Composition design of reduced activation ferritic/martensitic (RAFM) steels based on cluster structure model

The composition characteristics of reduced activation ferritic/martensitic (RAFM) steels were investigated using a cluster-plus-glue-atom model. The basic cluster formula [Cr-Fe₁₄](Cr_0.5Fe_0.5) was determined, where the cluster part [Cr-Fe₁₄] is a rhombic dodecahedron centered by Cr and surrounded by 14 Fe atoms. According to the principle related with self- consistent magnification of cluster formula and similar element substitution, two multi-component alloys were designed by adding V, Mn, Mo, W, Nb and C into [Cr-Fe₁₄](Cr_0.5Fe_0.5) i.e.[Cr₁₆Fe₂₂₄](Cr₈(V, Nb, Mn, Mo, W, Fe)₈) and {[Cr₁₆Fe₂₂₄](Cr₈(V, Nb, Mn, Mo, W, Fe)₈)}C₁. Alloy rods with a diameter of 6 mm were prepared by copper mould suction casting method, then normalized at 1323 K for 0.5 h and tempered at 1023 K for 1 h, both followed by water-quenching. The experimental results revealed that the substitutional solid solution alloys without C exhibit a monolithic ferrite microstructure and that of the other serial alloys with C varies with alloying elements and their contents. The microhardness (HV) of alloys changes with microstructures, and furthermore, while the HV of substitutional solid solution alloys decreases monotonously with the increase of the valence electron concentration per volume VEC/R_a³.