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Vol.42, No.3, 238 ~ 249, 2004
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| Title |
| Fracture Properties of High-Toughness API X70 Pipeline Steels 2. Effect of Alloying Elements on Toughness and Transition Temperature |
| 황병철 Hwang Byeong Cheol , 이성학 Lee Seong Hag , 김영민 Kim Yeong Min , 김낙준 Kim Nag Jun , 안성수 An Seong Su |
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| Abstract |
| This study is concerned with the effects of microstructure on fracture properties of high-toughness API X70 pipeline steels. Three kinds of steels were fabricated by varying alloying elements such as C, Cu, and Mo, and their microstructures were varied by the rolling conditions such as finish rolling temperature and finish cooling temperature. Charpy V-notch (CVN) impact test and press notch (PN) drop-weight tear test (DWTT) were conducted on the rolled steel specimens in order to analyze low-temperature fracture properties. Charpy impact test results indicated that the specimens rolled at the γ single phase region of the steel having the reduced C and Mo content had high upper shelf energy (USE) and low energy transition temperature (ETT) because of the appropriate formation of quasi-polygonal or polygonal ferrite and the decreased fraction of martensite-austenite constituent. Most of the specimens rolled at γ region also showed excellent DWTT properties as the percent shear area well exceeded 85%, irrespective of finish cooling temperatures, while their USE was higher than that of the specimens rolled at the (α+γ) two phase region. Thus, overall fracture properties of the specimens rolled at rolled at γ region were better than those of the specimens rolled at (α+γ) region, considering both USE and DWTT percent shear area. |
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| Key Words |
| API X70 pipeline steel, Alloying element, Rolling condition, Charpy V-notch, CVN, impact test, Drop-weight tear test |
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