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논문 : 기계적 성질 ; Ll2 (Al, Cr)3 Ti기 2상 금속간화합물의 소성거동에 미치는 V 및 Zr 첨가의 효과
박정용 ( Jeong Yong Park ),오명훈 ( Myung Hoon Oh ),위당문 ( Dang Moon Wee ) 대한금속재료학회 ( 구 대한금속학회 ) 1998 대한금속·재료학회지 Vol.36 No.7
Effects of V and Zr additions on the microstructures and the mechanical properties of two-phase intermetallic compounds consisting of LI2 matrix and 20vol.% Cr2Al were investigated. Among the V-added two-phase intermetallic compounds, Al-2lTi-20Cr-3V showed the best ductility as well as relatively high yield strength. V was found to substitute for Cr and improve the ductility of Cr2Al phase, In the case of Zr-added two-phase alloys, the particle size of Cr2Al was refined, and Zr was found to be soluble only in Li matrix As Zr content increased in the Zr-added two-phase alloys, the yield strength increased, but the ductility decreased. It was found in Zr-added two-phase alloys that the loss of ductility in Li matrix due to Zr additions was more significant than the ductilizing effect due to second phase refinement. Zr-added two-phase alloys, however, shoed higher yield strength than V-added two-phase alloys over the entire temperature range tested. Based on the results obtained, plastic deformation behavior of two-phase intermetallic compounds alloyed with V and Zr were examined. Al-19Ti-21Cr-2V-2Zr showed the best mechanical properties among the alloys tested, which is suggested to be the alloy composition to optimize the effects of V and Zr additions simultaneously.
압력용기용 Ni-Mo-Cr계 고강도 저합금강의 P, Mn 함량에 따른 템퍼 취화거동 및 입계편석거동 평가
박상규 ( Sang Gyu Park ),김민철 ( Min Chul Kim ),이봉상 ( Bong Sang Lee ),위당문 ( Dang Moon Wee ) 대한금속·재료학회 2010 대한금속·재료학회지 Vol.48 No.2
Higher strength and fracture toughness of reactor pressure vessel steels can be obtained by changing the material specification from that of Mn-Mo-Ni low alloy steel (SA508 Gr.3) to Ni-Mo-Cr low alloy steel (SA508 Gr.4N). However, the operation temperature of the reactor pressure vessel is more than 300℃ and the reactor operates for over 40 years. Therefore, we need to have phase stability in the high temperature range in order to apply the SA508 Gr.4N low alloy steel for a reactor pressure vessel. It is very important to evaluate the temper embrittlement phenomena of SA508 Gr.4N for an RPV application. In this study, we have performed a Charpy impact test and tensile test of SA508 Gr.4N low alloy steel with changing impurity element contents such as Mn and P. And also, the mechanical properties of these low alloy steels after longterm heat treatment (450℃, 2000hr) are evaluated. Further, evaluation of the temper embrittlement by fracture analysis was carried out. Temper embrittlement occurs in KL4-Ref and KL4-P, which show a decrease of the elongation and a shifting of the transition curve toward high temperature. The reason for the temper embrittlement is the grain boundary segregation of the impurity element P and the alloying element Ni. However, KL4-Ref shows temper embrittlement phenomena despite the same contents of P and Ni compared with SC-KL4. This result may be caused by the Mn contents. In addition, the behavior of embrittlement is not largely affected by the formation of M3P phosphide or the coarsening of Cr carbides.
Si의 조성변화가 Al이 첨가된 ReSi(1.75) 단결정의 열전특성에 미치는 효과
오민욱 ( Min Wook Oh ),김민철 ( Min Chul Kim ),오명훈 ( Myung Hoon Oh ),위당문 ( Dang Moon Wee ),( Haruyuki Inui ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 대한금속·재료학회지 Vol.44 No.6
The thermoelectric properties of ReSi(1.73+x)Al(0.02) (-0.02 < × < 0.04) have been investigated in the temperature range between 323 and 1073 K. As a result of Al-addition, the electrical properties of the ternary at low temperatures are changed from the character of nondegenerate semiconductors, which is of binary ReSi(1.75), to that of degenerate semiconductors, and the band-gap along [001] becomes wider than that of the binary. The variation of Si composition affects the electrical properties along [100], but those along [001] are conserved. The change of the band structure due to the variation of Si composition is estimated with the result of the Seebeck coefficient at low and high temperatures. The maximum dimensionless figure of merit (ZT) along [100] is about 0.7 in the temperature between 473 and 773 K and along [001] is 0.67 at 1073 K.
논문 : 압력용기용 Ni-Mo-Cr계 고강도 저합금강의 합금원소 함량 변화에 따른 미세조직학적 특성변화의 열역학 계산 및 평가
박상규 ( Sang Gyu Park ),김민철 ( Min Chul Kim ),이봉상 ( Bong Sang Lee ),위당문 ( Dang Moon Wee ) 대한금속재료학회 ( 구 대한금속학회 ) 2008 대한금속·재료학회지 Vol.46 No.12
An effective way of increasing the strength and fracture toughness of reactor pressure vessel steels is to change the material specification from that of Mn-Mo-Ni low alloy steel(SA508 Gr.3) to Ni-Mo-Cr low alloy steel(SA508 Gr.4N). In this study, we evaluate the effects of alloying elements on the microstructural characteristics of Ni-Mo-Cr low alloy steel. The changes in the stable phase of the SA508 Gr.4N low alloy steel with alloying elements were evaluated by means of a thermodynamic calculation conducted with the software ThermoCalc. The changes were then compared with the observed microstructural results. The calculation of Ni-Mo-Cr low alloy steels confirms that the ferrite formation temperature decreases as the Ni content increases because of the austenite stabilization effect. Consequently, in the microscopic observation, the lath martensitic structure becomes finer as the Ni content increases. However, Ni does not affect the carbide phases such as M23C6 and M7C3. When the Cr content decreases, the carbide phases become unstable and carbide coarsening can be observed. With an increase in the Mo content, the M2C phase becomes stable instead of the M7C3 phase. This behavior is also observed in TEM. From the calculation results and the observation results of the microstructure, the thermodynamic calculation can be used to predict the precipitation behavior.
