Effect of Ta and Ti on Modified Reduced Activation Ferritic/Martensitic Steels with a Thermo-mechanical Control Process

Modified reduced activation ferritic/martensitic steels with different amounts of Ta and Ti are fabricated with a thermo-mechanical control process (TMCP). TMCP greatly enhances the refinement of both the precipitates and the martensite matrix. In addition, an increase in the dislocation density is achieved. The modified steels show excellent comprehensive mechanical properties compared with traditional reduced activation ferritic/martensitic steels. In addition, under the conditions of the TMCP, the effects of Ta and Ti on the microstructure and properties are analyzed. Simply increasing the amounts of Ta and Ti does not increase the phase fraction of MX, which is quite different from that derived from equilibrium thermodynamics theory or the typical hot rolling process for traditional reduced activation ferritic/martensitic steels. Without a high enough nucleation rate for MX, the excess Ta and Ti, which are not consumed by the formation of MX, promotes the formation of proeutectoid ferrite. This decreases the impact on toughness significantly. Herein, preliminary guidance is offered for a comprehensive design with a combination of both composition and rolling processing modification for the production of reduced activation ferritic/martensitic steels.