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Vol.47, No.3, 155 ~ 169, 2009
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| Title |
| Separation Phenomenon Occurring during Charpy Impact test of API X80 Linepipe Steels |
| 김기수 Ki Soo Kim , 배진호 Jin Ho Bae , 이성학 Sung Hak Lee , 신상용 Sang Yong Shin , 홍석민 Suck Min Hong |
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| Abstract |
| In this study, microstructural investigation was conducted on the separation phenomenon occurring during Charpy impact tests of API X80 linepipe steels. Particular emphasis was placed on the role of microstructural phases present in the API X80 steels such as acicular ferrite, bainite, and hard secondary phases. Detailed microstructural analysis of fractured impact specimens showed that highly elongated bainite worked as prior initiation sites for separations, and that the number and length of separations increased with increasing volume fraction of bainite. In the steels having high work hardenability, tearing-shaped separations were found because the hammer-impacted region was seriously hardened during the impact test, which led to the reduction in the impact toughness. As the test temperature decreased, the tendency of separations increased, but separations were not observed when the cleavage fracture prevailed at very low temperatures. Thus, the minimization of the formation of bainite and secondary phases in the steels would be beneficial for preventing or minimizing separations because separations deteriorated low-temperature impact toughness. |
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| Key Words |
| API X80 Linepipe steel, charpy impact test, separation |
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