On the crystal structure of Z-phase Cr(V,Nb)N

The Z-phase Cr(VNb)N particles in various 9 to 12 pct Cr creep-resistant steels were investigated with electron diffraction, energy dispersive spectroscopy (EDS), and electron energy loss spectroscopy (EELS). In addition to the well-known tetragonal crystal structure for Z phase, a cubic crystal structure was identified for Cr(V,Nb)N and CrVN particles, but not for CrNbN. The tetragonal and cubic crystal structures were observed to coexist within the same particles, and the orientation relationship between the two lattices was determined. Understanding and controlling the nucleation of Cr(VNb)N particles could be of crucial importance to enable improvement of the long-term creep stability of 9 to 12 pct Cr martensitic steels.