Effects of CNTs addition on the microstructure and microhardness of stainless steel alloy/carbon-manganese non-alloyed steel welding

In recent years some progress has been made about the addition of Carbon Nanotubes (CNTs) in the stainless steel metal matrix by pulsed Gas Tungsten Arc Welding (P-GTAW). Despite that, there is lack of information regarding to microstructural modifications induced by CNTs in dissimilar welding. In this sense, we present the welding of nanocomposite based on Nickel/Carbon Nanotubes-stainless steel 316L alloy (Ni/CNTs-SS 316L), as the welding metal, on carbon-manganese (C-Mn) non-alloyed structural steel, as the base metal. The microstructure of manufactured specimens with/without nanocomposite was characterized by: optical microscopy; Raman spectroscopy; scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and electron backscattering diffraction (EBSD). Moreover, Vickers tests were performed from the welding metal (WM) to the base metal (BM) before/after temper treatment in order to investigate the microhardness changes. The results show that dilution rate and grain size for specimen with nanocomposite was higher than without nanocomposite; the CNTs affected the misorientation angle and texture of the WM; the topside microhardness from WM with Ni-CNTs was on average 30.40% higher than BM; and, in transverse cross-section microhardness was 31% higher than control sample on average at fusion line zone. These results indicate that addition of CNTs in the metallic matrix by dissimilar welding is a fertile ground for new studies applicable to manufacturing industry.