Effects of W substitution on the precipitation of secondary phases and the associated pitting corrosion in hyper duplex stainless steels

Abstract

To elucidate the effects of W substitution on the precipitation of secondary phases and associated pitting corrosion in hyper duplex stainless steels, potentiodynamic polarization test, a SEM–EDS analysis and thermodynamic calculation were conducted. W substitution for Mo to the base alloy reduces the total amount of secondary phases. Particularly, W substitution alloy results in pronouncedly suppressing the amount of sigma phase whereas it slightly increases chi phases. W substitution alloy retards the deterioration of resistance to pitting corrosion by the precipitation of secondary phases due to delayed precipitation of the secondary phase. Experimental results are compared with calculations of alloying elemental activities. The thermodynamic calculations for the precipitation of secondary phases were in good agreement with the experimental results.