Microstructure evolution of the cast martensitic steel G-X12CrMoWVNbN 10-1-1 during creep at 823 K

Microstructure of the cast martensitic steel G-X12CrMoWVNbN 10-1-1 after creep for 12 434 h to fracture at 823 K was quantitatively investigated by electron microscopy. EDS has been used to discriminate type of precipitates. The size distributions of subgrains and precipitates of the types M23C6, VX, NbX (M: metal, X: C, N) and Laves phase were determined from electron microscopy images. The volume fraction of these precipitates was calculated. Subgrain microstructures develop as a function of creep strain. No coarsening takes place for M23C6 and MX after creep. Laves phase additionally precipitates during creep and thereby leads to significant increase of volume fraction. The stability of precipitates and their relation to creep properties are discussed.