Conversion of MX nitrides to Z-phase in a martensitic 12% Cr steel

L. Cipolla, Hilmar Kjartansson Danielsen, D. Venditti, P.E. Di Nunzio, John Hald, Marcel A. J. Somers

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A 12% Cr model steel was designed with the purpose of studying the nucleation and growth of modified Z-phase, Cr(V,Nb)N. The model alloy develops Z-phase after relatively short ageing times and contains only nitrides of Cr, V and Nb. Interferences from the presence of carbides and the development of Laves phase were avoided by keeping the C, W and Mo contents as low as possible. Transmission electron microscopy and X-ray diffraction analysis of extracted particles were used to follow the evolutions of phase composition, phase morphology and phase fraction, particularly of the precipitation of Z-phase, during ageing at 600, 650 and 700 degrees C for up to 103 h. The development of Z-phase appears to be accomplished by the diffusion of Cr atoms into (V,Nb)N particles and their subsequent conversion into cubic or tetragonal Z-phase. Studies at various temperatures indicate that Z-phase development proceeds fastest at 650 degrees C and that Z-phase forms faster at prior austenite grain boundaries.
Original languageEnglish
JournalActa Materialia
Issue number2
Pages (from-to)669-679
Publication statusPublished - 2010


  • TEM
  • Nitrides
  • Heat resistant steels
  • Phase transformation kinetics
  • XRD


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