Phase (matter)

Metallurgy

Materials science

Layer (electronics)

Precipitation

Creep

Thermodynamics

Physics

Organic chemistry

Alloy

Microstructure

Composite material

Chemistry

Meteorology

Nitride

Nucleation

Materials Science and Technology

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)N Z phase. The Z phases lowly replace MX, 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.

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