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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.
염종택(J. T. Yeom),김지훈(J. H. Kim),김정한(J. H. Kim),홍재근(J. K. Hong),이재식(J. S. Lee) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
The hot forming process of a CAM for vessel engine was designed by finite element (FE) simulation and experimental analysis. An aim of process design was to achieve the near-net shaped CAM forgings by hot forging process. Based on the compression test results of the low alloy steel, deformation processing map was generated using the superposition approach between the dynamic materials model(DMM) and flow stability and/or instability criteria. From the processing map, the initial heating temperature was determined as 1200℃. FE analysis was simulated to predict the formation of rolling defects and deformed shape with different forging designs. Optimum process design suggested In this work was made by comparing with the CAM for vessel engine manufactured by actual forging process.
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.