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니켈계 초내열합금 CM247LC의 일방향응고 시 미세조직 형성거동 분석
서성문 ( Seong Moon Seo ),정희원 ( Hi Won Jeong ),윤대원 ( Dae Won Yun ),안영근 ( Young Keun Ahn ),이재현 ( Je Hyun Lee ),유영수 ( Young Soo Yoo ) 한국주조공학회 2013 한국주조공학회지 Vol.33 No.5
The Ni-base superalloy CM247LC was directionally solidified (DS) using the Bridgman-type furnace to understand the effect of the chill plate on the microstructural evolution, such as dendrite arm spacing, microporosity, and MC-type carbide. The DS process was also modeled by the PROCAST to predict the solidification rate, thermal gradient, and resultant cooling rate in the entire length of the DS specimen. Due to the quenching effects of chill plate, four distinct areas were found to form in the specimen, in which the solidification rate was changed, during DS at a given withdrawal rate of 0.083 mm/s. Among the microstructural features investigated, the dendrite arm spacings and average size of the MC-type carbide near the chill plate were found to be influenced by the quenching effect of the chill plate. However, no significant influence was found on the size and volume fraction of microporosity, and the volume fraction of the MC-type carbide. The relationship between the microstructural features and the solidification variables was also analyzed and discussed on the basis of a combination of experimental and modeling results
니켈계 초내열합금의 응고 및 용질원소의 편석 거동에 미치는 레늄 및 루테늄 첨가의 영향
서성문 ( Seong Moon Seo ),정희원 ( Hi Won Jeong ),이재현 ( Je Hyun Lee ),유영수 ( Young Soo Yoo ),조창용 ( Chang Yong Jo ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.11
The influence of rhenium (Re) and ruthenium (Ru) addition on the solidification and solute redistribution behaviors in advanced experimental Ni-base superalloys has been investigated. A series of model alloys with different levels of Re and Ru were designed based on the composition of Ni-6Al-8Ta and were prepared by vacuum arc melting of pure metallic elements. In order to identify the influence of Re and Ru addition on the thermo-physical properties, differential scanning calorimetry analyses were carried out. The results showed that Re addition marginally increases the liquidus temperature of the alloy. However, the γ` solvus was significantly increased at a rate of 8.2℃/wt.% by the addition of Re. Ru addition, on the other hand, displayed a much weaker effect on the thermo-physical properties or even no effect at all. The microsegregation behavior of solute elements was also quantitatively estimated by an electron probe microanalysis on a sample quenched during directional solidification of primary γ with the planar solid/liquid interface. It was found that increasing the Re content gradually increases the microsegregation tendency of Re into the dendritic core and γ` forming elements, such as Al and Ta, into the interdendritic area. The strongest effect of Ru addition was found to be Re segregation. Increasing the Ru content up to 6 wt.% significantly alleviated the microsegregation of Re, which resulted in a decrease of Re accumulation in the dendritic core. The influence of Ru on the microstructural stability toward the topologically close-packed phase formation was discussed based on Scheil type calculations with experimentally determined microsegregation results.
Ni 기지 초내열합금의 고온산화 저항성에 미치는 Ti의 영향
박시준 ( Si-jun Park ),서성문 ( Seong-moon Seo ),유영수 ( Young-soo Yoo ),정희원 ( Hi-won Jeong ),장희진 ( Hee Jin Jang ) 한국부식방식학회 2016 Corrosion Science and Technology Vol.15 No.3
The effects of Ti on the high temperature oxidation of Ni-based superalloys were investigated by cyclic oxidation at 850 °C and 1000 °C. The oxide scale formed at 850 °C consists of Cr2O3, Al2O3, and NiCr2O4 layers, while a continuous Al2O3 layer was formed at 1000 °C. The oxidation rate of the alloy with higher Ti content was higher than the alloy with less Ti content at 850 °C, possibly due to the increase in the metal vacancy concentration in the Cr2O3 layer involved by incorporation of Ti4+. However, Ti improved the oxidation resistance of the superalloy at 1000 °C by reducing oxygen vacancy concentration in Al2O3 layer.
일방향 응고된 Co기 초내열합금 FSX-414의 응고속도에 따른 응고조직 및 편석 거동
이현정 ( Hyun Jung Lee ),이재현 ( Je Hyun Lee ),서성문 ( Seong Moon Seo ),조창용 ( Chang Young Jo ),권석환 ( Seok Hwan Gwon ),장병문 ( Byeong Moon Chang ) 대한금속재료학회 ( 구 대한금속학회 ) 2009 대한금속·재료학회지 Vol.47 No.7
Co base superalloys have been widely used for the parts of gas turbine due to their excellent strength, thermal fatigue, oxidation resistance and weldability at high temperature. In this study, directional solidifications were carried out at various solidification rates, including 0.5~300 μm/s in the Co base superalloy FSX-414. The cellular interface were formed at a low solidification rate, 1 μm/s, and the dendritic interface was found at higher solidification rates, 5~300 μm/s. As the spacing of dendrite structure decreased, the size and spacing of eutectics decreased. Dendrite arm spacing decreased with increasing solidification rates and temperature gradient. It was interesting to find the M23C6 eutectic microstructure formed between γ dendrites. Composition analysis showed that Cr and W were segregated severely between the dendrites, which resulted in the formation of Cr-rich M23C6 and W-rich MC carbides.
