Effect of temperature on the interaction of ÉP823 steel with lead melts saturated with oxygen

We study the corrosion behavior of ferritic-martensitic ÉP823 steel in a static lead melt, saturated with oxygen, at 550 and 650°C. At these temperatures, a complex magnetite-base scale is formed on the surface of steel, but the mechanisms of its growth are different. At 550°C, corrosion has a cyclic character. On the surface of steel, a Fe^sub 1+x^Pb^sub 2-x^O^sub 4^-Fe^sub 1+x^Cr^sub 2-x^O^sub 4^ two-layer scale is formed periodically. Reaching the critical thickness (18 µm), it exfoliates along the interface with the matrix, to which oxygen-containing lead penetrates, whereupon this process is repeated. The corrosion rate is 0.08 mm/year. At 650°C, the intensification of reactions of formation of chromium spinel and plumboferrite induces the growth of a porous scale, where lead is accumulated. This scale has good adherence to the matrix and is formed as a compact conglomerate owing to the efficient mass transfer at all interfaces, which leads to a catastrophic rate of thinning of the specimen (3.82 mm/yr) in a lead melt. On the basis of experimental data, we propose schemes of the oxidation of chromium steels in a lead melt with a high oxygen activity at different temperatures.