Applications of electrochemical methods for investigations of localized corrosion of nitrogen-molybdenum stainless steels

Electrochemical methods were used to determine the localized corrosion resistance of 12 austenitic stainless steels (SS) with a composition range of 22%Cr-5%Ni-5%Mn-(1% to 5%)Mo-(0.0% to 0.7%)N-balance Fe in a deaerated 3.5 wt% sodium chloride (NaCl) solution from 10degreesC to 97degreesC. Potentiodynamic polarization was used to determine the critical pitting potential (CPP), protection potentials, and polarization resistance (R-p), and potentiostatic cyclic thermometry was used to determine the critical pitting temperature (CPT) and critical crevice temperature (CCT). The results of potentiodynamic polarization showed that all of the SS containtng both N and Mo have CPP significantly higher than either Type 304 (UNS S30400) or Type 316L (UNS S31603) SS. R, correlated with the pitting resistance equivalent (PPE) for PRE from 20 to 45; however, for PPE > 45 there was no correlation. Results obtained by potentiostatic cyclic thermometry showed that CPT and the CCT are both linear functions of ME. and strongly dependent on both Mo and N concentration in the alloy.