1Cr-1.25Mo-0.25V 강 잉곳의 응고편석 및 균질화 거동
김동배 ( Dong-bae Kim ),나영상 ( Young-sang Na ),서성문 ( Seong-moon Seo ),이재현 ( Je-hyun Lee ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.9
As a first step to optimizing the homogenization heat treatment following high temperature upset forging, the solidification segregation and the homogenization behaviors of solute elements were quantitatively analyzed for 1Cr-1.25Mo-0.25V steel ingot by electron probe micro-analysis (EPMA). The random sampling approach, which was designed to generate continuous compositional profiles of each solute element, was employed to clarify the segregation and homogenization behaviors. In addition, ingot castings of lab-scale and a 16-ton-sized 1Cr-1.25Mo-0.25V steel were simulated using the finite element method in three dimensions to understand the size effect of the ingot on the microsegregation and its reduction during the homogenization heat treatment. It was found that the microsegregation in a large-sized ingot was significantly reduced by the promotion of solid state diffusion due to the extremely low cooling rate. On the other hand, from the homogenization point of view, increasing the ingot size causes a dramatic increase in the dendrite arm spacing, and hence the homogenization of microsegregation in a large-sized ingot appears to be practically difficult.(Received November 18, 2015; Accepted March 17, 2016)
1Cr-1.25Mo-0.25V 합금강의 단조 전 균질화 처리에 따른 미세조직 변화 및 고온변형 안정성 평가
권거영 ( Keo Young Kwon ),나영상 ( Young Sang Na ),서성문 ( Seong Moon Seo ),양재규 ( Jea Kyu Yang ),김양도 ( Yang Do Kim ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.12
In order to investigate the effects of homogenization treatment on microstructural change and high temperature deformation stability, a series of hot compression tests and homogenization treatment were conducted for as-cast and upset-forged 1Cr-1.25Mo-0.25V steels. Microstructural inhomogeneity like dendritic morphology and elemental segregation in as-cast steel was homogenized after 10 hours-holding at 1200 ℃, followed by the rapid grain coarsening up to about 700 μm after 20 hours-holding. However, upset- forged steel showed rapid grain coarsening even in the early stage of high temperature holding at 1200 ℃. Compression tests for the 1Cr-1.25Mo-0.25V steels showed that flow stresses of as-cast 1Cr-1.25Mo-0.25V steel were higher than those of the upset-forged at temperatures lower than 1000 ℃. By analyzing the compression test results based on a dynamic materials model, we concluded that the microstructural inhomogeneity diminished hot deformation stability of the as-cast 1Cr-1.25Mo-0.25V steel. It is clear that the microstructural homogenization of as-solidified steel prior to upset forging is essential for improving the hot deformation stability and soundness of hot forgings.
박경미 ( Kyung Mi Park ),구지호 ( Ji Ho Gu ),서성문 ( Seong Moon Seo ),정희원 ( Hee Won Jeong ),신종호 ( Jong Ho Shin ),심권보 ( Kwon Bo Sim ),이재현 ( Je Hyun Lee ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.3
Directional solidification experiments were carried out on modified 9Cr1Mo steel and 10Cr1MoW steel to investigate their solidification and segregation characteristics. Under a given temperature gradient, both steels were solidified at the same growth rates of 1, 5, 50 and 100 μm/s, respectively. A detailed study of the solidification sequence for both steels revealed that delta ferrite was the leading phase and gamma austenite nucleated from the solid solidified earlier. A quick phase transformation of delta into gamma was made at growth rates faster than 50 μm/s. Therefore, almost all delta dendrites were identified as gamma phases to be transformed. On the other hand, compositional analyses performed on the solid/liquid interface confirmed that alloying elements in both steels were hardly segregated ahead of the solid/liquid interface. This appears to be responsible for a very narrow freezing range which suppresses elemental segregation.
CM247LC 초내열합금에서 일방향응고 스타트 블록의 초기 핵생성 조건에 따른 결정립 성장
윤혜영 ( Hye Young Yoon ),이재현 ( Je Hyun Lee ),정형민 ( Hyeong Min Jung ),서성문 ( Seong Moon Seo ),조창용 ( Chang Young Jo ),권석환 ( Seok Hwan Gwon ),장병문 ( Byeong Moon Chang ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.1
The grain size and growth direction of a directionally solidified turbine blade were evaluated by the initial nucleation condition at the start block of directional solidification. The initial nucleation condition was controlled by inserting a Ni foil on the directional solidification plate of the directional solidification furnace. Fine grains with good orientation were obtained in the faster cooling condition at the start block. The nucleus number was compared with the cooling rate of the start block by electron back scattered diffraction (EBSD). DSC (differential scanning calorimeter) analysis was performed to compare the melting point and undercooling for nucleation of the coarse nuclei and fine nuclei of the start block. The faster cooling condition at the start block showed more undercooling for nucleation and smaller size of nuclei which resulted in a fine grain with good orientation in the directional turbine blade.