Comportamento mecânico e resistência à corrosão de juntas soldadas de aços inoxidáveis lean duplex 2101 (S32101): uma análise comparativa dos processos GTAW e GTAW dupla fusão

Abstract

Recently, duplex stainless steels are used in many applications involving corrosive atmospheres in combination with the need for high mechanical strength. These steels have a microstructure with a volumetric fraction of ferrite / austenite in the ratio of 1:1, which provides good mechanical properties compared to traditional ferritic or austenitic stainless steels. However, in welding processes, exposure to high temperatures alters the balance of these two phases and simultaneously promotes the supply of harmful phases. In this work, lean duplex stainless steels of class S32101 were used welded using the GTAW and GTAW-DF (double fusion) processes. The studied material is a representative of the “lean duplex” category, where Ni and Mo from conventional duplex steel (S32205) are partially replaced by Mn and N. The objective of this work was to evaluate the effect of process variation on the properties of the welded joint since the difference between the GTAW process and the GTAW-DF is due to the fact that there is a second heat input due to the second torch welding synchronously on the opposite side in the GTAW-DF process, which can increase the formation of harmful phases. The evolution of the microstructure in the heat-affected zone (HAZ) and the weld was evaluated by optical microscopy and the mechanical performance was evaluated through tensile, hardness, impact and bending tests, in addition to pitting corrosion tests. With the results of this study, it was possible to verify the increase in austenite and nitrides in the HAZ of the GTAW-DF process, without significant losses in the corrosion test and mechanical tests. Conventional GTAW was shown to be less reliable than GTAW-DF as it showed porosity in the radiography test and cracks in the bending test. Despite the thermal effects of GTAW-DF, it was evaluated more reliably and the effects were compressive for welding joints in this material.