Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
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Effects of Specimen Thickness and Notch Shape on Fracture Mode Appearing in Drop Weight Tear Test (DWTT) Specimens of API X70 and X80 Linepipe Steels

API X70 및 X80 라인파이프강의 DWTT 시편 파괴 형태에 미치는 시편 두께와 노치 형태의 영향

  • Hong, Seokmin (Center for Advanced Aerospace Materials, Pohang University of Science and Technology) ;
  • Shin, Sang Yong (Center for Advanced Aerospace Materials, Pohang University of Science and Technology) ;
  • Lee, Sunghak (Center for Advanced Aerospace Materials, Pohang University of Science and Technology) ;
  • Kim, Nack J. (Graduate Institute of Ferrous Technology, Pohang University of Science and Technology)
  • 홍석민 (포항공과대학교 항공재료연구센터) ;
  • 신상용 (포항공과대학교 항공재료연구센터) ;
  • 이성학 (포항공과대학교 항공재료연구센터) ;
  • 김낙준 (포항공과대학교 철강대학원)
  • Received : 2010.02.03
  • Published : 2010.08.22
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Abstract

Effects of specimen thickness and notch shape on fracture mode appearing in drop weight tear test (DWTT) specimens of API X70 and X80 linepipe steels were investigated. Detailed microstructural analysis of fractured DWTT specimens showed that the fractures were initiated in normal cleavage mode near the specimen notch, and that some separations were observed at the center of the fracture surfaces. The Chevron-notch (CN) DWTT specimens had broader normal cleavage surfaces than the pressed-notch (PN) DWTT specimens. Larger inverse fracture surfaces appeared in the PN DWTT specimens because of the higher fracture initiation energy at the notch and the higher strain hardening in the hammer-impacted region. The number and length of separations were larger in the CN DWTT specimens than in the PN DWTT specimens, and increased with increasing specimen thickness due to the plane strain condition effect. As the test temperature decreased, the tendency to separations increased, but separations were not found when the cleavage fracture prevailed at very low temperatures. The DWTT test results, such as upper shelf energy and energy transition temperature, were discussed in relation with microstructures and fracture modes including cleavage fracture, shear fracture, inverse fracture, and separations.

Keywords

References

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