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The Effect of Thermal Exposure on the Microstructural Evolution and Tensile Properties in Cast Hastelloy X

Hastelloy X 주조재의 열간 노출에 따른 미세조직 및 인장 특성 변화

  • Choi, Baig Gyu (High Temperature Materials Department, Korea Institute of Materials Science) ;
  • Kim, In Soo (High Temperature Materials Department, Korea Institute of Materials Science) ;
  • Do, Jeonghyeon (High Temperature Materials Department, Korea Institute of Materials Science) ;
  • Jung, Joong Eun (High Temperature Materials Department, Korea Institute of Materials Science) ;
  • Jung, In Yong (High Temperature Materials Department, Korea Institute of Materials Science) ;
  • Hong, Hyun Uk (Department of Materials Science and Engineering, Chanagwon National University) ;
  • Jo, Chang Yong (High Temperature Materials Department, Korea Institute of Materials Science)
  • 최백규 (재료연구소 내열재료연구실) ;
  • 김인수 (재료연구소 내열재료연구실) ;
  • 도정현 (재료연구소 내열재료연구실) ;
  • 정중은 (재료연구소 내열재료연구실) ;
  • 정인용 (재료연구소 내열재료연구실) ;
  • 홍현욱 (창원대학교 신소재공학부) ;
  • 조창용 (재료연구소 내열재료연구실)
  • Received : 2017.08.10
  • Accepted : 2017.09.25
  • Published : 2017.10.31

Abstract

Microstructural evolution of cast Hastelloy X during thermal exposure has been investigated. OM, SEM, and TEM microscopy were carried out on the as-cast, the standard heat treated, and the thermally exposed conditions. Tensile tests were also conducted to understand the effect of microstructural evolution on the degradation of tensile properties. Coarse $M_6C$ and fine $M_{23}C_6$ carbides were found in as-cast Hastelloy X with fine carbides on sub-boundary. Some of $M_{23}C_6$ carbide dissolved into the matrix during solution heat treatment and dislocation network formed at the interface between the carbide and the matrix due to the misfit strain. There was no significant microstructural difference between the exposed specimens at $400^{\circ}C$ and the solution heat treated specimen. A large amount of $M_{23}C_6$ carbides precipitated along and near grain boundaries and sub-boundaries after exposure at $650^{\circ}C$. Exposure at $870^{\circ}C$ of the alloy caused precipitation of $M_6C$ and ${\mu}$. The strength increased and the elongation decreased by thermal exposure at $650^{\circ}C$ and $870^{\circ}C$ because carbides interfere with the movement of the dislocation. It was found that the precipitation of carbide gave significant effects on the tensile properties of Hastelloy X.

Keywords

References

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