The fracture of austenitic and martensitic steel in liquid lithium

Abstract

The austenitic steel 1.4301 (X5 CrNi 189) and the two ferritic steels 1.4914 and 1.4923 (X18 CrMoVNb 121, X22 CrMoV 121) have been tensile tested in liquid lithium in order to get information about the mechanical properties of these alloys in liquid alkali metal environment. Specimens have also been tested in lithium and in air after a pre-exposure in lithium for 1000 h at a temperature of 550°C. The results of the tensile tests indicate that the austenitic steel is insensitive to lithium environment, when not pre-exposed to this medium before. After a pre-exposure the specimens fail in a brittle manner when tested in lithium, and in a ductile manner when tested in air. The behaviour of the two ferritic steels can be regarded as quite similar when compared to each other. The tests indicate that the steels are affected in their tensile properties even without a pre-exposure (lower ductility, brittle/shear mixed fracture mode). The reactions of the lithium are due to grain boundary effects in all steels tested. These effects are determined by the metallurgic state of the grain boundaries. The observed LME effects might be of technical significance during the procedures of starting and interrupting the reactor operation, when the critical temperature ranges are passed. The material behaviour under operating conditions of a blanket at temperatures of 400–500°C and with creep deformation should not be influenced to that degree.