Ripening behavior of M23C6 carbides in P92 steel during aging at 800 °C

The rapid coarsening of the M23C6 carbides has been held responsible for the creep fracture in 9-12Cr martensitic heat resistant steels. A commercial P92 steel was subjected to thermal aging at a high temperature of 800 °C to investigate the ripening behavior of the M23C6 carbides. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the microstructure evolution, especially the ripening process of the M23C6 carbides. The new concept of the effective mean size, dependent on the critical radius, was introduced to correct the measured mean size and then the Ostwald theory was applied to describe the ripening behavior of the M23C6 carbides. The ripening of the M23C6 carbides was revealed to be grain boundary diffusion controlled.