Effects of microstructure on inverse fracture occurring during drop-weight tear testing of high-toughness X70 pipeline steels |
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Authors: | Byoungchul Hwang Yang Gon Kim Sunghak Lee Nack J Kim Jang Yong Yoo |
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Affiliation: | (1) the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, 790-784 Pohang, Korea;(2) the Materials Science and Engineering Department, Pohang University of Science and Technology, Korea;(3) the Plate Research Group, Technical Research Laboratories, POSCO, 790-785 Pohang, Korea |
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Abstract: | The effects of microstructure on inverse fracture occurring in the hammer-impacted region were analyzed after conducting a
drop-weight tear test (DWTT) on high-toughness pipeline steels. Three kinds of steels were fabricated by varying the alloying
elements, and their microstructures were varied by the rolling conditions. The pressed-notch (PN) or chevron-notch (CN) DWTT
and Charpy V-notch (CVN) impact tests were conducted on the rolled steel specimens, and the results were discussed in comparison
with the data obtained from CVN tests of prestrained specimens. In the hammer-impacted region of the DWTT specimens, abnormal
inverse fracture having a cleavage fracture mode appeared, and the inverse fracture area correlated well with the upper-shelf
energy (USE) obtained from the CVN test and with the grain size. The steel specimens having a higher USE or having coarse
polygonal ferrite tended to have a larger inverse fracture area than those having a lower USE or having fine acicular ferrite.
This was because steels having a higher impact absorption energy required higher energy for fracture initiation and propagation
during the DWTT. These results were confirmed by the CVN data of prestrained steel specimens. |
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