Improving mechanical performance of resistance spot welded joints of AISI 409M steel by double pulse current

In the present work, the influence of the cooling time on the mechanical performance, hardness, and microstructural features of a double pulse resistance spot welded medium-Mn steel are investigated. Curves of the electrical resistance throughout the welding revealed that the cooling time strongly influences the heat generation during the second pulse. A second pulse after a short cooling time re-melts the center, and heat treats the edge of the primary fusion zone. This desired in-process heat treatment leads to a modification of the cast-like martensitic structure by recrystallization illustrated by electron backscatter diffraction measurements and to a homogenization of manganese segregations, visualized by energy-dispersive X-ray spectroscopy, which results in an enhanced mechanical performance during the cross tension strength test. In contrast, during excessively long cooling times, the resistance drops to a level where the heat generation due to the second pulse is too low to sufficiently re-heat the edge of the primary FZ. As a consequence, the signs of recrystallization disappear, and the manganese segregations are still present at the edge of the fusion zone, which leads to a deterioration of the mechanical properties.

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Resistance spot welding. Destructive tests of welds. Method for the fatigue testing of spot welded joints

10.3403/02852592 ◽

2003 ◽

Cited By ~ 1

Keyword(s):

Welded Joints ◽

Resistance Spot Welding ◽

Spot Welding ◽

Fatigue Testing ◽

Resistance Spot ◽

Spot Welded

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Microstructure and Mechanical Performance of Resistance Spot Welded Martensitic Advanced High Strength Steel

Processes ◽

10.3390/pr9061021 ◽

2021 ◽

Vol 9 (6) ◽

pp. 1021

Author(s):

Yunzhao Li ◽

Huaping Tang ◽

Ruilin Lai

Keyword(s):

Mechanical Properties ◽

Failure Modes ◽

Mechanical Performance ◽

Strong Dependence ◽

High Strength ◽

Weld Nugget ◽

Resistance Spot ◽

Pull Out ◽

Cross Tension ◽

Spot Welded

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.

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