Investigation on microstructure evolution, mechanical properties and corrosion resistance of dual phase stainless steel joints welded by GTAW and SAW methods

Abstract

Duplex Stainless Steels (DSSs) have excellent mechanical properties and corrosion resistance thanks to the biphasic ferritic-austenitic microstructure. This microstructure feature is highly influenced by the welding heat cycles. In this research paper, the effect of gas tungsten arc welding (GTAW) and submerged-arc welding (SAW) on the microstructure, mechanical and corrosion properties of SAF 2507 duplex stainless steel (DSS) were investigated. The base metal had the austenite content of 45 %, while the weld metals show variation of austenite contents in different regions. The middle regions of the both welds (GTAW ∼ 60.5 %, SAW ∼ 49.3 %) showed higher austenite contents than that of the root (GTAW ∼ 25.6 %, SAW ∼ 40.9 %) and top (GTAW ∼ 44.2 %, SAW ∼ 34.2 %) regions. Subsequent heat cycles promoted the precipitation of austenite from the primary ferrite, resulting in the higher contents of austenite in the middle welds. The nanoindentation tests revealed the individual properties of the typical phases, i.e., γ-Fe ∼ 5.4 GPa and α-Fe ∼ 4.7 GPa in both weld metals. The average tensile strength of GTAW and SAW welded joints are 997 MPa and 1109 MPa, respectively. The corrosion behavior of the weld metal was also evaluated through potentiodynamic polarization curves. The as-welded joints exhibit slight decrease in corrosion resistance, as compared to the base metal. These two weld metals showed slightly difference in mechanical and corrosion resistance properties. SAW method is most recommended when large thickness or high efficiency welding is required.