Transient Microstructure Evolutions and Local Properties of Dual-Phase 980 MPa Grade Steel Via Friction Stir Spot Processing †
1
Steel Research Laboratory, JFE Steel Corporation, Chiba 260-0835, Japan
2
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
*
Author to whom correspondence should be addressed.
†
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 ).
Materials 2020, 13(19), 4406; https://doi.org/10.3390/ma13194406
Received: 1 September 2020
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Revised: 25 September 2020
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Accepted: 29 September 2020
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Published: 2 October 2020
(This article belongs to the Special Issue Structure and Mechanical Properties of Alloys)
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.
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MDPI and ACS Style
Taniguchi, K.; Lim, Y.C.; Flores-Betancourt, A.; Feng, Z. Transient Microstructure Evolutions and Local Properties of Dual-Phase 980 MPa Grade Steel Via Friction Stir Spot Processing. Materials 2020, 13, 4406. https://doi.org/10.3390/ma13194406
AMA Style
Taniguchi K, Lim YC, Flores-Betancourt A, Feng Z. Transient Microstructure Evolutions and Local Properties of Dual-Phase 980 MPa Grade Steel Via Friction Stir Spot Processing. Materials. 2020; 13(19):4406. https://doi.org/10.3390/ma13194406
Chicago/Turabian StyleTaniguchi, Koichi, Yong C. Lim, Alexis Flores-Betancourt, and Zhili Feng. 2020. "Transient Microstructure Evolutions and Local Properties of Dual-Phase 980 MPa Grade Steel Via Friction Stir Spot Processing" Materials 13, no. 19: 4406. https://doi.org/10.3390/ma13194406
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