Mechanical behaviour of the T91 martensitic steel under monotonic and cyclic loadings in liquid metals

The paper deals with the mechanical properties in liquid metals of the T91 martensitic steel, a candidate material for the window of an accelerating driven system (ADS). Two main questions are examined, the risk of liquid metal embrittlement and the accelerated fatigue damage by a liquid metal. It is found that the transition from ductile to brittle behaviour induced by a liquid metal is possible as a result of a decrease in surface energy caused by the adsorbed liquid metal. The embrittlement can occur only with a hard microstructure and a nucleation of very sharp defects inside the liquid metal. Under cycling straining, the fatigue resistance of the standard T91 steel is decreased by a factor of about 2 in the liquid metal as compared to air. It is proposed that short crack growth is promoted by the liquid metal which weakens the microstructural grain boundary barriers and skip the microcrack coalescence stage.