Role of the grain orientation spread in the pitting corrosion resistance of duplex stainless steels

摘要

Duplex Stainless Steels (DSS) are highly important engineering materials due to their generally high corrosion resistance combined with high strength and moderate alloy cost (lower nickel and molybdenum content) compared to standard austenitic grades. They are widely used in various industrial sectors, such as oil & gas (pipes and storage tanks), desalination (evaporators and pumps) and pulp and paper (digester and bleaching reactors) industries. In this paper, the influence of the Grain Orientation Spread (GOS) on the corrosion resistance of DSS was investigated in sodium chloride solution. Corrosion measurements were carried out at the microscale by combining the Critical Pitting Temperature (CPT) method, the electrochemical microcell technique and a Peltier heating microstage (temperature range from -20 to 120°C ie -4 to 248℉ ). Sites were previously selected according to their GOS value. This value was calculated from the crystallographic orientation map derived from Electron Backscatter Diffraction (EBSD) measurements. The GOS gives a quantitative description of the crystallographic orientation gradients in individual grains. CPT measurements were carried out in various sites at the specimen surface: in austenite grains, in ferrite grains, at the austenite/ferrite interface with a ratio of 50/50 and in austenite grains containing extremely small ferrite grains. It has been shown that extremely small ferrite grains with a GOS value greater than 1.3°were systematically precursor sit es for pitting. The CPT range was 45-90°C (113-194℉). It was also found that other grains remaine d passive up to 100°C (212℉).