# 단조용 초내열 718 합금의 고온 변형 거동

• Na, Y.S. (Department of Materials Engineering, Korea Institute of Machinery and Materials) ;
• Choe, S.J. (Department of Materials Engineering, Korea Institute of Machinery and Materials) ;
• Kim, H.M. (Department of Materials Engineering, Korea Institute of Machinery and Materials)
• 나영상 (한국기계연구원 재료기술연구부) ;
• 최승주 (한국기계연구원 재료기술연구부) ;
• 김학민 (한국기계연구원 재료기술연구부)
In order to understand the high temperature deformation behavior of superalloy 718, a rotating grade 718 alloy has been compression tested to about 0.7 upset ratio at $927{\sim}1066^{\circ}C$ temperature range and $5{\times}10^{-4}{\sim}5{\times}10^0sec^{-1}$ strain rate. The maximum flow stress was increased with increasing strain rate, and similar behavior was observed with decreasing temperature. At low temperature and high strain rates other than $5{\times}10^{-1}sec^{-1}$, strain softening was occurred mainly by dynamic recovery and deformation twinning processes, while at high temperature and low strain rates strain softening was offseted by dynamic recrystallization. At $5{\times}10^{-1}sec^{-1}$, strain hardening was occurred due to work hardening of the dynamic recrystallized grains. Strain rate sensitivity, m, was varied with strain rates. In the case of lower strain rate tests, m was measured as 0.3 and it was observed that the deformation was mainly controlled by dynamic recrystallization. At higher strain rate, m was lowered to 0.1 and the deformation was controlled by the dynamic recovery and the deformation twinning processes.