Experimental study on the mechanical performance and corrosion resistance of welds between API X70 and DSS 2205 for marine applications

Dissimilar welds between 2205 duplex stainless steel and American Petroleum Institute (API) X70 pipeline steel were produced by shielded metal arc welding using electrodes extruded from a laboratory-developed CaO–CaF 2 –TiO 2 –ZrO 2 –SiO 2 coating on ER2209 core wire, and compared with a commercial ER2209 electrode. Twenty-seven coating formulations were screened against weldability, weld-metal chemistry and bead microhardness, and the ten that satisfied every constraint were ranked by a weighted desirability function; the selection proved insensitive both to the weights adopted and to the aggregation rule. The joints show a strength–ductility trade-off rather than a uniform advantage for either consumable. The commercial electrode gave marginally higher tensile strength (682.23 against 674.64 MPa) and a harder weld zone, whereas the developed electrode gave 18.9% greater elongation, higher absorbed impact energy and a flatter hardness profile across the joint. Both joints exceeded the strength of the X70 base metal. Microstructural examination confirmed a ferrite–austenite weld structure containing grain-boundary, Widmanstätten-like and intragranular austenite. Potentiodynamic polarisation in 3.5% NaCl gave weld-zone corrosion currents of the same order for both consumables, the difference lying within the uncertainty of Tafel extrapolation on passive alloys. The X70-side heat-affected zone was the least corrosion-resistant region of both joints.