Duplex stainless steels are characterized by their biphasic, ferritic-austenitic microstructure. The ideal volumetric fraction of these phases in duplex stainless steels, is of 50% ferrite and 50% austenite, however, this condition is difficult to be obtained when arc welding these materials. A detailed analysis of the effect of relative plate thickness in the heat flow and, consequently, in the cooling rate during welding of duplex stainless steel is of fundamental importance. The correct adjustment of the welding parameters leads to an optimum cooling rate of the joint, which guarantees a good balance of the volume fractions of ferrite and austenite, and results in acceptable mechanical properties and corrosion resistance. In this work, the best welding practices to the duplex stainless steel UNS S32750 (Super Duplex) were studied, guaranteeing welded joints that showed the ideal volumetric fractions of ferrite and austenite and, consequently, the mechanical properties according to the project. Complementary techniques of microstructural analysis were used, such as optical emission spectrometry, optical microscopy and quantitative image analysis.