Effect of Aging Time on the Microstructure and Corrosion Behavior of 2507 Super Duplex Stainless Steel in Simulated Marine Environment

The effect of aging time on corrosion behavior of 2507 super duplex stainless steel (SDSS) under a 3.5wt.% NaCl solution was explored by electrochemical tests, atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and immersion test. The experimental results indicate that with an increasing aging time, the anti-corrosion property of 2507 SDSS aged at 850 °C decreases significantly. The SDSS aged for 5 min contains two precipitated phases (χ, γ2). As aging time increases, the quantity of σ phase precipitates significantly increases, which seriously reduces the corrosion resistance of SDSS due to the increasing number of micro-galvanic corrosion cells. In addition, the passive film of SDSS aged for 60 min exhibits the minimum values of Rct and Rf, as well as the maximum carrier densities. For the aging time of 5 min, the passive film consists of higher contents of Cr2O3 and H2O, as well as less FeO, while also demonstrating good stability and compactness. The precipitated phases seriously decrease the protective ability of passive film, especially the σ phase.