On the role of Nb in Z-phase formation in a 12% Cr steel

Z-phase precipitation in two model alloys, 12CrVNbN and 12CrVN, has been investigated. The alloys were aged up to 104 h and their precipitate evolution was followed by X-ray diffraction and transmission electron microscopy. The formation rate of Z-phase from vanadium-based nitrides, (V,Nb)N, in the Nb-containing alloy was observed to proceed considerably faster than in the Nb-free alloy. A hypothesis is put forward that explains the enhanced stability of VN in terms of changes in the interfacial energy of VN with the ferrite matrix.