Role of rare earth elements on the improvement of corrosion resistance of micro-alloyed steels in 3.5 wt.% NaCl solution

Abstract

The effects of rare earth (RE) addition on the corrosion behavior of micro-alloyed steels in 3.5 wt.% NaCl solution were investigated elaborately through electrochemical tests and material characterization analyses. Results showed that the corrosion rate decreased after addition of RE elements. The RE elements did not alter the pitting nucleation mechanism, while the sensitivity of pitting propagation was reduced by decreasing the pitting density and pitting depth. In the long-term corrosion, preferential precipitation of RE corrosion products promoted the formation of protective rust layers and accelerated the co-deposition of these layers, which probably be favorable for the formation of compact rust layers. Moreover, the RE addition reduced the surface electrochemical activity and the adsorption tendency of Cl− on the metal surface. As a consequence, the resistance of electrochemical reactions (represented by Rp values in EIS tests) increased, resulting in a decrease of corrosion rate by RE addition.