미세조직 변화를 고려한 대형 배기밸브 스핀들 제조공정 해석 = A Manufacturing Process analysis of Large Exhaust Valve Spindle considering Microstructure Evolution

다국어 초록 (Multilingual Abstract)

The microstructure evolution in hot forging process is composed of dynamic recrystallization during deformation as well as grain growth during dwell time. Therefore, the control of forging parameters such as strain, strain rate. temperature and holding time is important because the microstructure change in hot working affects the mechanical properties. Modeling equations are developed to represent the flow curve. grain size. recrystallized volume fraction and grain growth phenomena by various tests. The developed modeling equations were combined with thermo-viscoplastic finite element modeling to predict the microstructure change evolution during hot forging process. The large exhaust valve spindle (head diameter of 512mm) was simulated by closed die forging with hydraulic press and cooled in air after forging. The preform was heated to each 1080 and 1150$^{\circ}C$. Numerical calculation was performed by DEFORM-2D. a commercial finite element code. Heat transfer can be coupled with the deformation analysis in a non-isothermal deformation analysis. In order to obtain the fine and homogeneous microstructure and good mechanical properties in forging. the FEM would become a useful tool in the simulation of the microstructure development. In forging, appropriate temperature, strain and strain rate and rapid cooling are required to obtain the fine grain microstructure The optimal forging temperature and effective strain range of Nimonic 80A for large exhaust valve spindle are about 1080$\∼$l120$^{\circ}C$ and 150$\∼$200$\%$.

참고문헌 (Reference)

1 "해머 단조된 Alloy 718 디스크의 결정립 분포 해석" 6 (6): 250-256, 1997

2 "초내열합금 Nimonic 80A의 미세조직 변화에 대한 연구" 174-177, 2004

3 "전기 업셋팅 가공시의 열탄소성 해석에 관한 연구" 18 : 423-430, 1994.

4 "유한요소법을 이용한 단조공정시 조직예측기법의 적용 사례" 2001

5 "유한요소법을 이용한 Inconel 718의 열간단조공정시 동적 재결정거동 예측" 35 (35): 197-206, 1998

6 "배원병"금형강의 동적 및 정적 재결정 거동과 미세조직 변화 예측에 관한 연구" 10 : 338-346, 2001

7 "로워암 커넥터 열간단조 공정의 유한요소해석 및 미세조직 예측" 27 (27): 1243-1250, 2003

8 "Nickel-base superalloy forging for gas turbine applications: Process model, microstructural model and validation" metalforming2000

9 "Modeling the dynamic recrystallization under multi-stage hot deformation" me 52 : 4659-4668, 2004

10 "Micro- structure evolution during metal forming processes" me 28 : 563-573, 2003.

11 "Hot working characteristics of nimonic 75 Journal of Materials Processing Technology" 51 : 171-192, 1995

12 "Hot forging of a nickel-base superalloy, Journal of Materials Pro- cessing Technology" 98-102, 2001.

13 "Application of nimonic 80A to the forging of an exhaust valve head" 113 : 148-152, 2001.

14 "A study of the hot deformation behaviour and dynamic recrystallza- tion of Al-5wt.%Mg alloy" 118 : 356-361, 2001.