Evaluation of the mechanical properties of T91 steel exposed to Pb and Pb–Bi at high temperature in controlled environment

It is known that liquid metal embrittlement (LME) is strongly dependent on a so-called `intimate contactʹ between the solid and liquid metal (LM) phases. This point is emphasised in this paper aimed at determining suitable contact conditions to favour LME of T91 steel after short exposure to stagnant molten Pb or Pb–55%Bi. The temperature range (T∼540°C) is high with respect to the expected operating conditions of spallation targets. We determine three temperature cycles, in pure lead or lead–bismuth under flowing He–4%H2 for LME testing. Good contact is obtained between T91 and Pb–Bi, but poor contact between T91 and Pb. Accordingly, the T91 steel tensile properties are not degraded by Pb, but modified after exposure to Pb–Bi. In such case, rupture of the test bar occurs in regions where Pb–Bi is `adherentʹ onto the steel. The rupture facies is not fully ductile as for T91 in Pb.