Study of Corrosion Behavior of a 2507 Super Duplex Stainless Steel: Influence of Quenched-in and Isothermal Nitrides

摘要

Precipitation of different types of chromium nitrides may occur during processing of super duplexstainless steels, affecting the properties of the material. In this study the influence of quenched-in (sizerange ca. 50-100 nm) and isothermal (size range ca. 80-250 nm) types of nitrides on the corrosionbehavior of a 2507 super duplex stainless steel has been investigated at room temperature and at 90 (above the critical pitting temperature) in 1 M NaCl solution. The microstructure has beencharacterized by scanning electron microscopy and magnetic force microscopy. The isothermalnitrides exhibit a higher Volta potential compared to the matrix, but such difference could not beobserved for the quenched-in nitrides. In-situ electrochemical AFM measurements at roomtemperature show stable surfaces for a wide range of applied potentials despite the presence of eithertype of nitrides. In the transpassive region isothermal nitrides appear to be slightly more deleteriousthan quenched-in nitrides. At 90 isothermal nitrides largely reduce the corrosion resistance of theaustenite phase, while the quenched-in nitrides reduce the corrosion resistance of the material to amuch lesser extent. The size difference between isothermal and quenched-in chromium nitrides may becrucial, in particular above the critical pitting temperature.