An Fe-Cr-W-V-Ti-N steel named SCRAM (super-clean reduced-activation martensitic) steel was designed for the first wall and blanket structure of fusion power plants. Compared with the Fe-Cr-W-V-Ta steel, TiN can precipitate first at 1650°C rather than TaC by the Thermal-cal Calculation. And we take vacuum induction melting (VIM) and electro-slag re-melting (ESR) together to manufacture the SCRAM steel, which can make the TiN fine and the steel pure. Mechanical properties and microstructures of SCRAM steels irradiated with single-beam (Fe) and sequential-beam (Fe plus He and Fe plus H) at 300°C were studied. The results show that, SCRAM steel can have better mechanical properties before and after irradiation while Ti was doped into the SCRAM steel. It has been reported that the precipitation formed in the steel has effect on the mechanical properties, irradiation properties and the ductile brittle transition temperature (DBTT). The effect of intermediate heat treatment on precipitation behavior and mechanical properties of SCRAM steel was investigated in order to obtain dispersed fine M23C6 carbides. The results indicated that MX carbonitrides precipitated first in the steel with intermediate heat treatment at 870°C rather than M23C6, which led to a decrease of carbon concentration in the supersaturated martensitic matrix and correspondingly a reduced volume fraction and mean size of M23C6. The intermediate heat treatment was beneficial to the mechanical properties, and proposed for reduction on the ductile brittle transition temperature (DBTT).

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