Analysis of Fracture Modes of Resistance Spot Welded Hot-Stamped Boron Steel
Abstract
:1. Introduction
2. Experimental Procedure
2.1. Materials
2.2. Sample Fabrication
2.3. Cross-Sectional Examinations
2.4. Tensile-Shear Test
3. Results and Discussion
3.1. Typical Fracture Mode
3.2. Fracture Route
4. Discussion
4.1. Microhardness Distribution
4.2. Microstructure
5. Conclusions
- (1)
- Three fracture modes (IF, PF I and PF II) were found in lap-shear test of resistance spot welded B1500 joint. With the increase of nugget diameter, the fracture mode tended to change from IF to PF. Fracture route of IF extended along the interface of the nugget, while route of PF extended along the transition zone between nugget and upper critical zone. The PF II mode had the maximum lap shear force and fracture energy.
- (2)
- At the welding current of 5.6 KA, IF mode initiated at the sheet interface and propagated towards the FZ and failed through the sheet. At higher welding currents and thus larger nugget size, a fracture mode will transit from IF to PF mode. For PF I mode, the fracture initiated at the FZ/UC zone and propagated along the thickness of the nugget, thus the nugget was pulled out from one sheet. For PF II mode, during which the failure initiated at the SCHAZ where the softest zone occurred and propagated to the BM side, indicating more reliability of the welds.
- (3)
- Obvious hardness decrease was observed in the transition zone of B1500 joint, which could provide the reason for route of PF I extending along this zone. This phenomenon can be explained 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. Fluctuation of the hardness in the transition zone led to the existence of both PF I and PF II at the same welding current.
Author Contributions
Funding
Conflicts of Interest
References
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Steel | Chemical Composition in wt. % | ||||||
---|---|---|---|---|---|---|---|
C | Si | Mn | Cr | Ti | Al | B | |
B1500 | 0.23 | 0.24 | 1.19 | 0.18 | 0.04 | 0.03 | 0.0023 |
Steel | Mechanical Properties | ||
---|---|---|---|
Yield Strength (MPa) | Tensile Strength (MPa) | Elongation (%) | |
B1500 | 1250 | 1530 | 7 |
Parameters | Electrode Force (kN) | Welding Current (KA) | Squeeze Time (ms) | Weld Time (ms) | Hold Time (ms) |
---|---|---|---|---|---|
Value | 6.0 | 5.2~8.0 | 1000 | 580 | 200 |
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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
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 StyleZhao, 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
APA StyleZhao, Y., Zhang, Y., & Lai, X. (2018). Analysis of Fracture Modes of Resistance Spot Welded Hot-Stamped Boron Steel. Metals, 8(10), 764. https://doi.org/10.3390/met8100764