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고온전기분해시스템의 열교환기 후보재료에 대한 고온증기 환경에서의 부식평가 현황
김민우,김동훈,장창희,윤덕주,Kim, Minu,Kim, Dong Hoon,Jang, Changheui,Yoon, Duk-Joo 한국압력기기공학회 2009 한국압력기기공학회 논문집 Vol.5 No.1
본 논문에서는 국제적으로 개발 중인 초고온가스로와 연계하여 대량의 수소를 생산하기 위한 방안의 일환으로 국내에서 개발 중인 고온증기전기분해 시스템에 사용될 열교환기 재료의 고온증기 부식실험에 대해 소개하였다. 이를 위해 관련된 국내외 연구현황을 조사분석한 결과를 요약하여 소개하였으며 마지막으로 현재 수행중인 고온증기부식 연구의 실험조건 및 계획을 제시하였다. 실험 및 연구결과는 초고온가스로와 연계된 고온전기분해를 이용한 수소생산시스템의 개발에 활용될 예정이다. Nuclear hydrogen production using high temperature heat of a very high temperature reactor(VHTR) is one of the most attractive ways of mass hydrogen production without greenhouse gas emission. In many countries, sulfur-iodine(S-I) thermochemical process and high temperature steam electrolysis(HTSE) process are being investigated. In such processes, corrosion behavior of Intermediate heat exchanger materials are the most critical issues. Especially in a HTSE system, several heat exchangers will be facing hot steam conditions. In this paper, the status of high temperature corrosion researches in hot steam and supercritical water conditions are reviewed in view of the implication to HTSE conditions. Based on the review, test condition and plan of the hot steam corrosion of the candidate materials are formulated and described in some details along with the schematics of the test set-up. The test results and subsequent evaluation will be used in development of a interface system between the HTSE hydrogen production system and the VHTR.
가속 열시효에 따른 308 및 316L 스테인리스강 용접부의 기계적 물성 및 미세구조 평가
공병서,홍성훈,장창희,김만원,Kong, Byeong Seo,Hong, Sunghoon,Jang, Changheui,Kim, Maan-Won 한국압력기기공학회 2017 한국압력기기공학회 논문집 Vol.13 No.1
Due to the presence of ferrite phase in the finished welds, austenitic stainless steel welds (ASSWs) are considered susceptible to the thermal aging embrittlement during long-term service in light water reactor environment. In this study, the thermal aging embrittlement of typical ASSWs, E308 and ER316L welds, were evaluated after the long-term exposure up to 20,000 h at $400^{\circ}C$, which is considered as an accelerated thermal aging condition. After thermal aging, the decrease of tensile ductility and fracture toughness was observed. The microstructure observation with high resolution transmission electron microscopy revealed that spinodal decomposition in ferrite phase of both E308 and ER316L welds would be the main cause of the degradation of mechanical properties. Also, it was shown that the difference of thermal ageing embrittlement between ER316L and E308 welds was significant, such that the reduction of fracture resistance for ER316L weld was much larger than that of E308 weld.
