The Effect of Alloying Elements on the Repassivation Potentials for Crevice Corrosion of Stainless Steels in 3% NaCl Solution

Abstract

Repassivation potentials, ER, CREV, for metal/metal-crevices of 54 kinds of stainless steels were measured in 3% NaCl solution at 80°C. Obtained ER, CREV values were analysed in relations to chemical compositions of the 52 steels into multiple linear regressions in the form of Y=b0+∑bjXj for every one of steel groups, which are α (ferritic, 15 steels), α+γ (duplex, 11 steels), γ (austenitic, 18 steels with Cu<0.4%) and γCu (austenitic, 8 steels with 0.9-3.5% Cu). Y is the predicted value for ER, CREV and Xj denotes the content of alloying element j in wt% except j=Ni where Xj=logNi. Alloyed Cu more than 2% to austenitic steels changes the value of blogNi from -97mV/decade for γ to +45mV/decade for γCu-group steels. Well known beneficial effects of Mo were confirmed for all groups of steels except the γCu-group steels containing 2-3% Cu, of which ER, CREV values are kept constant independently on Mo contents. Addition of N up to 0.2% were found to be beneficial for the duplex steels, but not significant for the austenitic steels in spite of beneficial effects of N reported on pitting potentials.