Effect of variable polarity during cold metal transfer on microstructure and mechanical properties of directed energy deposition-arc built 2209 duplex stainless steel

Duplex stainless steel (DSS) is recently considered as a promising candidate to replace traditional bronze-based alloys in medium to large sized ship propellers, due to its combination of advantages including excellent specific strength and corrosion resistance. Directed energy deposition-arc (DED-arc) is chosen as the preferred method to make ship propellers because of its flexibility and high efficiency. However, excessive austenite is formed in the DSS deposits due to severe heat accumulation caused by DED-arc process, which greatly limits the mechanical properties of DSS. Therefore, arc process with lower thermal accumulation effects is crucial for achieving a more ideal phase ratio of DSS deposits. In this study, a variable polarity cold metal transfer (VP-CMT) mode with more lower heat input is applied to the DED-arc process to further reduce the heat accumulation and austenite. Obtained characterization results have confirmed the effectiveness of VP-CMT mode in decreasing austenite volume fraction in both as-deposited and reheated zones, therefore under the same wire feed and travel speeds, VP-CMT produces higher strength DSS components than normal CMT. Also, the lower line energy input of VP-CMT leads to smaller reheated zone in DSS buildup walls, such morphology difference further induces larger tensile property anisotropy than normal CMT sample. VP-CMT shows more potential in controlling the ferrite/austenite ratio to equilibrium than normal CMT.