Improvement of circumferential ductility by reducing discontinuities in a high-Mn TWIP steel weldment

Journal Article · Tue May 15 04:00:00 EDT 2018 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2018.03.009· OSTI ID:22804982

Park, Gitae; Jeong, Seonghoon ^[1]; Kang, Heewoong ^[2]; Lee, Changhee ^[1]

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1. Division of Materials Science and Engineering, Hanyang University, 222, Wangsimni-ro, Seongdong-gu, Seoul 04763 (Korea, Republic of)
2. RD Team, Husteel, 131 Bugokgongdan-ro, Songak-eup, Dangjin-si, Chungnam 31721 (Korea, Republic of)

Highlights: • This study focused on two key ways to improve expandability of TWIP steel pipe. • The amount of penetrator is remarkably reduced at low PO{sub 2} welding atmosphere. • The effect of PWHT on the morphological change in the bond line was characterized. - Abstract: Recently, high-frequency electrical resistance welded (HF-ERW) pipes have been introduced as an application of high-Mn twinning induced plasticity (TWIP) steels. However, the excellent ductility of the TWIP steels has been underutilized in expandable pipe applications due to discontinuities in the weldment. This work presents two key ways to improve the pipe expandability or circumferential ductility. In-depth microstructural analysis and flaring tests were conducted to identify bond line discontinuities and to evaluate the circumferential ductility. These results indicate that ductility formed to be strongly related to the welding atmosphere and post-weld heat treatment (PWHT) conditions. The welding atmosphere was related to oxide defects, while the PWHT conditions were related to intrinsic discontinuities. The distribution and amount of penetrator defects along the bond line are the main factors related to the deterioration of the circumferential ductility, which is affected by the sheet metal compositions and decreased remarkably at low PO{sub 2} content. We also suggest that PWHT is necessary for improving the ductility by inducing changes in the bond line texture and hardness distribution. The results were verified based on changes in the crack path propagation.

• OSTI ID: 22804982
• Journal Information: Materials Characterization, Journal Name: Materials Characterization Vol. 139; ISSN 1044-5803; ISSN MACHEX
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CRACKS
DISTRIBUTION
DUCTILITY
ELECTRIC CONDUCTIVITY
HARDNESS
HEAT TREATMENTS
MICROSTRUCTURE
OXIDES
PIPES
STEELS
WELDED JOINTS
WELDING