고분자전해필 연료전지 분리판용 316 스테인리스강의 전기전도도에 미치는 Nb, Ti 첨가 및 표면처리 효과
이석현(Lee, Seok-Hyun),김정헌(Kim, Jeong-Heon),김민철(Kim, Min-Chul),천동현(Chun, Dong-Hyun),위당문(Wee, Dang-Moon) 한국신재생에너지학회 2006 한국신재생에너지학회 학술대회논문집 Vol.2006 No.11
Nb and Ti were added to 316 stainless steel, and then heat-treatments and surface treatments were performed on the 316 stainless steel and the Nb- and Ti-added alloys. All samples indicated enhanced electrical conductivity after surface treatments, whereas they showed low electrical conductivity before surface treatments due to the existence of non-conductive passive film on the alloy surface. In particular, the Hb- and Ti-added alloys showed remarkable enhancement of electrical conductivity compared to the original alloy, 316 stainless steel. Surface characterization revealed that small carbide particles formed on the alloy surface after surface treatments, while the alloys indicated flat surface structure before surface treatments. Cr_{23}C<sub>6</sub> mainly formed on the 316 stainless steel, and NbC and TiC mainly formed on the Nb- and Ti-added alloys, respectively. We attribute the enhanced electrical conductivity after surface treatments to the formation of these carbide particles, possibly acting as a means of electro-conductive channel through the passive film. Furthermore, NbC and TiC are supposed to be more effective carbides than Cr_{23}C<sub>6</sub> as electro-conductive channels of stainless steel
Ni-Mo-Cr계 저합금강의 천이온도영역에서의 파괴인성에 미치는 Ni 및 Cr 함량의 영향
이기형 ( Ki Hyoung Lee ),박상규 ( Sang Gyu Park ),김민철 ( Min Chul Kim ),이봉상 ( Bong Sang Lee ),위당문 ( Dang Moon Wee ) 대한금속·재료학회 2009 대한금속·재료학회지 Vol.47 No.9
Materials used for a reactor pressure vessel(RPV) are required high strength and toughness, which determine the safety margin and life of a reactor. Ni-Mo-Cr low alloy steel shows better mechanical properties than existing RPV steels due to higher Ni and Cr contents compared to the existing RPV steels. The present study focuses on effects of Ni, Cr contents on the cleavage fracture toughness of Ni-Mo-Cr low alloy steels in the transition temperature region. The fracture toughness was characterized by a 3-point bend test of precracked Charpy V-notch(PCVN) specimens based on ASTM E1921-08. The test results indicated that the fracture toughness was considerably improved with an increase of Ni and Cr contents. Especially, control of Cr content was more effective in improving fracture toughness than manipulating Ni content, though Charpy impact toughness was changed more extensively by adjusting Ni content. These differences between changes in the fracture toughness and that in the impact toughness were derived from microstructural features, such as martensite lath size and carbide precipitation behavior.
논문 : 상변태 ; 금속간화합물 TiAl의 미세조직과 기계적 성질에 미치는 탄소 및 질소의 영향
윤주환 ( Jua Hwan Yun ),김민철 ( Min Chul Kim ),오명훈 ( Myung Hoon Oh ),이종탁 ( Chong Tak Lee ),위당문 ( Dang Moon Wee ) 대한금속재료학회 ( 구 대한금속학회 ) 1996 대한금속·재료학회지 Vol.34 No.11
Effects of carbon and nitrogen additions on microstructure and mechanical properties of Ti-48.5Al-1.5Mo (at.%) alloys were investigated. The alloys added with 0.3%, 1.0% and 2.0%C or N were prepared by vacuum arc melting, and heat-treated at 1390℃ for lamellar microstructure and then aged at 900℃. Tensile tests were performed in air with the strain rate of 2×10-4S-1 at room temperature and 800℃. It was found that C (or N) addition decreased the grain size of lamellar structure. Especially, 1.0%C(or N) and 2.0%C(or N) addition refined the grain size to 1/10 of that of the mother alloy. Only fine Ti3AlN precipitates were formed at the lamellar boundaries for the alloy containing 0.3% N, but Ti2AlN precipitates of a few micrometers in size were also formed in the matrix in addition to Ti3AlN precipitates for the alloys with 1.0 and 2.0% N. Tensile elongation at room temperature decreased markedly for the alloys with 0.3%C or N but recovered for the alloys with 1.0% and 2.0% addition compared to the value of the mother alloy. Yield strength at room temperature for the alloys containing 1.0% and 2.0% C or N increased up to two times of the value of the mother alloy, and the high strength was maintained up to 800℃. The aged alloys showed much higher tensile elongation at room temperature than the alloys only heat-treated to obtain the lamellar microstructure.