Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
권호 표지

Effects of Complex Oxides on HAZ Toughness of Three API X80 Linepipe Steels

API X80 라인파이프강의 용접열영향부 충격인성에 미치는 복합산화물의 영향

  • Shin, Sang Yong (Center for Advanced Aerospace Materials Pohang University of Science and Technology) ;
  • Oh, Kyoungsik (Steelmaking Research Group Technical Research Laboratories, POSCO) ;
  • Kang, Ki Bong (Plate Research Group Technical Research Laboratories, POSCO) ;
  • Lee, Sunghak (Center for Advanced Aerospace Materials Pohang University of Science and Technology)
  • 신상용 (포항공과대학교 항공재료연구센터) ;
  • 오경식 (POSCO 기술연구소 제강연구그룹) ;
  • 강기봉 (POSCO 기술연구소 후판연구그룹) ;
  • 이성학 (포항공과대학교 항공재료연구센터)
  • Received : 2007.10.11
  • Published : 2008.04.22
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Abstract

This study is concerned with effects of complex oxides on Charpy impact toughness of heat affected zone (HAZ) of API X80 linepipe steels. Three kinds of steels were fabricated by varying alloying elements such as Ti, Al, and Mg and hot-rolling conditions to form complex oxides, and their microstructures and Charpy impact properties were investigated. The number of complex oxides present in the steel containing excess Ti, Al, and Mg was twice larger than that in the conventional steels, while their size ranged from 1 to $3{\mu}m$ in the three steels. After the HAZ simulation test, the steel containing a number of oxides contained about 20 vol.% of acicular ferrite in the simulated HAZ, together with bainitic ferrite and martensite, whereas the HAZ microstructure of the conventional steels consisted of bainitic ferrite and martensite with a small amount of acicular ferrite. This formation of acicular ferrite in the oxide-containing steel was associated with the nucleation of acicular ferrite at complex oxides, thereby leading to the great (five times or more) improvement of Charpy impact toughness over the conventional steels.

Keywords

Acknowledgement

Supported by : POSCO, 한국과학재단

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