Abstract
This study investigates the microstructure, mechanical properties, and corrosion resistance of a friction-stir-welded joint of the hyper duplex stainless steel SAF2707. Friction stir welding (FSW) is performed at a tool rotation rate of 400 rpm and a welding speed of 100 mm/min. The microstructure of the joints is examined using scanning electron microscopy and X-ray diffraction. Tensile test and fractography are subsequently employed to evaluate the mechanical properties of the joints. Results show that the grain size of the stir zone (SZ) is smaller than that of the base metal (BM). Electron back-scattered diffraction analysis reveals that fine-equiaxed grains form in the SZ because of the dynamic recrystallization during the FSW. These grains become increasingly pronounced in the austenite phase. The tensile specimens consistently fail in the BM, implying that the welded joint is an overmatch to the BM. Moreover, the welded joints consist of finer grains and thus display higher tensile strength than their BMs. Potentiodynamic polarization curves and impedance spectroscopy both demonstrate that the corrosion resistance of the SZ is superior to that of the base material.
Highlights
Given the favorable combination of mechanical and corrosion properties and excellent weldability of duplex stainless steels (DSSs), DSSs have become more attractive than austenitic and ferritic stainless steels in terms of applications [1,2]
The welding surface is smooth, and macroscopic cracks, air holes, and tunnel defects are absent along the welding line, indicating that the welding parameter can produce sufficient heat input to ensure the flow of plastic materials
4a), the left and right sides of the joint center comprise the joint subjected to Friction stir welding (FSW)
Summary
Given the favorable combination of mechanical and corrosion properties and excellent weldability of duplex stainless steels (DSSs), DSSs have become more attractive than austenitic and ferritic stainless steels in terms of applications [1,2]. The corrosion resistance of DSSs is determined by the fraction of α, γ, and detrimental intermetallic phases, such as σ, which often renders Cr- and Mo-depleted zones susceptible to high-rate dissolution [5,6,7] Given their inherent brittleness, these undesirable intermetallic phases, which form during hot rolling or welding, often degrade the mechanical properties of DSSs [8,9]. Studies have shown that FSW considerably affects the mechanical properties and corrosion resistance of DSSs during welding. In this study, HDSS is welded using FSW to investigate the microstructure, mechanical properties, and resistance to corrosion of HDSSs that underwent FSW. In this diagram, the welding surface is smooth, and macroscopic cracks, air holes, and tunnel defects are absent along the welding line, indicating that the welding parameter can produce sufficient heat input to ensure the flow of plastic materials.
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