산소가 제거된 310 ℃ 순수환경에서 CF8M 주조 스테인리스강의 환경 피로거동ㆍ수소 및 미세구조의 영향
장훈(Hun Jang),조평연(Pyungyeon Cho),장창희(Changheui Jang),김태순(Tae Soon Kim) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.1
CF8M (11% ferrite) 주조 스테인리스강의 310 ℃ 순수환경에서의 저주기피로 수명에 미치는 수소 및 미세구조의 영향을 분석하였다. CF8M 의 경우, 공기환경 대비 310 ℃ 순수환경에서의 피로수명의 감소는 단조재인 316LN 에 비해 다소 작았다. 미세구조 및 파면 분석을 통해, CF8M 의 저주기피로 수명의 감소는 316LN 의 경우와 마찬가지로 수소유기균열에 의한 것으로 판단되었다. 그러나, CF8M 의 경우, 페라이트상 경계에 수소유기균열에 의한 2 차 균열이 빈번히 발생함에 따라 균열 선단에서의 응력집중이 저하되는 효과가 있었다. 이러한 응력집중의 완화로 인해 수소유기균열에 의한 피로균열진전이 둔화 되어 결과적으로 저주기피로 수명의 저하가 완화되는 것으로 판단되었다. The effects of environment and microstructure on low cycle fatigue (LCF) behaviors of CF8M stainless steels containing 11% of ferrites were investigated in a 310 ℃ deoxygenated water environment. The reduction of LCF life of CF8M in a 310 ℃ deoxygenated water was smaller than 316LN stainless steels. Based on the microstructure and fatigue surface analyses, it was confirmed that the hydrogen induced cracking contributed to the reduction in LCF life for CF8M as well as for 316LN. However, many secondary cracks were found on the boundaries of ferrite phases in CF8M, which effectively reduced the stress concentration at the crack tip. Because of the reduced stress concentration, the accelerated fatigue crack growth by hydrogen induced cracking was less significant, which resulted in the smaller environmental effects for CF8M than 316LN in a 310 ℃ deoxygenated water.
산소 농도에 따른 Alloy 617의 고온헬륨환경에서의 크립 및 산화거동
구자현,김대종,장창희,Koo, Jahyun,Kim, Daejong,Jang, Changheui 한국압력기기공학회 2011 한국압력기기공학회 논문집 Vol.7 No.2
Wrought nickel-base superalloys are being considered as the structural materials in very-high temperature gas-cooled reactors. To understand the effects of impurities, especially oxygen, in helium coolant on the mechanical properties of Alloy 617, creep tests were performed in high temperature flowing He environments with varying $O_2$ contents at 800, 900, and $1000^{\circ}C$. Also, creep life in static He was measured to simulate the pseudo-inert environment. Creep life was the longest in static He, while the shortest in flowing helium. In static He, impurities like $O_2$ and moisture were quickly consumed by oxidation in the early stage of creep test, which prevented further oxidation during creep test. Without oxidation, microstructural change detrimental to creep such as decarburization and internal oxidation were prevented, which resulted in longer creep life. On the other hand, in flowing He environment, surface oxides were not stable enough to act as diffusion barriers for oxidation. Therefore, extensive decarburization and internal oxidation under tensile load contributed to premature failure resulting in short creep life. Limited test in flowing He+200ppm $O_2$ resulted in even shorter creep life. The oxidation samples showed extensive spallation which resulted in severe decarburization and internal oxidation in those environments. Further test and analysis are underway to clarify the relationship between oxidation and creep resistance.
확산접합된 페라이트/마르텐사이트강의 미세조직 및 기계적 특성에 미치는 열처리 효과
사인진,김성환,홍성훈,장창희,Sah, Injin,Kim, Sunghwan,Hong, Sunghoon,Jang, Changheui 한국압력기기공학회 2015 한국압력기기공학회 논문집 Vol.11 No.1
As a measure of improving the mechanical properties of a diffusion bonded joint of a ferritic/martensitic steel (FMS), the post-bonding heat treatment (PBHT) is applied. In the temperature range of normalizing condition ($950-1,050^{\circ}C$), diffusion bonding is employed with compressive stress (6 MPa). Due to the martensite structure distributed in the matrix, Vicker's hardness values of the as-bonded are much higher than those of the as-received. Through the PBHT for 1 h at $720^{\circ}C$, hardness values are recovered to as low as those of the as-received condition. Also, tensile properties of PBHT are similar to those of the as-received at up to the test temperature of $550^{\circ}C$, when the diffusion bonding is carried out over $1,000^{\circ}C$. Based on the creep-rupture testing performed at $650^{\circ}C$ in air environment, the joint efficiency of the PBHTed specimens is about 80% in, which is higher than that of the as-bonded specimens.