A comparison of cross-tension properties and fracture behavior between similar and dissimilar resistance spot-weldments in medium-Mn TRIP steel

Abstract

The current study characterizes the degradation of cross-tension properties in medium-Mn transformation-induced plasticity (TRIP) steel weldments by comparison of fracture behaviors in both similar and dissimilar weldments with DP980 dual phase steel. The experimental results reveal that the cross-tension strengths of medium-Mn TRIP steel weldments is inferior to those of conventional TRIP steel having lower carbon equivalent. Although the failure modes of similar and dissimilar weldments were different from each other, the brittleness of the martensite was a common key factor governing crack propagation. In similar weldment, the decreased tensile toughness in the coarse grain heat-affected zone due to the insufficient self-tempering of martensite and the decreased retained austenite fraction. Meanwhile, understanding the changes in the carbon equivalent caused by dilution in the dissimilar welds and segregation in the fusion zone is necessary to characterize medium-Mn TRIP steel spot welds.