Investigations on coarsening of MX and M23C6 precipitates in 12% Cr creep resistant steels assisted by computational thermodynamics

Coarsening of MX and M23C6 precipitates in two 12% Cr high alloyed steels have been investigated at creep conditions of 650 °C, 100 MPa up to 10,000 h. The evolution of precipitates at different creep times was determined experimentally using scanning transmission electron microscopy (STEM). Phase equilibria were calculated with Thermocalc and simulations of coarsening of precipitates were carried out with Dictra. Both the STEM measurements as well as kinetic simulations indicate very low coarsening rates for MX and M23C6 precipitates. Dictra simulations showed a reduced influence of Laves phase and Z-phase formation on coarsening of M23C6.