Microstructure characterization of duplex stainless steel multi-pass welded joint

Duplex stainless steel (DSS) welded joint was fabricated by tungsten argon arc welding method. Equilibrium phase transformation processes of base material and weld were calculated by thermodynamic method. Microstructures in different zones of DSS welded joint were characterized by optical microscope, scanning electron microscope, energy dispersive spectroscopy, and transmission electron microscopy. The results showed that the Ni addition in the weld significantly promoted austenite (γ) formation and prevented Cr₂N precipitation. The primary austenite (γ₁) in the weld and the heat affected zone (HAZ) mainly consisted of grain boundary austenite, Widmanstatten austenite, and intragranular austenite. There were obvious composition differences in the different types of austenite. Furthermore, there were two types of secondary austenite (γ₂) in both the weld and the HAZ: intragranular and intergranular γ₂. The γ₂ were easy to precipitate within the ferrite (δ) and in the/γ₁ interface where enriched in Ni and N element while depleted in Cr and Mo element. In the HAZ, the Cr₂N were mainly precipitated within the grain, in the/γ₂ interface, and in the/boundary.