TY - JOUR
T1 - Effects of finish rolling temperature on inverse fracture occurring during drop weight tear test of API X80 pipeline steels
AU - Sung, Hyo Kyung
AU - Sohn, Seok Su
AU - Shin, Sang Yong
AU - Lee, Sunghak
AU - Kim, Nack J.
AU - Chon, Seung Hwan
AU - Yoo, Jang Yong
PY - 2012/4/15
Y1 - 2012/4/15
N2 - In this study, drop-weight tear tests (DWTT) were conducted on API X80 pipeline steels fabricated with different finish rolling temperatures in order to analyze abnormal fracture appearance, i.e., inverse fracture, occurring in the region impacted by a hammer. Area fractions of fracture modes were measured from fractured DWTT specimens, and the measured data were analyzed in relation to microstructures, DWTT absorbed energy, and strain hardening of the hammer-impacted region. As the finish rolling temperature decreased, the volume fraction of fine-grained acicular ferrite increased, while that of large-grained upper bainite or granular bainite decreased. According to the DWTT results, the absorbed energy tended to increase with increasing volume fraction of acicular ferrite (with decreasing finish rolling temperature). A large area of inverse fracture of cleavage type was found in the hammer-impacted region of the steels fabricated with high finish rolling temperatures, but the area fraction of inverse fracture was reduced in the steels fabricated with low finish rolling temperatures. Since the area fraction of inverse fracture was closely related with strain hardening of the hammer-impacted region, it could be successfully reduced by lowering strain hardening and by promoting the formation of acicular ferrite via low finish rolling temperatures.
AB - In this study, drop-weight tear tests (DWTT) were conducted on API X80 pipeline steels fabricated with different finish rolling temperatures in order to analyze abnormal fracture appearance, i.e., inverse fracture, occurring in the region impacted by a hammer. Area fractions of fracture modes were measured from fractured DWTT specimens, and the measured data were analyzed in relation to microstructures, DWTT absorbed energy, and strain hardening of the hammer-impacted region. As the finish rolling temperature decreased, the volume fraction of fine-grained acicular ferrite increased, while that of large-grained upper bainite or granular bainite decreased. According to the DWTT results, the absorbed energy tended to increase with increasing volume fraction of acicular ferrite (with decreasing finish rolling temperature). A large area of inverse fracture of cleavage type was found in the hammer-impacted region of the steels fabricated with high finish rolling temperatures, but the area fraction of inverse fracture was reduced in the steels fabricated with low finish rolling temperatures. Since the area fraction of inverse fracture was closely related with strain hardening of the hammer-impacted region, it could be successfully reduced by lowering strain hardening and by promoting the formation of acicular ferrite via low finish rolling temperatures.
KW - API X80 pipeline steels
KW - Acicular ferrite
KW - Drop-weight tear tests
KW - Finish rolling temperature
KW - Inverse fracture
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U2 - 10.1016/j.msea.2012.02.019
DO - 10.1016/j.msea.2012.02.019
M3 - Article
AN - SCOPUS:84862783760
SN - 0921-5093
VL - 541
SP - 181
EP - 189
JO - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
JF - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
ER -