Role of Al addition and Y2O3 on the intergranular corrosion behavior of AFA-ODS steel in the supercritical water

Abstract

A new alumina-forming austenitic oxide dispersion strengthened steel was prepared, and the general corrosion behavior was studied. The results showed that the Y2O3 addition reduced the grain size. With small grains, the grain boundary density increased, which accelerated the formation of stable oxide scale in the corrosion process and obviously decreased the weight gain of AFA-ODS steel. A four-layer oxide scale was formed on the both sides of grain boundary in the inner layer, and a Cr-depletion and metallic Ni layer were formed at the oxide/matrix interface. The upper part of inner layer had many cavities. Al2O3 protective layer appeared in the inner oxide layer and the corrosion degree of the underlying material was reduced. Grain boundary migration was also induced by the element diffusion. The structure surrounding Y2O3 particles in the inner layer was affected slightly by Y2O3 particles. Y2O3 particles at the oxide/matrix interface could promote the corrosion and caused the sunken corrosion pits because the element could diffuse easily through the interface between Y2O3 particles and the material. However, with the addition of Al, Al could diffuse into the sunken pits and wrapped Y2O3 particles, which inhibited the further development of the sunken pits.

Keywords

• Supercritical water
• ODS steel
• Intergranular corrosion
• Al addition
• Dispersive Y2O3