Effect of Ni interlayer on microstructures and mechanical properties of 2205 duplex stainless steel joint by laser oscillating welding

Laser oscillating welding of 2205 duplex stainless steel was performed using Ni interlayer as filler material. The influence of stirring effect caused by laser oscillating and Ni addition in the behavior of molten pool and the microstructure evolution was investigated. The results shows that Ni addition decreased the ratio of chromium equivalent and nickel equivalent in the molten pool and accelerated the austenitic transformation. The austenite/ferrite ratio was regulated, and the precipitation of nitrides was suppressed in the weld seam. The stirring effect caused by the oscillating beam facilitated the uniform distribution of Ni elements within the molten pool, promoting the formation of the homogeneous microstructures in the weld seam. With increasing the thickness of Ni interlayer, both the dimension and the peak temperature of molten pool decrease, further increasing the cooling rate and refining the grain size. When the thickness of Ni interlayer was 50 mu m, the austenite/ferrite ratio in the weld seam was close to 1:1, and the grain size reached the minimum value. The tensile strength and ductility of the welded joint using Ni interlayer with thickness were 774 MPa and 25%, respectively, significantly improving the mechanical properties of 2205 duplex stainless steel joint welded without Ni addition.