Application fields for duplex stainless steels are drastically increasing. Industries producing and operating petrochemical process equipment, pipelines, bridges, pressure vessels, heat exchangers, rotors, and sea-water systems have a high demand for these steels. In this study, UNS S32205 duplex stainless steel plates of 3 x 40 x 145 mm were TIG welded with welding wires of W22 9 3 NL (2209). The main aim was to investigate the effects of various amounts of magnetic delta-ferrite and other important phases or intermetallic compounds that are formed during and after welding. The phase quantities differing by the welding conditions and argon shielding gas mixtures containing 0, 1, 3, 6, and 9 vol.-% N-2 are studied. The investigations included Charpy V-notch impact tests, weight loss corrosion tests, and microstructural analyses according to ASTM A 923 and magnetic delta-ferrite measurements according to EN ISO 17655, and EN ISO 8249 as well as image analyses according to ASTM E-562, ASTM E 1245 for a comparision of the effect of the amounts of all phases. The differences with respect to the welding parameters were also identified.