Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
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Separation Phenomenon Occurring during Charpy Impact test of API X80 Linepipe Steels

API X80 라인파이프강의 샤르피 충격 시험 시 발생하는 파열 현상 연구

  • Shin, Sang Yong (Center for Advanced Aerospace Materials, Pohang University of Science and Technology) ;
  • Hong, Suckmin (Center for Advanced Aerospace Materials, Pohang University of Science and Technology) ;
  • Bae, Jin-ho (Sheet Products & Process Research Group, Technical Research Laboratories, POSCO) ;
  • Kim, Kisoo (Sheet Products & Process Research Group, Technical Research Laboratories, POSCO) ;
  • Lee, Sunghak (Center for Advanced Aerospace Materials, Pohang University of Science and Technology)
  • 신상용 (포항공과대학교 항공재료연구센터) ;
  • 홍석민 (포항공과대학교 항공재료연구센터) ;
  • 배진호 (POSCO 기술연구소 박판연구그룹) ;
  • 김기수 (POSCO 기술연구소 박판연구그룹) ;
  • 이성학 (포항공과대학교 항공재료연구센터)
  • Received : 2008.10.13
  • Published : 2009.03.25
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Abstract

In this study, microstructural investigation was conducted on the separation phenomenon occurring during Charpy impact tests of API X80 linepipe steels. Particular emphasis was placed on the role of microstructural phases present in the API X80 steels such as acicular ferrite, bainite, and hard secondary phases. Detailed microstructural analysis of fractured impact specimens showed that highly elongated bainite worked as prior initiation sites for separations, and that the number and length of separations increased with increasing volume fraction of bainite. In the steels having high work hardenability, tearing-shaped separations were found because the hammer-impacted region was seriously hardened during the impact test, which led to the reduction in the impact toughness. As the test temperature decreased, the tendency of separations increased, but separations were not observed when the cleavage fracture prevailed at very low temperatures. Thus, the minimization of the formation of bainite and secondary phases in the steels would be beneficial for preventing or minimizing separations because separations deteriorated low-temperature impact toughness.

Keywords

Acknowledgement

Supported by : 한국과학재단

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