Abstract
Friction stir processing is a novel solid-state process to modify microstructures and their properties by intense, localized plastic deformation. However, little research has been reported for microstructure evolutions of advanced high-strength steels during the process. The present work focuses on the study of transient microstructure changes and local mechanical properties for friction stir spot processed dual-phase (DP) 980 MPa grade steel (DP980) under different peak temperatures. A pinless silicon nitride ceramic tool was used to produce relatively simple material deformation and flow near the tool. Friction stir spot processed steel samples were characterized by optical and electron microscopies. Furthermore, Vickers microhardness and nano-indentation measurements were used to study local mechanical properties for correlation with microstructures. A swallow layer of refined grains (<0.6 µm) was obtained with a low peak temperature (under 400◦ C), whereas higher peak temperatures (>Ac1) led to a change in grain size with different microstructures (fine-grained DP or martensite). Electron back-scattered diffraction characterizations revealed a large deformation in the as-received microstructures (mixture of ferrite and tempered martensite) induced by friction stir spot processing, leading to recrystallization and grain refinement around the stirred zone. Also, nano-indentation measurements showed a higher hardness than the hardness of the as-received DP980. Friction stir processing with different process conditions effectively changed microstructures and local mechanical properties.
Original language | English |
---|---|
Article number | 4406 |
Pages (from-to) | 1-20 |
Number of pages | 20 |
Journal | Materials |
Volume | 13 |
Issue number | 19 |
DOIs | |
State | Published - Oct 1 2020 |
Funding
Steel Research Laboratory, JFE Steel Corporation, Chiba 260-0835, Japan; [email protected] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; [email protected] (Y.C.L.); [email protected] (A.F.-B.) Correspondence: [email protected] This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). Funding: This research was funded by JFE Steel Corporation in Japan under contract number NFE-17-06928. Acknowledgments: Oak Ridge National Laboratory (ORNL) is managed by UT-Battelle, LLC, for the US Department of Energy under contract DE-AC05-00OR22725. The authors acknowledge Alan Frederick and Doug Kyle at the Materials Joining Group in ORNL for supporting the experiments.
Keywords
- Advanced high-strength steel
- Characterization
- Friction stir processing
- Microstructures