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주조용 이상스테인리스강에서 응고속도 및 질소고용도에 따른 오스테나이트 석출 거동
이종엽,이재현,김상식,최병학,김성준,손희영,Lee, Jong-Yeop,Lee, Je-Hyun,Kim, Sang-Sik,Choi, Byung-Hak,Kim, Sung-Jun,Son, Hee-Young 한국재료학회 2007 한국재료학회지 Vol.17 No.12
Austenite precipitation behavior was studied with solidification rates and alloying contents, N and Cr, in duplex stainless steels by directional solidification. Directional solidification experiments were carried out with solidification rates, $1{\sim}100mm/s$, and N and Cr contents, $0{\sim}0.27wt.%,\;25{\sim}28wt.%$ respectively, in a duplex stainless steel, CD4MCU. As the solidification rate increases, the dendrite spacing reduced and the austenite phase in the ferrite matrix became finer. The volume fraction of austenite phase increased and its shape went to be round with increasing nitrogen contents in duplex stainless alloys. The Cr alloying element, even though it is a ferrite former, showed to enhance the nitrogen solubility in the alloy and caused the austenite round and finer. Also, Cr was supposed to decrease the austenite volume fraction, but it increased the austenite slightly due to increasing nitrogen solubility during solidification.
이재현,조용성,강수현,박장식,김상식 ( Je Hyun Lee,Yong Seong Cho,Soo Hyeon Kang,Jang Sik Park,Sang Sik Kim ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.1
N/A There has been a considerable interest to develop the silicide alloys as high temperature structural materials because of their excellent high temperature stability and strength, however, their lack of room temperature ductility and toughness was a main obstacle for the application. In order to improve ductility while maintaining good high temperature properties, possible refractory metal-silicide eutectic alloys composed of fine two phases were prepared by VAR(Vacuum Arc Remelting). Three silicide alloys, Nb-Nb₃Si, Ti-Ti_5Si₃, V-V₃Si, were selected as prospecting silicide eutectics and those high temperature characteristics were evaluated by high temperature compression test.
선형회귀분석법을 통한 주조용 A356 합금의 인장특성에 미치는 미세조직적 인자의 영향
홍성진 ( Seong Jin Hong ),김상식 ( Sang Shik Kim ),이재현 ( Je Hyun Lee ),권용남 ( Yong Nam Kwon ),이영선 ( Young Seon Lee ),이정환 ( Jung Hwan Lee ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 대한금속·재료학회지 Vol.44 No.8
The effects of microstructural variables, including DAS (dendrite arm spacing), the size of primary a phase, the size of eutectic Si particle and the thickness of eutectic structure, on tensile behavior of A356 cast aluminum alloy were quantitatively identified using linear regression analysis method. For systematic microstructural control in A356 alloy, directional solidification method was used with different solidification rates of 5, 25, 50 and 100 ㎛/s, respectively. The linear regression analysis suggests that both DAS and the size of primary a phase dominantly affect tensile strength of A356 cast aluminum alloy, while tensile ductility is most strongly dependent on the thickness of eutectic structure. The change in tensile behavior with varying microstructural variables in A356 alloy is discussed based on fracto graphic and micrographic observations.
SM45C 강의 narrow gap 용접부 회전굽힘 피로 특성
한승전 ( Seung Zeon Han ),안지혁 ( Jee Hyuk Ahn ),이재현 ( Je Hyun Lee ),김상식 ( Sang Shik Kim ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.11
SM45C steel was welded by conventional CO2 arc and narrow gap welding (NGW). The fatigue strength of NGWed sample had a value about 90 MPa higher than that of the CO2 arc welded sample. The width of welding and heat affected zone in NGWed samples decreased about 40% compared to the conventional CO2 arc welded sample. The hardness value of the welding zone in the NGW sample was 33.3% higher than that of the CO2 arc welded sample. The microstructure change of the SM45C during NGW revealed that the matrix was transformed to the martensite phase. With the small width of welding and heat affected zone in the NGW, therefore, the specimen with NGW had a faster cooling rate after welding. We therefore concluded that the hardness was increased by hard martensite formation during cooling after NGW, and this increase in hardness resulted in better fatigue strength of SM45C steel compared to conventional CO2 arc welding. (Received March 13, 2014)
주조용 CD4MCU 이상 스테인리스강의 Mo 첨가에 따른 인장 및 부식 거동
장영환,손진일,김상식,이재현 대한금속재료학회 2005 대한금속·재료학회지 Vol.43 No.3
In the present study, the effect of Mo contents on the microstructure, tensile and corrosion behaviors of as-solutionized CD4MCU cast duplex stainless steel was examined. The polarization test was conducted in 3.5% NaCl +5% H₂SO_(4) aqueous solution for general corrosion resistance and the slow strain rate tests were also conducted in air and 3.5% NaC1+5% H₂SO_(4) aqueous solution to study the stress corrosion cracking (SCC) of the present alloy. A substantial microstructural evolution of CD4MCU cast duplex stainless steel was observed with different Mo contents, which in turn affected the tensile and corrosion behaviors significantly. The beneficial effect of Mo on improving the corrosion and the SCC resistances was largely overwhelmed by this variation of microstructural characteristics. The relationship between the microstructural evolution and the tensile and corrosion behavior of CD4MCU cast duplex stainless steels with different Mo contents was discussed based on the optical and SEM micrographic and fractographic observations. (Received September 2, 2004)
열처리조건에 따른η상의 석출이 IN792+Hf 합금의 기계적 특성에 미치는 영향에 관한 연구
조창용,최승주,이재현,서성문,김상식 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.10
Effects of different heat treatment conditions on the microstructure and mechanical properties of IN792+Hf alloy were examined. IN792+Hf alloy with standard heat treatment showed a considerable amount of platelet η phases in the interdendritic regions, which acts as sources of secondary cracks. In order to eliminate the detrimental η phases, solution heat treatment was performed at higher temperature and for longer time. IN792+Hf with solution treatment at 1200℃ for 5 hours did not exhibit any η phases, and showed improved yield strength at elevated temperatures. However, the tensile ductility, as represented by %elongation, was reduced, which is believed to be due to the grain growth and coarse MC carbide formation during solution heat treatment.
Rene' 77 합금의 고온 응력- 파단에 따른 σ 상의 생성 및 미세조직의 변화
조창용,최승주,이재현,염종택,김상식 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.10
The possibility of formation of the a phase in the Rene´ 77 superalloy, when exposed to high temperature: and under the applied stress, has been evaluated. The Phacomp calculations on the Rene´ 77 used in the present study indicates that an electron vacancy number of this alloy is 2.45, which is not immune to formation of the a phase. Among the four stress-rupture test conditions, the σ phase was observed when the sample was exposed at 871℃ under the applied stress of 276 ㎫. The shape of the σ phase observed in the present study was more-or-less close to blocky shape, and the detrimental effect on stress-rupture property of the Rene´ 77 was minimal. It was interesting to find that the fracture modes were different with stress conditions. While fracture initiated near the carbide in High stress condition, it appeared to grow near the grain boundary or triple point in low stress condition.