Influence of long term exposure to molten lead on the microstructure and mechanical behaviour of T91 steel

Specimens of T91 9%Cr martensitic steel were exposed to molten lead at 525 C under controlled oxygen partial pressure, for durations ranging from 6 hours to one month. At low oxygen concentration, a thin chromium oxide layer is formed; under higher concentration, the oxide layer becomes thicker and complex. Under all conditions in liquid lead, numerous porosities appear after a few days of exposure to lead in the sub-surface regions of the samples. From the residual deflection of bent samples, the stress relaxation is much faster in liquid lead than under gaseous atmosphere. However, the tensile properties remain unchanged after one month ageing in lead.