Review of Z phase precipitation in 9–12 wt-%Cr steels

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For high temperature applications, 9–12 wt-%Cr steels in fossil fired power plants rely upon precipitate strengthening from (V,Nb)N MX nitrides for long term creep strength. During prolonged exposure at service temperature, another nitride precipitates: Cr(V,Nb)NZ phase. The Z phases lowly replaceMX, eventually causing a breakdown in creep strength. The present paper reviews the Z phase and its behaviour in 9–12 wt-%Cr steels including thermodynamic modelling, crystal structure, nucleation process and precipitation rate as a function of chemical composition. The influence of Z phase precipitation upon long term creep strength is assessed from several different 9–12wt-%Cr steel grades and alloy design philosophies.
Original languageEnglish
JournalMaterials Science and Technology
Issue number2
Pages (from-to)126-137
Publication statusPublished - 2016


  • Z phase
  • MIX
  • 9–12Cr steels

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