Effects of the heat input on the phase balance of the duplex UNS S32205 joined by GTAW

Abstract

The use of duplex stainless steels in industry is increasing due to their characteristics that combine good mechanical and corrosion resistance properties. These steels are comprised of a biphasic structure (50% ferrite and 50% austenite). Therefore, the development of techniques to improve the welding of duplex steels it is necessary, in order to ensure that the phase balance and the material properties are not severely harmed in the process. This paper aims to characterize welded joints with the GTAW process in UNS S32205 duplex stainless steel. Autogenous welds were performed with heat input ranging from 261.00 J/mm and 652.50 J/mm. The next step was the analysis of base metal and weld beads by Vickers hardness testing, EDS, electronic and optical microscopy. The results showed the weld metal region with volume fraction of austenite ranging between 22% and 34%. This variation is due to the lower cooling rates of high heat input values, which allow a greater formation of austenite. About the geometry, it was observed that higher values of heat input, led to wider and deeper welded joints, ranging between 3.9 and 5.9mm width and 0.65 and 1.29mm depth. In the nearest heat affected zone of the weld metal, Vickers hardness showed higher values than the base metal due to the presence of higher percentage of ferrite.