Stability of Z-phase and M6X in creep-resistant steels

The effect of two levels of niobium (0.1 and 0.3 wt.% Nb) in AISI 316LN austenitic steels and intentional additions of nickel (0.5 and 1.15 wt.% Ni) to 12CrMoVNbN martensitic steels on precipitation reactions was studied. Minor phase evolution at temperatures of 475–650 °C was studied on creep ruptured specimens with times to rupture extending up to 220,000 h. The dependence of the thermodynamic and dimensional stability of nitrogen-rich Z-phase and M6X (Cr3Ni2SiX-type) precipitates on the chemical composition of steels and the temperature of exposure was investigated.