Shielding gas influence on the ferritic stainless steel weldability

Abstract

Ferritic stainless steels are not characterized by good weldability. Wires made of austenitic stainless steels are usually applied to join ferritic materials because of the good mechanical resistance, tenacity, and ductility reached by austenitic weld metal. However, novel ferritic stainless steel wires, stabilized with niobium and titanium, have been developed to tackle the target of matching the required mechanical properties and keeping the costs lower by using ferritic stainless steels. The characterization of these wires concerning weldability aspects (operational and metallurgical) has not been accomplished yet. The aim of the present study was to investigate the influence of the shielding gas composition (pure argon and mixtures with O2 or CO2) on the chemical composition and microstructure of weld deposits obtained with gas metal arc welding using stabilized ferritic wires (ER430Ti and ER430LNb). The study was made comparatively to a non-stabilized wire (ER430). For each combination gas/wire, three layers of beads were deposited. To prevent interference from base metal dilution, a UNS 43932 was used as support for the layers and only the last layer was analysed. A special experimental approach was applied to permit more reliable comparison among different combinations of wire-shielding gas. Predicted equations for the demanded level of stabilizers in the wire were successfully applied. The results showed that the shielding gas composition played an important role in determining the final chemical composition and microstructure of the deposits, but its effect was dependent on the chemical composition of the deposit as a rule. In general, it was confirmed that the increase in CO2 in the shielding gas augmented the carbon content (and martensite formation) in the weld metal, but wire stabilized with niobium could prevent this detrimental effect but was not able to arrest grain coarsening. There were always losses of alloying elements due to the presence of O2/CO2, but the intensity depended on the amount of titanium/niobium.