Mechanical reliability of TWIP steel spot weldings

TWIP steel weld spots were produced by varying the following welding parameters: welding current, welding time and electrode clamping force. Hardness distributions along the weld spots cross section were obtained by Vickers microindentations. The mechanical strength and failure modes of the weld spots were assessed by tensile-shear tests. Weibull statistics was applied to statistically analyse the data from tensile-shear loading. The results highlighted the influence of welding parameters variations on the Vickers hardness and residual stress state. These properties have a positive correlation to the failure modes and so the mechanical reliability of the weld spots. Welds that failed in pullout mode and partial-interfacial failure mode have statistically higher load bearing capacity than those in interfacial failure mode. The combination of a welding current of 8 kA with a welding time of 16 cycles and an electrode clamping force of 2 IN showed to be the optimum parameters for the investigated TWIP steel weld spots. By using this optimum setup, it was possible to supress interfacial failure mode and to obtain pullout as the predominant failure mode, considerably increasing the mechanical reliability of the weld spots.