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Article

Analysis of Fracture Modes of Resistance Spot Welded Hot-Stamped Boron Steel

1
Shanghai Key Laboratory of Digital Manufacture for Thin-Walled Structures, Shanghai Jiao Tong University, Shanghai 200240, China
2
State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, Shanghai 200240, China
*
Author to whom correspondence should be addressed.
Metals 2018, 8(10), 764; https://doi.org/10.3390/met8100764
Received: 4 September 2018 / Revised: 23 September 2018 / Accepted: 25 September 2018 / Published: 26 September 2018
Fracture modes of resistance spot welded ultra-high strength hot-stamped boron steel via lap-shear test are different from that of the traditional advanced high strength steel due to the difference in geometrical size and material property of the spot welds. In this paper, lap-shear fracture modes of resistance spot welding joints were analyzed and joint characteristics that affecting the fracture behavior were discussed. Three fracture modes were found to change from interfacial fracture (IF) to pull-out fracture (PF) with the increase of nugget diameter. For PF I mode, the fracture initiated at the transition zone between the fusion zone and upper-critical heat affected zone (HAZ) and propagated along the thickness of the nugget. For PF II mode, during which the failure initiated at the sub-critical HAZ where the softest zone occurred, and it propagated to the base material. Obvious hardness decrease was observed in the transition zone with the formation of the delta ferrite at the fusion boundary due to the relatively high amount of alloying element in the hot-stamped boron steel, which could provide the reason for route of PF I extending along this zone. Fluctuation in the hardness in the transition zone led to the existence of both PF I and PF II at the same welding current. View Full-Text
Keywords: hot-stamped boron steels; fracture modes; lap shear test; resistance spot welds; transition zone hot-stamped boron steels; fracture modes; lap shear test; resistance spot welds; transition zone
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MDPI and ACS Style

Zhao, Y.; Zhang, Y.; Lai, X. Analysis of Fracture Modes of Resistance Spot Welded Hot-Stamped Boron Steel. Metals 2018, 8, 764. https://doi.org/10.3390/met8100764

AMA Style

Zhao Y, Zhang Y, Lai X. Analysis of Fracture Modes of Resistance Spot Welded Hot-Stamped Boron Steel. Metals. 2018; 8(10):764. https://doi.org/10.3390/met8100764

Chicago/Turabian Style

Zhao, Yixi, Yansong Zhang, and Xinmin Lai. 2018. "Analysis of Fracture Modes of Resistance Spot Welded Hot-Stamped Boron Steel" Metals 8, no. 10: 764. https://doi.org/10.3390/met8100764

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