Wetting and mechanical properties, a case study: Liquid metal embrittlement of a martensitic steel by liquid lead and other liquid metals

We present experimental results of tensile and fatigue properties of the T91 (a 9% Cr martensitic steel) in a stagnant molten metallic bath (Pb, Pb-Bi or Sn for instance). Under particular experimental conditions, the tensile tests revealed an instantaneous embrittlement of the material, more pronounced at low temperature, that disappears as the temperature is raised above 450°C. This behavior is explained by the reduction of the surface energy of the bare metal induced by the adsorption of the liquid metal. When the steel is submitted to low cycle fatigue tests in presence of the liquid Pb-Bi eutectic at 300°C, its lifetime is significantly reduced compared to tests performed in air. In this case, given the complexity of the mechanisms leading to a fatigue fracture, it is more difficult to ascribe the observed embrittlement to the sole surface-energy reduction effect, but and adsorption-induced localization of the plastic deformation at the very crack tip is an appealing hypothesis.