Microstructure/property relationships in dissimilar welds between duplex stainless steels and carbon steels

The metallurgical characteristics, toughness and corrosion resistance of di ssimilar welds between duplex stainless steel Alloy 2205 and carbon steel A 36 have been evaluated. Both duplex stainless steel ER2209 and Ni-based All oy 625 filler metals were used to join this combination using a multipass, gas tungsten are welding (GTAW) process. Defect-free welds were made with e ach filler metal. The toughness of both the 625 and 2209 deposits were acce ptable, regardless of heat input. A narrow martensitic region with high har dness was observed along the A36/2209 fusion boundary. A similar region was not observed in welds made with the 625 filler metal. The corrosion resist ance of the welds made with 2209 filler metal improved with increasing heat input, probably due to higher levels of austenite and reduced chromium nit ride precipitation. Welds made with 625 exhibited severe attack in the root pass, while the bulk of the weld was resistant. This investigation has sho wn that both filler metals can be used to join carbon steel to duplex stain less steels, but th at special precautions may be necessary in corrosive en vironments.