Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
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Correlation Study of Microstructure and Mechanical Properties in Heat Affected Zones of API X80 Pipeline Steels containing Complex Oxides

복합산화물이 형성된 API X80 라인파이프강의 용접열영향부 미세조직과 기계적 특성의 상관관계 연구

  • Shin, Sang Yong (Center for Advanced Aerospace Materials Pohang University of Science and Technology) ;
  • Oh, Kyoungsik (Steelmaking 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) ;
  • 이성학 (포항공과대학교 항공재료연구센터)
  • Received : 2008.06.10
  • Published : 2009.02.25
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Abstract

This study is concerned with the correlation between microstructure and mechanical properties in heat affected zones (HAZs) of API X80 pipeline steels containing complex oxides. Three kinds of specimens were fabricated by varying alloying elements of Ti, Al, and Mg to form complex oxides, and their microstructures, Vickers hardness, Charpy impact properties were investigated. The number of complex oxides increased as the excess amount of Ti, Al, and Mg was included in the steels. The simulated HAZs containing a number of oxides showed a high volume fraction of acicular ferrite region because oxides acted as nucleation sites for acicular ferrite. According to the correlation study between thermal input, volume fraction of acicular ferrite region, and Charpy impact properties, the ductile fracture occurred predominantly when the volume fraction of acicular ferrite region was 65% or higher, and the Charpy absorbed energy was excellent over 200 J. When the volume fraction of acicular ferrite region was 35% or lower, the Charpy absorbed energy was poor below 50 J as the brittle cleavage fracture occurred. These findings suggested that the active nucleation of acicular ferrite in the oxide-containing steel HAZs was associated with the great improvement of Charpy impact properties of the HAZs.

Keywords

Acknowledgement

Supported by : 한국과학재단

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