Korean Journal of Materials Research (한국재료학회지)

Materials Research Society of Korea (한국재료학회)
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Effect of Molybdenum Addition and Specimen Orientation on Microstructure and Mechanical Properties of API X70 Linepipe Steels

Mo 첨가 및 시편 방향에 따른 API X70 라인파이프강의 미세조직과 기계적 특성

  • Dong-Kyu Oh (Department of Materials Science and Engineering, Seoul National University and Technology (SEOULTECH)) ;
  • Seung-Hyeok Shin (Department of Materials Science and Engineering, Seoul National University and Technology (SEOULTECH)) ;
  • Byoungchul Hwang (Department of Materials Science and Engineering, Seoul National University and Technology (SEOULTECH))
  • 오동규 (서울과학기술대학교 신소재공학과) ;
  • 신승혁 (서울과학기술대학교 신소재공학과) ;
  • 황병철 (서울과학기술대학교 신소재공학과)
  • Received : 2023.05.18
  • Accepted : 2023.06.19
  • Published : 2023.06.27
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Abstract

This study aims to examine the correlation between microstructures and the mechanical properties of two high-strength API X70 linepipe steels with different specimen directions and Moaddition. The microstructure of the Mo-added steel has an irregularly shaped AF, GB matrix with pearlite because of the relatively large deformation in the non-recrystallization temperature region, while that of the Mo-free steel shows a PF matrix with bainitic microstructure. In the Mo-added steel, the M/A (martensite-austenite) in granular bainite (GB) and pearlite act as crack initiation sites with decreased upper shelf energy and an increased ductile to brittle transition temperature (DBTT). Regardless of Mo addition, all of the steels demonstrate higher strength and lower elongation in the T direction than in the L direction because of the short dislocation glide path and ease of pile-up at grain boundaries. In addition, the impact test specimens with T-L direction had a lower impact absorbed energy and higher DBTT than those with the L-T direction because the former exhibit shorter unit crack path compared to the latter.

Keywords

Acknowledgement

The present study was supported by the Technology Innovation Program (Grant No. 20016064) through the Ministry of Trade, Industry and Energy (MOTIE), South Korea.

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