Precipitates in normalized and tempered 10%Cr ferritic/martensitic steels

Precipitates in the two 10%Cr ferritic/martensitic steels in the normalized-and-tempered condition were investigated through transmission electron microscopy with an energy dispersive X-ray system. A large number of precipitates with large difference in size and block-like, or plate/rod-like, or sphere-like morphology have been observed in the two steels. Dominant precipitate phases in the two steels were Nb-rich carbide NbC and Cr-rich carbide M23C6. Z-phases have been found in the two steels. Two types of modified Z-phases, Cr(V,Nb)(C,N), with similar chemical composition and totally different crystal structures, body-centered tetragonal and NaCl-type cubic lattices, as well as original Z-phase, CrNb(C,N), were identified in the two steels. The modified and original Z-phases were observed to coexist with a clear orientation relationship within the same precipitate particles of the steel. The formation of Z-phase in the steels has also been discussed.