Friction Stir Welding of 2205 Duplex Stainless Steel: Feasibility of Butt Joint Groove Filling in Comparison to Gas Tungsten Arc Welding

Abstract

This work investigates the feasibility of using friction stir welding (FSW) process as a groove filling welding technique to weld duplex stainless steel (DSS) that is extensively used by petroleum service companies and marine industries. For the FSW experiments, three different groove geometries without root gap were designed and machined in a DSS plates 6.5 mm thick. FSW were carried out to produce butt-joints at a constant tool rotation rate of 300 rpm, traverse welding speed of 25 mm/min, and tilt angle of 3o using tungsten carbide (WC) tool. For comparison, the same DSS plates were welded using gas tungsten arc welding (GTAW). The produced joints were evaluated and characterized using radiographic inspection, optical microscopy, and hardness and tensile testing. Electron back scattering diffraction (EBSD) was used to examine the grain structure and phases before and after FSW. The initial results indicate that FSW were used successfully to weld DSS joints with different groove designs with defect-free joints produced using the 60° V-shape groove with a 2 mm root face without root gap. This friction stir welded (FSWed) joint was further investigated and compared with the GTAW joint. The FSWed joint microstructure mainly consists of α and γ with significant grain refining; the GTWA weld contains different austenitic-phase (γ) morphologies such as grain boundary austenite (GBA), intragranular austenite precipitates (IGA), and Widmanstätten austenite (WA) besides the ferrite phase (α) in the weld zone (WZ) due to the used high heat input and 2209 filler rod. The yield strength, ultimate tensile strength, and elongation of the FSWed joint are enhanced over the GTAW weldment by 21%, 41%, and 66% and over the BM by 65%, 33%, and 54%, respectively. EBSD investigation showed a significant grain refining after FSW with grain size average of 1.88 µm for austenite and 2.2 µm for ferrite.

Microstructure and Mechanical Properties of Friction Stir Welded 2205 Duplex Stainless Steel Butt Joints

“…It can be noted that the present phases α and γ in the BM are 50.4% and 49.6%, respectively. These values are close to that reported by other authors for the as-received DSS 2205 [1,7]. In addition, from Table 5, the α: γ phase ratio for the welded butt joint at 600 rpm, 50 mm, and 14 kN is 49.4:50.6, while the joint welded at 300 rpm, 25 mm/min, and 20 kN has a ratio of 48.0:52.0.…”

“…This groove-like defect can surely degrade the tensile properties of the weld joint. Some works [1,32] reported that groove-like defects are primarily generated with insufficient heat input during the stirring process. In this condition, the plastic material could not easily flow in the SZ to build the sound butt joint by the tool pin.…”

“…It is well established that 2205 duplex stainless steel (2205 DSS) has almost equal austenitic (γ-phase) and ferritic (α-phase) phases. It is increasingly used in many engineering applications as an alternative to austenitic and ferritic stainless steel because of its good combination of high strength and corrosion resistance [1][2][3]. The 2205 DSS has been extensively used in the petrochemical and marine industries [4,5].…”

“…The α-phase allows high strength besides corrosion resistance, whereas the austenite influences ductility [10,11]. The microstructural changes of the 2205 DSS welded joints using the fusion welding technique showed undesirable features due to the composition of filling rod materials and temperature variation during the thermal welding cycle [1,12,13]. This leads to a loss in mechanical properties and corrosion resistance.…”

“…They also concluded that the microstructures features and mechanical properties are related to the processing parameters. Recently, Ahmed et al [1] investigated the applicability of FSW as a new welding method to groove filling 2205 DSS instead of the gas tungsten arc welding (GTAW) technique. They reported that the yield strength (YS), ultimate tensile strength (UTS), and elongation (E%) of the FSWed joints are enhanced over the GTAW joints by 21%, 41%, and 66%, respectively.…”