Microstructure Evolution and Selective Corrosion Resistance in Underwater Multi-pass 2101 Duplex Stainless Steel Welding Joints

A recently developed promising material, 2101 lean duplex stainless steel, represents an alternative to 304 austenite stainless steel. In this work, multi-pass 2101 weld joints were fabricated using the flux-cored arc welding method in a hyperbaric chamber. The pressure varied from 0 to 0.75 MPa. The evolution of the welding process and microstructure was investigated. γ₂ formation in the reheated zones of the WM and HAZ was not uniform. The closer the reheated zone is to the subsequent heat source, the greater the γ₂ formation in the reheated zone. Sufficient primary austenite transformation inhibited Cr₂N precipitation and the subsequent intragranular γ₂ formation in the reheated weld passes of the 0.45 MPa weld metal. The localized corrosion resistance of each zone of the 0.45 MPa DSS joint was measured using non-destructive double-loop electrochemical potentiokinetic reactivation tests. The localized corrosion was induced by γ₂ and Cr₂N. The root region of the 0.45 MPa weld metal underwent two subsequent welding thermal cycles, which induced increased γ₂ formation and lower resistance to corrosion because of the decreased pitting resistance value of γ₂. The correlation between microstructure evolution and the distribution of selective corrosion was determined.