Abstract
The balanced ferrite:austenite (α/γ) ratio is essential for duplex stainless steels (DSSs) to achieve superior strength and corrosion resistance. Nevertheless, the chemical compositions of commercial welding wires are not especially designed for the wire arc additive manufacturing (WAAM) process, leading to excessive austenite formation (∼74%) in their as-built DSSs. In this research, the chemical composition of a flux-cored wire arc additively manufactured super duplex stainless steel (FCWA-AM SDSS) was especially designed based on its thermal-history to achieve the balanced α/γ ratio. Mechanisms describing the microstructure evolution of α and γ during the FCWA-AM process were also proposed. Cr2N was the secondary phase formed in the as-built SDSS, which acted as the nucleating sites of intragranular austenite during the cooling of the deposition layer and precipitated at Widmanstätten austenite boundaries in the subsequent intrinsic heat treatment (IHT). The corrosion tests suggested that a thicker and more stable passive film was formed on the surface of the as-built SDSS than the hot-rolled 2205 DSS but their pitting corrosion resistance were comparable because the precipitation of Cr2N hindered the improvement of pitting corrosion resistance. The as-built SDSS showed higher strength than previously reported WAAM DSSs because of the enhanced solid solution strengthening effect and the balanced α/γ ratio.
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