Abstract
In this study, 2205 duplex stainless steel was friction-stir-welded at different welding speeds. The microstructural characteristics such as grain sizes, grain boundary misorientation angles, and phase contents in the stir zones of the joints were detected. The potentiodynamic polarization and electrochemical impedance spectroscopy were also measured to evaluate the corrosion property of the stir zones. The effects of the microstructures on the corrosion property for friction-stir-welded 2205 duplex stainless steel were analyzed. The results indicated that the FSW process refined the grains and increased the ferrite contents in the stir zones. With increasing the welding speed from 30 mm/min to 50 mm/min, the grain size in the stir zone decreased from 1.64 μm to 0.96 μm, the ferrite content decreased from 59% to 54.4%, and the fractions of low angle grain boundaries for austenite and ferrite phases decreased from 63.9% and 92.6% to 18.0% and 41.1%, respectively. In this study, the effect of grain size on the corrosion resistance was the most significant and it was followed by the phase composition and the grain boundary misorientation angle. The stir zone obtained at 50 mm/min has the highest corrosion resistance, and it is followed by the base material and the stir zone obtained at 30 mm/min.
Highlights
Duplex stainless steel (DSS) whose microstructure consists of appropriately balanced ferrite (α) and austenite (c) phases has been widely applied owing to its high mechanical and corrosion properties [1]
Abubaker et al [7] used friction stir processing to improve the microstructure and mechanical properties of 2207 DSS. e results indicated that grains were refined from a size of 160 μm to 2∼30 μm in the processed zone and the strength, hardness, and fracture toughness of the material were increased by 14%, 11%, and 12%, respectively
2205 DSS plates with 4 mm thickness were used as the base material, the chemical compositions of which are listed in Table 1. e plates were machined into rectangular welding samples with dimension of 300 mm length by 100 mm width
Summary
Duplex stainless steel (DSS) whose microstructure consists of appropriately balanced ferrite (α) and austenite (c) phases has been widely applied owing to its high mechanical and corrosion properties [1]. Friction stir welding (FSW) is a solid-state welding technology [2] In this welding process, the welded metal is not melted; as a result, the balanced phase composition can be maintained and the precipitation of sigma phase can be restrained [3]. Some studies on FSW of DSS have been carried out and they were mainly related to welding process, joint microstructure, and mechanical properties [4, 5]. Wang et al [6] studied the effect of the tool rotation speed on the microstructures and mechanical properties of the FSW joint of 2205 DSS. Because the phase transformation of DSS will significantly affect the material mechanical and corrosion properties, some studies on the phase composition of FSW joint were carried out. Particular attention was paid to the relationship between microstructure and corrosion resistance of the SZs
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