CORRELATION BETWEEN MACRO/MICRO STRUCTURE AND MECHANICAL PROPERTIES OF DISSIMILAR RESISTANCE SPOT WELDS OF AISI 304 AUSTENITIC STAINLESS STEEL AND AISI 1008 LOW CARBON STEEL

Structure-properties relationships in dissimilar resistance spot welding of AISI 304 austenitic stainless steel (SS) and AISI 1008 low carbon steel (CS) are investigated. Differences in physical and mechanical properties of both steel sheets affect resistance spot weldability of this combination. Weld nugget shape is asymmetrical and the final fusion line shifts from sheet/sheet interface into the higher resistivity side (i.e. AISI 304). Fusion zone microstructure was ranged from Ferrite-Austenite-Martensite to full martensite depending on the melting/dilution ratio of base metals. Criteria for selection optimum welding condition for dissimilar combination are discussed. It was shown that generally there is a direct relation between mechanical performance (peak load and failure energy) and FZ size of low carbon steel side. The peak load of CS/CS and SS/LCS was nearly same due to the fact that the pullout failure mode of SS/CS welds is initiated from CS base metal. However, the failure energy of the later was greater than the former weld which is a function of higher ductility of SS that helps increasing plastic deformation during process of pullout failure.