Investigation of the liquid metal embrittlement sensitivity of a low Ni alumina forming austenitic steel in presence of liquid lead bismuth eutectic

The liquid metal embrittlement (LME) sensibility by liquid lead bismuth eutectic (LBE) of a low Ni Alumina Forming Austenitic (AFA) steel designed as structural material for Lead Fast Reactor has been studied. To investigate the LME sensitivity by liquid LBE, tensile tests in air and in liquid LBE have been carried out between 350 °C and 550 °C, at 5×10 -5 and 5×10 -6 s -1 . Then analyses of fracture surfaces, cracking and damage have been performed by SEM-EDS-EBSD. The AFA steel is not sensitive to LME at 350 °C but suffers from LME at temperatures above 450 °C. The liquid LBE promotes intergranular surface cracking, propagation of intergranular cracks and in the most detrimental conditions, ferritization with the selective loss of Ni, Mn and Cu. The highest temperature and the lowest strain rate promote the LME sensitivity. Then, no ductility trough, followed by the ductility recovery at high temperature, is observed. The LME of the low Ni AFA steel could be mainly explained by the Gordon-An model. Because of the intrinsic transgranular ductility of the steel, grain boundary engineering appears to be the key point to defining, in the future, a low-Ni AFA steel that is not susceptible to LME in presence of liquid LBE.