Embrittlement of a martensitic steel by liquid lead

Abstract

EDF-EMA, Centre des Renardie`res, B.P. No. 1, Ecuelles-77250 Moret-sur-Loing, France(Received April 10, 1999)(Accepted in revised form June 23, 2000)Keywords: Liquid metal embrittlement; Martensitic steels; Lead; Mechanical propertiesIntroductionLiquid metal embrittlement refers to the reduction of ductility of an otherwise ductile material whenstressed in contact with a liquid metal. This general statement does not presuppose anything about theactual microscopic mechanism that leads to LME, i.e. whether the embrittlement is a consequence ofgrain boundaries penetration and/or wetting which induces necessarily intergranular fracture or whetherit is the result of a reduction in cohesion that can either lead to inter or to transgranular fracture. Anotheraspect of LME usually mentioned is its specificity, which means that only some particular liquidmetal-solid metal couples are prone to embrittlement. Such specificity has been recently questioned byFernandes and Jones [1] who suggest that it may rely on particular testing conditions rather than on theactual interactions between the liquid and the solid metal. In this paper we report preliminary results ofLME of a martensitic steel by liquid lead. Our data strongly suggest, that under the experimentalconditions adopted, LME is not due to grain boundaries penetration or wetting, and instead may beinterpreted in the framework of the more traditional mechanisms that suppose a reduction of surfaceenergy and/or bond-strength induced by liquid lead adsorption (see for instance the review article of Old[2] and references therein). In addition, the work presented here clearly demonstrates that embrittlementis observed for particular metallurgical and mechanical conditions. When these are not fulfilled, liquidlead has no apparent detrimental effect, a fact that would have led to the wrong conclusion that thereis no LME of the steel by liquid lead.ExperimentalTensile specimens 4mm in diameter and 20mm in gauge length were machined from a 9% Cr 1% Molabelled 91 grade supplied by Creusot Loire Industrie. Its chemical composition is summarised in Table1. Two different sets of samples have been used, i) the as received ones (R type in the following) which