Effect of silicon on ductility of T91 steel in liquid lead–bismuth eutectic environment

The tensile tests of T91 and T91Si steels at 200–450 °C in air and at 350 °C in oxygen-depleted liquid lead–bismuth eutectic (LBE) environment with strain rate of 1 × 10 –5 –5 × 10 –3 were performed. Results show that the activation energy of T91 steel is 103.45–246.76 kJ/mol and that of T91Si steel is 146.98–172.11 kJ/mol when Portevin–Le Chatelie (PLC) phenomenon occurs. The elongation reduction of T91 steel at 350 °C is not specific to LBE environment, whereas the presence of LBE promotes crack initiation and propagation and affects the elongation of the material in the necking stage. With Si addition, the elongation, especially the uniform elongation at 350 °C in LBE environment, improves, and the tendency toward crack propagation in T91 steel after slow tensile necking is reduced. The PLC phenomenon can be seen in both T91 and T91Si steels at high temperatures owing to the dynamic strain aging (DSA). The temperature ranges are different when DSA occurs, with 300–350 °C and 250–350 °C for T91 and T91Si steels, respectively.