Embrittlement of the martensitic steel 91 tested in liquid lead

Two potential problems are encountered in the case of intimate contact betw een liquid metals and metallic substrates: grain boundary wetting and liqui d metal embrittlement (LME) which both induce a degradation of the mechanic al properties. Tensile tests were carried out on a 9% Cr 1% Mo martensitic (Grade 91) steel in a liquid lead environment at temperatures ranging betwe en 623 and 773 K. The Grade 91 steel was submitted to heat treatments in or der to modify its hardness and also to produce either ferritic or martensit ic grains. Smooth and notched specimens were used. We found out that by com bining adapted heat treatments and the notch effect, it is possible to crea te conditions severe enough that lead to LME. Our experimental observations (trans-ranular failure) are compatible with the expectations of traditiona l mechanisms based on a reduction of the surface energy and/or adsorption i nduced chemical bond softening at the steel surface in contact with liquid lead. (C) 2001 Elsevier Science B.V. All rights reserved.