하기 위해 압입 간격과 압입 깊이를 조절하였다. 실험결과 플랜지 표면에서 깊이 400 μm까지는 페라이트와 펄라이트 조직이 형성되었으며 그 내부에는 베이나이트가 우세한 조직이 형성되었다. 100×100 μm 영역에서 75×75개 나노압입을 통한 나노경도 및 탄성계수 맵핑을 성공적으로 수행하였으며 이를 통해 페라이트와 펄라이트, 그리고 베이나이트의 상을 구분할 수 있었다. 고온 노출 전/후의 나노경도 분포의 변화를 분석한 결과 고온 노출에 의해 6GPa 이상의 상이 대부분 사라졌으나 평균 나노경도 값은 고온 노출 전과 큰 차이가 없었다. 이는 개발 강재가 600℃ 2시간 고온 노출 후에도 미세조직과 강도를 잘 유지함을 나타낸다.

420MPa급 H형강 플랜지 두께방향 위치별 미세조직과 나노경도분포 차이 분석

신찬선,김진혁,김상은,유경식,진형하,문준오,이창훈 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5

복잡한 형강 제조기술인 QST (Quenching & Self tempering) 공정 특성 상 소재 위치 별 온도 이력이 상이하고 그 결과 미세조직과 기계적 물성에 차이가 발생할 수 있다. 이 연구에서는 항복강도 420MPa급 건축용 H형강의 플랜지 두께방향 위치에 따른 미세구조와 나노경도 분포를 실험적으로 분석하여 비교하였다. DS (Driving side) 플랜지의 상부와 하부의 가운데 부분에서 바깥쪽에서 웹 방향 두께별로 각각 세 개의 시편 (외곽 표면부분, 가운데 부분, 웹방향 표면부분)을 채취하였다. 미세조직 분석결과 플랜지 외곽 표면부분과 가운데 부분의 경우 마르텐사이트와 베이나이트 미세조직을 보인 반면 웹방향 표면부분은 페라이트와 펄라이트 미세구조가 관찰되었다. 비커스 경도 측정 결과 상부 플랜지 외곽과 가운데 부분 및 하부 플랜지 가운데 부분의 값은 204~216HV이나 상부 플랜지 웹방향 표면부분 및 하부 플랜지 외곽 및 웹방향 표면부분은 156~168HV로 측정되었다. 나노압입 시험 결과 미세조직에 따라 2.7~6.3 GPa까지 나노경도가 분포하였으며 이는 각각 페라이트, 베이나이트 그리고 마르텐사이트의 나노경도값에 해당한다. 고속 나노압입시험을 통해 플랜지 각 위치별 나노경도 분포를 측정하고 이를 EBSD를 통해 분석한 미세조직과 비교하였다. 이를 통해 나노압입 매핑을 통한 상의 분리 및 분포 측정 결과를 교차 검증하였다. QST 공정의 온도 이력 차이에 의해 발생한 H형강 플랜지 두께방향 위치 별 상이한 미세조직 및 나노경도 분포를 정량화 하였다.