2205 (S31803/S32205) is an austenitic-ferritic duplex stainless steel with a yield strength about twice that of 304 and outstanding resistance to chloride stress corrosion and pitting corrosion, widely used in chemical, marine, and flue gas desulfurization applications. Welding key points: 1) Heat input should be controlled at 0.5–2.0 kJ/mm; excessive heat input should be avoided as it leads to an excessively high ferrite ratio and grain coarsening; 2) Interpass temperature should not exceed 150°C, with cooling controlled during multi-layer, multi-pass welding; 3) Matching duplex steel filler metal (e.g., ER2209) should be preferred, and shielding gas is recommended to contain nitrogen, Ar+2–3%N2, to stabilize austenite; 4) Post-weld solution treatment is generally not required, but weld oxidation color must be cleaned and pickling and passivation performed. For acceptance, ferrite content testing of the weld (target approximately 35–65%) and corrosion test reports may be required.