Characterization of microstructural and mechanical properties of Inconel 625/A517 high strength quenched and tempered steel dissimilar welds

Dissimilar welding between Inconel 625 nickel base superalloy and high strength quenched and tempered A517 Gr.B steel investigated by pulsed ND:YAG laser beam welding equipment. This joint has special application at submarine components. After welding, the optimized joint microstructure including the weld metal and heat affected zones were characterized by optical and scanning electron microscopy (SEM). The results showed a fine dendritic structure and existence of large amount of Niobium carbide and Laves eutectic phase in the weld metal. Energy-dispersive X-ray spectroscopy (EDS) analysis showed Nb and Mo segregation to interdendritic zones at the weld metal. Grain growth in the heat affected zone of Inconel 625 did not occur, however, ultrafine precipitations were deposited at the heat affected zone. An approximately 65 µm wide transition zone was observed at the steel and weld zone interface; consisted of a martensitic layer (10-20µm) along the weld interface and the austenite phase region with a little ferrite adjacent to the base metal. The tensile test and micro hardness test of the optimized sample was investigated. The electrochemical behavior of the weld metal was investigated at room temperature in 3.5% NaCl solution using potentiodynamic polarization. The results show that the corrosion resistance of weld metal is more than that of Inconel 625 and less than that of A517 Gr.B. It can be concluded that a proper selection of laser beam welding parameters provides sound, fully-penetrated welds.