Avaliação da soldabilidade do aço inoxidável duplex UNS S31803 pelo processo MIG/MAG curto-circuito convencional

Abstract

Duplex stainless steel (DSS) is an alloy that, by allying both good mechanical properties and excellent corrosion resistance, comes increasing industrial interest every day. These attractions make it widely used in the most diverse industrial sectors such as pulp and paper industry, nuclear power, processing, oil and gas, among others. Its wide application in several industrial sectors constantly demands that this material is subjected to some welding process. Its high corrosion and mechanical resistance are attributed to balanced microstructure in approximately 50% ferrite and 50% austenite. In the present work, UNS S31803 AID plates were welded in a 45° bevel by conventional short circuit MIG/MAG process, using five different weld energies, in the range of 0.5-0.7 kJ / mm. The results showed that the effect of the welding energy on the ferrite volumetric fraction was very marked in the heat affected zone (HAZ), and in the weld metal this effect was not so pronounced. It was possible to observe an increase in austenite content with addition of 3% of nitrogen in the shielding gas on weld metal and HAZ, compared to the same energy conditions without this addition. Were no observed intermetallic phases, nitrides or carbides formed in a significant way. Hardness and corrosion resistance (potentiodynamic polarization) were evaluated as a function of welding energy employed. In general, both hardness and intergranular corrosion resistance were not influenced when the welding conditions were compared. The fracture toughness was evaluated by the Crack Tip Opening Displacement technique (CTOD) as a function of welding energy. In general, they did not suffer significant influence when the welding conditions were compared to the base metal. The microstructural changes after the conventional MIG/MAG short circuit welding process, following the presented methodologies, have not modified the corrosion and mechanical resistance of the welded joint significantly.