Effects of Sulfur Addition on the Formation of Inclusions and the Corrosion Behavior of Super Duplex Stainless Steels in Chloride Solutions of Different pH

Effects of sulfur addition on the formation of inclusions and the corrosion behavior of super duplex stainless steels in chloride solutions of different pH were investigated using potentiodynamic and potentiostatic polarization techniques. As sulfur content increased, the corrosion resistance decreased due to the formation of numerous manganese sulfides deteriorating the corrosion resistance. The solutions used for this study are NaCl and NaCl + HCl solutions. The corrosion behavior is dominated by the pitting corrosion in NaCl solution of pH 7 and by both uniform and pitting corrosion in NaCl + HCl solution of pH 1. The pitting corrosion of the alloys was initiated at all types of inclusions of manganese sulfides, manganese oxy-sulfides and manganese oxides and then propagated to the ferrite phases, and finally propagated to the austenite phases. [doi:10.2320/matertrans.M2012194]