Influence of Novel Torch Type on Mechanical and Microstructural Characteristics of Cold Metal Transfer Brazed Joints

The present study aimed to braze interstitial free (IF) steel by using novel Braze+ and conventional Robacta torches with the aid of CuAl8 filler wire for a range of heat input 72-250 J/mm. Results showed that focused/denser arc and smaller arc action range, i.e., lower heat loss in the case of Braze+ torch resulted in better wettability, thicker intermetallic layer at the interface of deposited bead-steel, and higher dispersive phase fraction in the bead compared to Robacta torch which ultimately contributed to the evolution of mechanical properties of brazed joints. Furthermore, wettability, thickness of intermetallic layer and fraction of dispersive phases increased with the heat input due to increased deposition rate per unit time, availability of reacting atoms near the interface, and melting of base metal, respectively. Hardness variation of the brazed joints revealed that base metal was prone to failure due to comparatively higher hardness as well as improved resistance to failure of HAZ (due to the formation of acicular ferrite) and deposited bead (due to dispersion hardening). In addition, Fe, Al, and Cu were the main constituents of intermetallic layer and dispersive phases in the bead. IMC layer was harder in the case of Braze+ torch due to comparatively higher Fe content. Two modes of failure namely interface (brittle features) and base metal (ductile features) were observed during shear-tensile testing.