Microstructure and mechanical properties of underwater hyperbaric FCA-welded duplex stainless steel joints

The microstructure and mechanical properties of underwater hyperbaric flux-cored arc (FCA) welded duplex stainless steel joints were investigated. Ferrite in the heat-affected zone (HAZ) and weld metal (WM) exhibited the same primary micro-texture as the base metal (BM). Austenite in the different zones exhibited different micro-textural components. The low-energy Sigma 3 austenite grain boundaries in the BM were almost two times greater in number than those in the HAZ and WM. Abundant ferrite along with Cr2N precipitation in the HAZ increased the dislocation density and microhardness of the HAZ, but was detrimental to the elongation of the joint. A balanced ferrite-austenite microstructure in the WM inhibited Cr2N precipitation. The strength and microhardness of the WM were the highest, with a good elongation of more than 30%. The absorbed energies of the BM and WM at -40 degrees C met the ASTM A923 requirements. This welding process can be used for the maintenance of the spent fuel storage pools.