Abstract
Resistance spot welded 1.2 mm (t)-thick 1400 MPa martensitic steel (MS1400) samples are fabricated and their microstructure, mechanical properties are investigated thoroughly. The mechanical performance and failure modes exhibit a strong dependence on weld-nugget size. The pull-out failure mode for MS1400 steel resistance spot welds does not follow the conventional weld-nugget size recommendation criteria of 4t0.5. Significant softening was observed due to dual phase microstructure of ferrite and martensite in the inter-critical heat affected zone (HAZ) and tempered martensite (TM) structure in sub-critical HAZ. However, the upper-critical HAZ exhibits obvious higher hardness than the nugget zone (NZ). In addition, the mechanical properties show that the cross-tension strength (CTS) is about one quarter of the tension-shear strength (TSS) of MS1400 weld joints, whilst the absorbed energy of cross-tension and tension-shear are almost identical.
Highlights
With the development of science and technology and improvements in the standard of living, the safety, energy saving and environmental protection of automobiles has increasingly become the research focus of interest
cross-tension strength (CTS) decline rapidly due to the occurring expulsion
320ms varied to determine their roles in the mechanical properties of welded MS1400
Summary
With the development of science and technology and improvements in the standard of living, the safety, energy saving and environmental protection of automobiles has increasingly become the research focus of interest. Advanced high strength steels (AHSS), due to their excellent strength and formability, have accelerated the integration of AHSS into the automotive architecture to reduce weight, improve fuel efficiency and increase the crashworthiness of vehicles through enhanced mechanical properties [1,2,3,4,5]. Sound quality assurance and high efficiency, resistance spot welding (RSW) is the most predominant welding technique adopted for joining AHSS in automotive applications [12,13,14]. There are three critical factors for the quality evaluation of resistance spot welds, including weld-nugget size, weld mechanical performance and failure mode. Weld-nugget size is the most important parameter determining weld mechanical performance and failure mode
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