Effect of Ti addition on hardness change during tempering in reduced activation ferritic/martensitic (RAFM) steels

The specificities of hardness change during tempering in Ti-containing reduced activation ferritic/martensitic (RAFM) steels were found while developing new RAFM steels with improved mechanical properties. Hardness decline during tempering of RAFM steel where Ti replaced Ta (Ti-RAFM) and RAFM steel with both Ta and Ti (TaTi-RAFM) was greater than that in conventional RAFM steel with Ta (Ta-RAFM). It is believed that Ti addition tend to accelerate the growth of MX precipitates and thereby accelerated diffusion of carbon from the martensite matrix, leading to a large decrease in hardness of martensite in Ti-containing RAFM steels during tempering. •The hardness decline during tempering in Ti-RAFM or TaTi-RAFM where Ti was added is due to the decrease in carbon remaining in martensite resulting from fast growth of TiC precipitates in Ti containing RAFM compared to TaC precipitates in Ta-RAFM.