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Metals 2019, 9(3), 285; https://doi.org/10.3390/met9030285

Microstructure and Properties of Spot Welded Joints of Hot-Stamped Ultra-High Strength Steel Used for Automotive Body Structures

1
Tianjin Key Laboratory of Refrigeration Technology, Tianjin University of Commerce, Tianjin 300134, China
2
School of Mechanical, Materials, Mechatronics and Biomedical Engineering, University of Wollongong, Northfields Avenue, Wollongong, NSW 2500, Australia
3
School of Mechanical Engineering, Tianjin University of Commerce, Tianjin 300134, China
*
Author to whom correspondence should be addressed.
Received: 1 February 2019 / Revised: 24 February 2019 / Accepted: 26 February 2019 / Published: 2 March 2019
(This article belongs to the Special Issue Characterization of Welded Joints)
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Abstract

Hot-stamped ultra-high strength steels have been widely used in automobile structural parts. Considering the high splash tendency in resistance spot welding due to their extremely high hardness, in this work, microstructural characteristics and mechanical performance of the resistance spot welded ultra-high strength steels are investigated. The results indicate that the interface between the nugget and heat-affected zone (HAZ) is the weakest zone where fractures initiate. In tensile shearing tests, a qualified spot welding joint failed with a button-shaped fracture. Welding defects would significantly decrease the load-carrying capacity and lead to interfacial fracture, except for a button-shaped fracture. In spot welding, it was found that a specific mid-frequency alternating current (AC) input mode, in which a 6 ms cooling cycle was inserted between every two neighboring current pulses, can avoid the splash in the spot welding of hot-stamped hardened steels. View Full-Text
Keywords: spot welding; hot-stamped hardened steel; microstructure; martensite; bainite spot welding; hot-stamped hardened steel; microstructure; martensite; bainite
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Qiao, Z.; Li, H.; Li, L.; Ran, X.; Feng, L. Microstructure and Properties of Spot Welded Joints of Hot-Stamped Ultra-High Strength Steel Used for Automotive Body Structures. Metals 2019, 9, 285.

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