Corrosion behavior of steels in flowing lead–bismuth

Corrosion of steels in a flowing Pb–Bi environment has been studied. Specimens were exposed to the melt at 300°C and 470°C for up to 3116 h. The flow velocity was close to 2 m/s and the oxygen concentration in Pb–Bi was maintained at 1–2×10−6 wt%. Independent of the specific steels (Optifer IV, T91 and EP823 martensitic steels, 1.4970 austenitic steel), no sign of dissolution was detected for either temperatures. In all cases, a protective oxide layer was formed on the steel surface. It was very thin (thickness ≪1 μm) in the case of the 1.4970 austenitic steel, which presented the maximum resistance to oxidation in Pb–Bi–O. After 3116 h at 470°C, the thickness of the oxide layer (magnetite scale Fe3O4) formed on the martensitic steels ranged from about 10 to 20 μm. The oxidation resistance of the three martensitic steels decreases in the sequence: EP823, T91 and Optifer IV. The presence of silicon in the EP823 Russian steel (≈2 wt%) reduces the oxide layer growth. Results show that the present level of oxygen content in Pb–Bi is suitable for ensuring stable protection of steels against liquid metal corrosion at least for that period.