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보자력 측정에 의한 아공석강 및 공석강의 열처리에 따른 미세조직 평가
변재원,김정석,권숙인,Byeon Jai Won,Kim C. S.,Kwun S. I. 한국재료학회 2004 한국재료학회지 Vol.14 No.8
The microstructures of variously heat treated hypoeutectoid($0.45\%$ carbon) and eutectoid($0.85\%$ carbon) steel were characterized by magnetic coercivity measurement. The effect of spheroidization of cementites on the coercivity was investigated for $0.45\%$ carbon steel. In case of $0.85\%$ carbon steel, microstructural parameters such as prior austenite grain size, phase and pearlite interlamellar spacing were measured along with coercivity to investigate the relationships between them. Prior austenite grain size had little effect on the measured coercivity. Coercivity was observed to be high in order of martensite, pearlite and ferrite phases. The linear decrease of coercivity with increasing pearlite interlamellar spacing was found. The effect of each microstructural factor on the coercivity and the potential of coercivity as a nondestructive evaluation parameter for assessing microstructures of steel products are discussed.
자기적 방법에 의한 0.85% 탄소강의 열처리에 따른 미세조직 및 기계적 성질 평가
변재원,권숙인,Byeon, Jai-Won,Kwun, S.I. 한국재료학회 2003 한국재료학회지 Vol.13 No.2
Microstructures and mechanical properties of variously heat treated 0.85% carbon steel(eutectoid steel) were evaluated by magnetic property measurements. Microstructural analysis (pearlite interstellar spacing), measurement of mechanical properties(Rockwell hardness, yield stress, fracture stress) and magnetic properties(coercivity, remanence, hysteresis loss, saturation magnetization) were performed to clarify mutual relationships among these parameters. Water quenched specimens with martensite structure showed much higher coercivity and remanence than air cooled or furnace cooled specimens with pearlite structure. The linear dependence of coercivity and remanence on pearlite interlamellar spacing as well as on Rockwell hardness, yield stress and fracture stress was observed in the pearlitic steel. Hysteresis loss and saturation magnetization showed no distinct trend with pearlite interlamellar spacing.
인공 경년열화 열처리된 2.25CrMo 강에서의 고용원소 고갈 및 탄화물 변화
변재원(Jai Won Byeon),표승우(S. W. Pyo),권숙인(S. I. Kwun) 한국열처리공학회 2002 熱處理工學會誌 Vol.15 No.2
N/A The depletion of solid solution elements from matrix and the change of carbides during artificial aging of 2.25CrMo steel at 630℃ were investigated. The Mo and Cr elements were found to be depleted drastically in the early stage of aging. The change of carbides was confirmed by analyzing the XRD patterns of electrolytically extracted carbides. Four type of carbides, M_23C_6, M_3C, M_2C and M_6C, were found to exist in the specimen before aging. The amount of M_6C carbides increased with aging time, while that of M_3C carbides diminished after short aging time.
파괴적, 비파괴적 평가법을 이용한 터빈로터강의 열화도 평가
변재원(Jai Won Byeon),권숙인(S. I. Kwun),박은수(U. S. Park),박익근(I. K. Park) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
The ferritic 2.25CrMo steel has been used for high temperature structure applications such as turbine rotors, boilers and pressure vessels in fossil plant and petroleum chemical facilities. However, this steel is known to result in aging degradation due to temper embrittlement, carbide induced brittleness and softening of matrix after long time exposure to high temperature. This research investigated the microstructural and mechanical changes after artificial degradation treatment and evaluated the degree of degradation by several nondestructive methods. The increase of attenuation of ultrasonic wave and the decrease of magnetic coercivity with increasing aging time were observed. The change of magnetic coercivity showed a good correlation with the ductile-brittle transition temperature.
휴대전자기기용 저용량 리튬이온 배터리의 충방전 열화 기구 분석 및 모니터링
변재원(Byeon, Jai Won) 한국신뢰성학회 2013 신뢰성응용연구 Vol.13 No.2
As a fundamental experimental study for reliability improvement of lithium ion secondary battery, degradation mechanism was investigated by microscopic observation and acoustic emission monitoring. Microstructural observation of the decomposed battery after cycle test revealed mechanical and chemical damages such as interface delamination, microcrack of the electrodes, and solid electrolyte interphase (SEI). Acoustic emission (AE) signal was detected during charge and discharge of lithium ion battery to investigate relationships among cumulative count, discharge capacity, and microdamages. With increasing number of cycle, discharge capacity was decreased and AE cumulative count was observed to increase. Observed damages were attributed to sources of the detected AE signals.
인공 열화 열처리된 2.25CrMo 강의 미세조직 변화에 대한 초음파 비파괴평가
변재원(Jai Won Byeon),권숙인(S . I . Kwun),박은수(Un Su Park),박익근(Ik Keun Park) 한국열처리공학회 2001 熱處理工學會誌 Vol.14 No.2
N/A Artificial aging was performed to simulate the microstructural degradation in 2.25CrMo steel arising from long time exposure at 540℃. It was found that the carbides became coarser and spheroidized as aging time increased. An attempt was made to evaluate the microstructural degradation in artificially aging heat treated 2.25CrMo steel by the ultrasonic attenuation and velocity measurements. Ultrasonic velocity was found essentially insensitive to the microstructural changes resulting from aging heat treatment. However, the ultrasonic attenuation was observed to increase with increasing aging time. Also, it was noticed that the change of ultrasonic attenuation with aging time was more sensitive at high frequency regions.
경년열화 열처리된 2. 25CrMo 감에서의 탄화물 특성 및 자기적 성질의 변화
변재원(Jai Won Byeon),권숙인(S . I . Kwun) 한국열처리공학회 2001 熱處理工學會誌 Vol.14 No.6
N/A Artificial aging was performed to simulate the microstructural degradation in 2.25CrMo steel arising from long time exposure at 540℃. The carbide morphologies were classified as acicular, pipe and globular type, and the number of carbides per unit area was measured for each type of carbides. The fine acicular carbides were found to diminish drastically in the initial stage of aging. An attempt was made to evaluate the microstructural degradation in artificially aging heat treated 2.25CrMo steel by the magnetic property measurements such as saturation magnetization, coercivity and remanence. The saturation magnetization showed no distinct trend with aging time. However, the coercivity and remanence were observed to decrease rapidly in initial 920 hours of aging time and then decrease slowly afterwards.
플렉서블 CIGS 태양전지의 고온고습 환경 고장 기구 분석
김혁수(Hyeok-Soo Kim),변재원(Jai-Won Byeon) 한국신뢰성학회 2016 신뢰성응용연구 Vol.16 No.1
Purpose: The purpose of this study was to evaluate electrical and structural degradation of flexible CIGS sollar cell exposed to high temperature and humid atmosphere. Method: Accelerated degradation was performed for various time under 85℃/85%RH and then electrical and structural properties were analyzed by 4-point probe method, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Results: Sheet resistance of the top ITO layer increased with exposure time to the high temperature and humid atmosphere. Blunting of the protrusion morphology of ITO layer was observed for the degraded specimen, while no phase change was detected by XRD. Oxygen was detected at the edge area after 300 hours of exposure. Conclusion: Increase in electrical resistance of the degraded CIGS solar cell under high temperature and humid environment was attribute to the oxygen or water absorption.