期刊
JOURNAL OF MATERIALS PROCESSING TECHNOLOGY
卷 306, 期 -, 页码 -出版社
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jmatprotec.2022.117621
关键词
Friction stir welding; Medium-Mn steel; Intercritical annealing; Reversed austenite
资金
- National Nature Science Foundation of China [51774085]
- Liaoning Province Excellent Youth Foundation [2020-YQ-03]
- Open Research Fund from the State Key Laboratory of Rolling and Automation, Northeastern University [2020RALKFKT009]
This study successfully improved the toughness and ductility of medium-Mn steel joints through friction stir welding and intercritical annealing. The as-annealed joints exhibited higher impact energy and elongation, which can be attributed to the high proportion of high angle boundaries and a large amount of ultra-fine reversed austenite.
The medium-Mn steels have a great application potential in the engineering fields due to its excellent strength and toughness. However, the presence of coarse martensite and segregation of Mn in the fusion-welded mediumMn steel joint severely deteriorated toughness and ductility. In this work, 6 mm thick medium-Mn steel plates were joined by friction stir welding, and then were intercritically annealed to enhance the toughness and ductility of the joint. The as-welded nugget zone (NZ) contained lath martensite with low proportion of high angle boundaries (HABs), leading to the joint with lower elongation of 22.5% and the impact energy of 73.6 J/cm(2). However, the as-annealed NZ consisted of ferrite and austenite because partial martensite changed to reversed austenite, while other martensite became ferrite during annealing. In addition, the proportion of HABs in the as-annealed NZ increased obviously. In comparison with as-welded joint, the impact energy and elongation of the as-annealed joint was increased by 70.7% and 44.4%, respectively. The abovementioned excellent mechanical properties were attributed to the high proportion of HABs and a large amount of ultra-fine reversed austenite with high thermal and mechanical stability, which provided a significant transformation induced plasticity effect, obviously inhibiting crack initiation and propagation. This systematic work provided a reference for welding similar materials containing retained austenite.
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