The Z-phase in 9–12% Cr ferritic steels: A phase stability analysis

The formation enthalpies of the Z- and B1 MN-phases, where M = Cr, Fe, Nb, and V, were calculated using an ab initio computational method. The relative stability of the Z- and MN-phases was examined in the framework of the CALPHAD methodology. The analysis indicates that the Z-phase is more stable than the B1 MN-phase in the 9–12% Cr ferritic steels. This result is in agreement with experiments where the Z-phase is observed to dominate over the B1 MN-phases after long-term creep.