Influence of W and Ta content on microstructural characteristics in heat treated 9Cr-reduced activation ferritic/martensitic steels

This study aims at understanding the microstructural changes due to variation of W and Ta content and heat treatment in 9Cr-W-Ta-0.2V-C reduced activation ferritic/martensitic steels, with W and Ta concentrations varied from 1 to 2 wt.% and 0.06 to 0.14 wt.% respectively. An increase in concentration of W and Ta in the steels refined prior austenite grain size and lath width, though the change was not significant beyond 1.4 wt% W. Increase in W and Ta concentrations also resulted in a decrease in size and increase in number density of carbides on tempering. Microchemical analysis of M23C6 precipitates in tempered steel showed enrichment of W with increase in W content of the steel, whereas addition of Ta showed no significant change in chemistry of M23C6 or MX, but only increased the number density of fine MX precipitates.