The effect of N₂ addition upon the MIG welding process of duplex steels

This paper presents the results of a study on the weldability of a duplex stainless steel, Avesta 2205, carried out by GMAW (MIG) pulsed arc welding process. An AISI 2209 electrode (AWS A/SFA 5.9, ER2209) was used as filler metal. The study was focused on the N₂ content in the shield gas, from 0% to 6.4%. Firstly, a microstructural characterization of the welds using scanning electron microscopy (MEB-EDX) was carried out. Also, in order to study the microstructural changes originated by the welding thermal cycles and the % content of the N₂, the ferrite content in the weld pool and heat affected zone (HAZ) were determined. Vickers hardness, tensile and bending tests were performed to determine the mechanical properties of joints and hence the influence of N₂ addition without decrease in the mechanical properties. Finally, the joints were examined for susceptibility to intergranular corrosion using the Standard ASTM 262 93, practice A. The optimal content of N₂ in the shield gas is included between 3% and 5%, which attain to obtain a 94% base material UTS.