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중력주조 및 직접가압주조 7XXX 계 Al 합금의 미세조직에 관한 연구
김석원(Sug Won Kim),김대영(Dae Young Kim),우기도(Ki Do Woo),김동건(Dong Kun Kim) 한국주조공학회 1999 한국주조공학회지 Vol.19 No.1
N/A Squeeze casting process has been used in the field of a commercial manufacturing method, in which metal is enforcedly solidified under pressure enough to prevent the cast defects such as either gas porosity or shrinkage defect. In this paper, to clarify the relationship between applied pressures and macro·microstructural behaviors in gravity and direct squeeze casts, specimens were cast by various squeezing pressures during solidification of 7000 series Al wrought alloy in the metal die designed specially. The applied pressures used in this study were 0, 25, 50, and 75 MPa. The microstructural morphologies of squeeze cast were more fine and dense with increasing the applied pressures, because of the greater solidification rate of billet resulting from the applied pressure. A normal segregation phenomenon of an increasing in amount of eutectics towards the center of the billet was observed for squeeze casts, whereas gravity cast showed an inverse segregation phenomenon of an increasing in amount of eutectics towards the edge in the billet. This change in segregation pattern which is normal or inverse is due to a higher radial temperature gradient and reduced time in the semi solid state for squeeze casting. (Received September 2, 1999)
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대학 교육과정 지원 방안 모색을 위한 대학 교육과정 편성·운영의 문제점 분석
김대영 ( Dae Young Kim ),신원석 ( Won Sug Shi ),박인우 ( Inn Woo Park ) 안암교육학회 2014 한국교육학연구 Vol.20 No.2
본 연구는 국내 고등 교육기관의 교육과정 편성·운영에 대한 질적·양적 자료를 수집·분석함으로써 교육과정 편성·운영의 문제점을 파악하고 고등 교육의 질적 제고를 도모할 수 있는 교육과정 지원방안을 제안하고자 하는 목적을 가지고 있다. 이러한 목적을 달성하기 위해 교육과정 편성·운영 실무를 담당하고 있는 교수와 학사행정관리자들 대상으로 포커스 그룹 인터뷰(FGI)를 실시함으로써 내부자의 관점에서 교육과정 편성·운영 과정을 파악하고자 하였다. 또한 FGI 분석결과를 토대로 설문 문항을 개발하여 전국 4년제 대학에서 근무하는 교수와 학사행정관리자들에게 설문조사를 실시하였다. 설문분석 결과는 대체적으로 학사행정관리자들에 비해 교수들이 교육과정 관련 문제점을 더욱 심각하게 인식하고 있는 것으로 조사되었으며, 이러한 문제점을 해결하기 위해 교수와 학사행정관리자 모두 교육과정 연구 및 개편의 전담조직 및 인력 확충, 평가결과의 반영, 교육과정 편성·운영 관련 DB 구축, 정부의 재정적 지원 등의 필요성을 인식하고 있는 것으로 조사되었다. This study was to examine the problems of college curriculum organization and management and propose curriculum supporting system to enhance educational quality in higher education system in South Korea by collecting and analyzing the qualitative and quantitative data on college curriculum. For the study, focus group interview (FGI) was performed to gather information from the person in charge of curriculum organization and management in college. Based on the results of FGI, the survey instrument was developed and distributed to faculties and administrative staffs. The results showed that faculties took the problems on college curriculum more seriously. Also, both faculties and administrative staffs perceived the necessities of improvement of curriculum organization and management process such as expansion of college curriculum research team, reflection of the result of university assessment, establishment of curriculum database through the nation, and financial support from government.
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우기도,김석원,김대영,박영구,류재화 ( Kee Do Woo,Sug Won Kim,Dae Young Kim,Young Koo Park,Jae Hwa Ryu ) 한국열처리공학회 1997 熱處理工學會誌 Vol.10 No.2
In high carbon steels, the cementite phase is more unstable thermally than graphite, and it can lead to a marked deterioration in the formability. Many studies have been carried out to evaluate the effect of the fundamental elements on the graphitization of cementite in high carbon steels. In this present work, the effect of Mn, Cr addition on graphitization in Fe-0.65%C-1.0%Si steel has been investigated by means of hardness testing, optical microscopy and EPMA. The nucleation of graphite may mostly depend on the dissolution rate of cementite into ferrite and the number of the nucleation sites of graphite. The graphitization was promoted by the addition of 0.1%Mn in high carbon steel, but retarded by more addition than 0.5% of Mn. By the more addition of Cr than 0.1%, the graphitization of high carbon steel was strongly retarded. Because Mn was moderate anti-graphitizer, but Cr was stroug antigraphitizer.
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고온 내산화성 고 Si , Mo 구상흑연주철의 특성에 관한 연구
김석원,우기도,한상원,김정규,김대영 ( Sug Won Kim,Kee Do Woo,Sang Won Han,Jung Ku Kim,Dae Yong Kim ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.2
N/A The physical and chemical characteristics of Ductile Cast Iron(DCI) have been well known because of many studies about DCI. So it has a wide application in the field of heavy and automobile industry because DCI has a good combination of excellent castability and good mechanical properties. But its usage has been often restricted to use in parts such as exhaust manifold required high heat resistance in automobile industry. So, in this study, in order to achieve high heat resistance in DCI, DCI with addition of high Si and Mo alloy elements have been researched on mechanical properties, including heat resistances systematically. With the increase of Mo and Si content, the size and number of graphite in matrix of DCI increased and the pearlite in DCI matrix is transferred to ferrite because of Si strong former of ferrite, otherwhile carbide in matrix increased because of Mo carbide former. In the test of oxidation property, Si and Mo played an important role to retard oxidation of DCI. By the: addition of Si and Mo, the Charpy impact energy was decreased, whereas the total hardness was increased. (Received February 20, 1998)
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직접가압주조 7000 Al 합금의 열처리 특성에 관한 연구
김완기,김동건,김대영,김석원,우기도 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.10
The 7000 series, Al-Zn-Mg and Al-Zn-Mg-Cu aluminium alloys have been known to be strengthened by precipitation hardening with aging treatment. But, among of defects in 7000 Al alloy, casts defects such as gas porosity and shrinkage defect are formed during solidification because of wide mushy zone. This study was undertaken to investigate the effects of applied pressures on aging precipitating behavior, micro and macro-structures and mechanical properties in 7000 series Al alloys. The microstructure of 25, 50, 75 MPa specimens was more fine and dense than that of non-pressurized cast, because of the greater cooling rate of billet by the application of pressure. GP zone solvus was estimated to be 130℃ by DSC results. Growth of precipitates at 180℃ aging treatment was faster than 120℃ aging treatment. Hardness values of as cast specimens was increased by fine grain size and increase in solute amount within matrix with increase in applied pressure. In case of 180℃ aging treatment, aging time obtained highest hardness valuers was shortened than in case of 120℃ aging treatment. In case of 120℃ aging treatment, tensile strength and hardness was represented a similar increasing tendency. Due to fine grain size, tensile strength values of 7075 Al alloy was higher than that of 7050 Al alloy.
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