Development of Corrosion-Resistant Duplex Stainless Steel through Controlled Thermomechanical Processing

Abstract

Duplex Stainless Steels (DSS) have gained significant importance in modern engineering owing to their exceptional combination of high mechanical strength, excellent corrosion resistance, superior weldability, and outstanding resistance to stress corrosion cracking. These properties originate from their unique dual-phase microstructure consisting of approximately equal proportions of ferrite and austenite. However, the corrosion performance and mechanical properties of Duplex Stainless Steels are highly dependent on thermomechanical processing parameters, including hot rolling temperature, deformation ratio, solution annealing temperature, cooling rate, and strain-induced phase transformations. Improper processing may lead to the formation of detrimental secondary phases such as sigma (σ), chi (χ), chromium nitrides, and carbides, resulting in chromium depletion, reduced corrosion resistance, and deterioration of mechanical performance. This research presents the development of corrosion-resistant Duplex Stainless Steel through controlled thermomechanical processing by systematically optimizing deformation and heat treatment parameters followed by comprehensive microstructural characterization and corrosion evaluation. Advanced characterization techniques including Optical Microscopy, Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Electrochemical Impedance Spectroscopy (EIS), and potentiodynamic polarization testing are employed to investigate phase evolution, grain refinement, precipitation behavior, passive film stability, and corrosion mechanisms. The investigation demonstrates that optimized thermomechanical processing promotes a balanced ferrite–austenite microstructure with refined grains, minimized secondary phase precipitation, enhanced passive film stability, and superior resistance to pitting, crevice, and stress corrosion. The findings provide valuable metallurgical guidelines for developing high-performance Duplex Stainless Steel suitable for demanding marine, chemical processing, offshore, nuclear, and structural engineering applications.