Effects of Ti Addition on the Microstructure and Tensile Properties of China Low Activation Martensitic Steel for Nuclear Fusion Reactors

Herein, the effects of Ti, a low activation alloying element, in the range of 0.01-0.11 wt% on the microstructure, mechanical properties, and impact toughness of China low activation martensitic steel are studied. Fine prior austenite grains and some delta-ferrite phases are observed for alloys with a Ti content of 0.05 and 0.11 wt%, respectively. The 0.05Ti alloy exhibits a higher yield strength (YS) compared with the 0.01Ti and 0.11Ti alloys because of the additional precipitation hardening by the fine MX particles and small grain size. When the samples are tempered at 650 degrees C, nanosized (Ti, W) C MX carbides with a size of approximately 20 nm precipitate, leading to an increase in the ultimate tensile strength (UTS) and YS of the 0.05Ti alloy. The ductile-to-brittle transition temperature (DBTT) decreases when the Ti content increases to 0.05 wt%. However, the DBTT of the 0.11Ti alloy increases with the precipitation of the delta-ferrite phase. On the basis of the performance of the steels, the optimal Ti content is found to be approximately 0.05 wt% and the optimal tempering temperature is found to be 650 degrees C.