Effects of Tungsten on the Precipitation Kinetics of Secondary Phases and the Associated Susceptibility to Pitting Corrosion in Duplex Stainless Steels

Abstract

Effects of tungsten (W) on the precipitation kinetics of secondary phases and the associated resistance to pitting corrosion of 25 % Cr duplex stainless steels were investigated through microstructural and electrochemical noise analyses. With the partial substitution of W for Mo in duplex stainless steel, the potential and current noises of the alloy were significantly decreased in chloride solution due to retardation of the σ phase precipitation. The preferential precipitation of the χ phase in the W-containing alloy during the early period of aging contributed to retarding the precipitation of the σ phase by depleting W and Mo along grain boundaries. In addition, the retardation of the nucleation and growth of the σ phase in the W-containing alloy appears to be attributed to the inherently low diffusivity of W compared with that of Mo.