Microstructural, Mechanical, and Electrochemical Analysis of Duplex and Superduplex Stainless Steels Welded with the Autogenous TIG Process Using Different Heat Input

Abstract

Duplex Stainless Steels (DSS) and Superduplex Stainless Steels (SDSS) have a strong appeal in the petrochemical industry. These steels have excellent properties, such as corrosion resistance and good toughness besides good weldability. Welding techniques take into account the loss of alloying elements during the process, so this loss is usually compensated by the addition of a filler metal rich in alloying elements. A possible problem would be during the welding of these materials in adverse conditions in service, where the operator could have difficulties in welding with the filler metal. Therefore, in this work, two DSS and one SDSS were welded, by autogenous Tungsten Inert Gas (TIG), i.e., without addition of a filler metal, by three different heat inputs. After welding, microstructural, mechanical, and electrochemical analysis was performed. The microstructures were characterized for each welding condition, with the aid of optical microscopy (OM). Vickers hardness, Charpy-V, and cyclic polarization tests were also performed. After the electrochemical tests, the samples were analyzed by scanning electron microscopy (SEM). The SDSS welded with high heat input kept the balance of the austenite and ferrite, and toughness above the limit value. The hardness values remain constant in the weld regions and SDSS is the most resistant to corrosion.