Corrosion behavior of Fe–14Cr–2W and Fe–9Cr–2W ODS steels in stagnant liquid Pb with different oxygen concentration at 550 and 650°C

Abstract

Corrosion behavior of ferritic (Fe–14Cr–2W+Y2O3) and ferritic–martensitic (Fe–9Cr–2W+Y2O3) oxide dispersion strengthened (ODS) steels in the static isothermal liquid Pb was investigated at 550 and 650°C depending on the oxygen concentration CO in the melt for duration up to 1000h. It was determined that the interaction mode of steels changes from the dissolution in the pure Pb (CO⩽10−14wt%O) to the formation of protective oxide layers on the surface of steels in the oxygen-added Pb (CO∼10−6wt%O) and to formation of multiphase non-protective scales in the Pb saturated by oxygen (CO∼10−3wt%O). In general, the observed corrosion behavior of ODS steels coincides with that of traditional chromium steels. However, specific structure of ODS steels causes some variations in corrosion process. In the pure Pb (CO⩽10−14wt%O) the fine-grained structure promotes inter-granular corrosion attack and penetration of lead into steel matrix along grain boundaries. Increase in Cr content in the steel promotes corrosion attack. In the oxygen-added Pb (CO∼10−6wt%O) the fine-grained structure, vice versa, ensures formation of oxide layers with higher Cr content due to fast diffusion of Cr into growing oxide along grain boundaries. The protective properties of oxide layers are improved with temperature rise (550→650°C) and chromium content in steel. In the oxygen-saturated Pb (CO∼10−3wt%O) the ODS steels undergo severe oxidation accompanied by the formation of non-protective multiphase scale which consist of mixture of different oxide phases: plumboferrite, magnetite, Fe–Cr spinel and free Pb. The oxidation kinetics intensifies drastically with temperature and decelerates with increasing chromium content in the steel. Based on the experimental data the scheme of interaction of components in the "steel - liquid Pb” system depending on temperature and oxygen content is proposed.