An investigation on microstructure and properties of dissimilar welded Inconel 625 and SUS 304 using high-power CO2 laser

Microstructure and properties of laser deep penetration welded Inconel 625 nickel-based alloys and SUS304 stainless steel were investigated. Weld microstructures, room temperature tensile properties and stress rupture properties, impact toughness, and hardness of dissimilar welded joints were evaluated. The experimental results showed that the microstructure of fusion zone near the fusion line in the SUS304 side was mainly cellular, whereas that near the fusion line in the Inconel 625 was predominantly columnar dendrites. Laves phases were precipitated at the grain boundary of cellular and in the interdendritic regions of fusion zone in the different form. The white transition layer was generated, and the signification change of concentrations was occurred at the fusion boundary between weld metal and SUS304. The microstructure at the fusion boundary between weld metal and Inconel 625 was characterized by dendritic boundary melting and thickening and accompanied with a lot of Laves phases precipitated in the interdendritic regions. The tensile strength tests indicated that the dissimilar butt joints ruptured in the fusion zone. The toughness of dissimilar weld metal was declined sharply compared to the two base metals. Fractographic analysis revealed that segregation of Nb and Mo in the interdendritic regions deteriorated the tensile strength and toughness of laser dissimilar weld metal. The corrosion resistance of weld metal was higher than that of SUS304 as a considerable amount of Mo elements in the weld metal inhibiting the generation and development of pitting corrosion.