Effect of Grain Size on the Pitting Corrosion Resistance of Lean Duplex Stainless Steel

The effects of grain refinement on the resistance to pitting corrosion and passive film properties of lean duplex stainless steel (Fe-18.28Cr-5.68Mn-2.38Mo-0.39W-0.30N-0.035C, wt%) are studied. For this purpose, the grain size of this alloy is adjusted to 3, 7, and 17 mu m through an annealing process after cold rolling. The pitting corrosion resistance is evaluated through potentiodynamic polarization tests in aqueous solutions containing Cl-. The grain size reduction enhances the resistance to pitting corrosion of the alloy. Mott-Schottky analysis and X-Ray photoelectron spectroscopy analysis on the passive films show that, as the grain size decreases, the density of point defects of the film decreases, the film thickness increases, and the cation fraction of Cr of the film increases. The improved resistance to pitting corrosion by grain refinement is attributed to the formation of the thick and dense passive film with a high Cr content.