Page 1 [ ] J. Kor. Inst. Met. & Mater. Vol. 41, No. 5 (2003) - 279

  

[ ] J. Kor. Inst. Met. & Mater. Vol. 41, No. 5 (2003)


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Analysis of Abnormal Fracture Appearance in Drop-Weight Tear Test of a High-Toughness Line-Pipe Steel Byoungchul Hwang, Sunghak Lee, Young Min Kim, Nack J. Kim, Jang Yong Yoo* and Chong Soo Woo* Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784, Korea *Plate, Rod & Welding Research Group, Technical Research Laboratories, POSCO, Pohang 790-785, Korea Abstract : In this study, various types of drop-weight tear test (DWTT) were conducted on a high-toughness linepipe steel in order to investigate abnormal fracture appearance occurring in the region impacted by a hammer. A pressed notch or a chevron notch was introduced into DWTT specimens, some of which had a back slot designed to decrease the inverse fracture area. After the DWTT, percent shear area, 85% shear appearance transition temperature, area of inverse fracture surface, hardness and work hardening exponent of the hammer-impacted region were measured. The results indicated that the shear area of the pressed notch DWTT specimens was larger than that of chevron notch DWTT specimens. In the hammer-impacted region of all the DWTT specimens, abnormal inverse fracture having a cleavage fracture mode appeared, and its area fraction was correlated well with Vickers hardness and work hardening exponent (n) measured by an indentation test. The formation of this inverse cleavage fracture raised the fracture propagation transition temperature by decreasing the shear area measured in accordance of the API 5L3 specification, which was confirmed by relating to the Charpy V-notch test data of pre-strained steel specimens. (Received January 23, 2003) Key words : High-toughness pipeline steel, Abnormal fracture appearance, Drop-weight tear test (DWTT), API 5L3 specification, Acicular ferrite


 




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