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Ti-6Al-4V합금의 열간 후방압출에 대한 성형 안정성 평가모델의 고찰
염종택,박노광,이유환,신태진,황상무,홍성석,심인옥,이종수,Yeom Jong-Taek,Park Nho-Kwang,Lee You-Hwan,Shin Tae-Jin,Hwang Sang-Mu,Hong Sung-Suk,Shim In-Ok,Lee Chong-Soo 한국군사과학기술학회 2004 한국군사과학기술학회지 Vol.7 No.3
The metal forming behavior of Ti-6Al-4V tube during hot backward extrusion was investigated with various forming stabilities or instabilities criteria. that is, Ziegler's instability criterion, dynamic materials model(DMM) stability criteria and Rao's instability criterion. These approaches also were coupled to the internal variables generated from FE simulation. In order to validate the reliabilities of three criteria, hot backward extrusions for Ti-6Al-4V tube making were carried out with different backward extrusion designs. The useful model for predicting the forming defects was suggested through the comparison between experimental observations and simulation results.
Waspaloy 터빈디스크의 열간 단조시 결정립분포 해석에 관한 연구
염종택,이종수,김정한,이동근,박노광,Yeom, Jong-Taek,Lee, Chong-Soo,Kim, Jeoung-Han,Lee, Dong-Geun,Park, Nho-Kwang 한국군사과학기술학회 2006 한국군사과학기술학회지 Vol.9 No.2
The microstructure evolution during a hot forging of Waspaloy was investigated using the recrystallization model and FEM simulation. In order to obtain an uniform microstructure, hot forging was carried out by two step. The change of grain size during hot forging has a deep connection with dynamic recrystallization behavior. Avrami-type constitutive equation for the dynamic recrystallization was implemented into an user subroutine of 2D FE simulator. The evolution of grain structure in the two-step forging of Waspaloy was simulated using the 2D FEM user-subroutine. The detailed variation of microstructures due to dynamic recrystallization could effectively be predicted at various locations in a forged pancake.
재결정 및 결정립 성장거동을 기초한 조직예측 모델에 대한 변수 결정방법
염종택(J. T. Yeom),김정한(J. H. Kim),홍재근(J. K. Hong),박노광(N. K. Park) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
This work describes a method of determining material parameters included in recrystallization and grain growth models. Focus is on the recrystallization and grain growth models of Ni-Fe base superalloy, Alloy 718. High temperature compression tests at different strain, strain rate and temperature conditions were chosen to determine the material parameters of dynamic recrystallization model. The critical strain and dynamically recrystallized grain size and fraction at various process variables were quantitated with the microstructual analysis and strain-stress relationships of the compression tests. Besides, isothermal heat treatments were utilized to fit the material constants included in the grain growth model. Verification of the determined material parameters is carried out by comparing the measured data obtained from other compression tests.
선박용 과급기 로터 접합체(Alloy713LC-AISI 4140)의 이종 마찰용접
염종택(J. T. Yeom),홍재근(J. K. Hong),김정한(J. H. Kim),박노광(N. K. Park),박진형(J. H. Park),김종기(J. K. Kim) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
In this work, dissimilar friction welding of turbocharger rotor assembly composed of Alloy 713LC and AISI 4140 was designed with process variables. Process variables of the friction welding were investigated with initial sample shape, friction pressure and time. The quality of welded joins was tested by applying bending stresses in an appropriate jig. Microstructures of the friction welded samples were analyzed with micro-hardness tests and SEMIEDS. FE simulation was carried out to investigate the effect of welding variables in friction welding process on the distributions of the state variables such as strain, strain rate and temperature. The temperature distribution in the heat-affected zone obtained from FE simulation provided a greater understanding of the microstructure evolution during friction welding.
염종택(J. T. Yeom),김정한(J. H. Kim),홍재근(J. K. Hong),박노광(N. K. Park) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
As a class of materials, Ni-base superalloys are among the most difficult metal alloys to forget together with refractory metals and cobalt-base superalloys. The mechanical properties of Ni-base superalloys depend very much on grain size and the strengthening phases, γ"(Ni₃(Al,Ti)-type) and γ".(Ni₃Nb-type). Especially, the control of grain size remains as a sole means for the control of mechanical properties. The grain size and distribution changes of the wrought superalloys during hot working and heat treatment are mainly controlled by the recrystallization and grain growth behaviors. In this presentation, prediction technology of grain size through the computer-aided process design, and numerical modeling for predicting the microstructure evolution of Ni-base superalloy during hot working were introduced. Also, some case studies were dealt with actual forming processes of Ni-base superalloys.