Processing, microstructure, mechanical properties and corrosion susceptibility of ferritic/austenitic dissimilar welds produced by FSW

Abstract

This study aimed to investigate the dissimilar welding of ferritic and austenitic stainless steels, through different joint configurations AISI 410S / 304L and AISI 444 / 316L, by the friction stir welding process (FSW), evaluating operational and metallurgical aspects. The FSW welding of different joints in this study was performed at the Helmholtz-Zentrum Geesthacht (Germany) due to establishing a cooperation agreement with the Universidade Federal do Ceará. The welding parameters range on setting was based on the best parameters found on the FSW similar welding for these steels. Changes in the parameters were performed to determine an acceptable combination of surface finish, absence of cracks and good penetration. The better welding conditions for each welded joint configuration were subjected to mechanical evaluation through the tensile, bending, and microhardness tests. In the same way, for samples from the better welding conditions were extracted for corrosion resistance evaluation through DL-EPR, Salt Spray and Immersion Oil tests. In these conditions, microstructural analysis was performed by optical microscopy (OM) and scanning electron microscopy (SEM). The electron backscatter diffraction (EBSD) with inverse pole figure (IPF) map and Kernel Average Misorientation (KAM) was also used in some conditions to help understand recrystallised fraction and grain orientation. The results from microscopy techniques allow the correlation between process parameters and microstructure with the mechanical properties and corrosion resistance. For the AISI 410S/304L dissimilar welds, it was possible to observe a grain size refinement and increase in microhardness values in HAZ, TMAZ and SZ, with better results in the tensile test concerning the base metal of the AISI 410S steel and low sensitisation levels and corrosion rates in the salt spray test. AISI 444 / 316L dissimilar welded joints were produced with excellent grain refinement, absence of defects and undesirable phases, high cohesion between the two materials and good results in the yield and tensile strength, without loss of the intergranular corrosion resistance of the joints. Therefore, based on the corrosion resistance and mechanical testing, it is possible to conclude that AISI 410S/304L and AISI 444/316L stainless steel dissimilar welds can be successfully performed by the FSW process with enhanced microstructural features.