Pitting corrosion behavior of cerium treated HSLA steel induced by sulfide inclusions in 3.5 wt% NaCl solution

Pitting corrosion behavior of Ce treated HSLA steels induced by sulfide inclusions in 3.5 wt% NaCl solution was investigated with potentiodynamic polarization and immersion corrosion test. The results show that Ce added steels exhibit better pitting corrosion resistance with lower corrosion current density and bigger pitting potential compared with steel without Ce, which is mainly attributed to optimized characteristics of spherical Ce-oxysulfide inclusions with less number density, smaller average size and lower pitting corrosion susceptibility. The spherical Ce2O2S inclusions precipitated on the surface of CeAlO3 inclusions in the Ce added steels induce pits with bigger opening mouth and shallow depth, reducing their tendency of extension to go deeper due to occlusion corrosion battery in the pitting holes. Furthermore, corrosion inhibitor Ce(OH)(3) generated by Ce2O2S hydration can weaken electrochemical corrosion of the matrix micro-region around the pits. To avoid harmful bigger inclusions, Ce content in steels should be regulated within reasonable range, 0.015 wt% Ce in present steels effectively modified inclusions to acquire the best pitting corrosion resistance of the steels. (C) 2020 Published by Elsevier B.V. on behalf of Chinese Society of Rare Earths.