Resistance spot welding of dissimilar austenitic/duplex stainless steels: Microstructural evolution and failure mode analysis

Abstract

The paper addresses the microstructural evolution and failure mode analysis for dissimilar resistance spot welding of austenitic and duplex stainless steels. Microstructural examination by optical and scanning electron microscopes revealed that pre-existing TiC particles in the base metal microstructure of the duplex stainless steel were responsible for changing the nature of solid state phase transformations in heat affected zone and columnar to equiaxed transition grain structure in fusion zone due to heterogeneous nucleation. Moreover, it was found that simultaneous occurrence of constitutional liquation of these TiC particles as well as grain boundary sweeping mechanisms led to grain boundary liquation in the heat affected zone of the investigated duplex stainless steel. Failure analysis after the tensile-shear testing revealed that in the partial thickness-partial pullout failure mode fracture initiates in a similar manner as pullout failure mode; and it was found that the work hardening ability of the parent metals is the key controlling factor for crack initiation site.