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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

Title
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
Authors
Hong, SShin, SYLee, SKim, NJ
POSTECH Authors
Lee, SKim, NJ
Date Issued
Aug-2010
Publisher
KOREAN INST METALS MATERIALS
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
DWTT; metals; rolling; mechanical properties; impact test; PIPELINE STEELS; CARBON STEELS; MICROSTRUCTURES; BEHAVIOR
URI
http://oasis.postech.ac.kr/handle/2014.oak/25446
DOI
10.3365/KJMM.2010.48.08.705
ISSN
1738-8228
Article Type
Article
Citation
KOREAN JOURNAL OF METALS AND MATERIALS, vol. 48, no. 8, page. 705 - 716, 2010-08
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 LEE, SUNG HAK
Dept of Materials Science & Enginrg
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