Microstructural evolution of the martensitic cast steel GX12CrMoVNbN9‐1 during long‐term annealing and creep

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Abstract
The microstructure of four specimens of the martensitic cast steel GX12CrMoVNbN9‐1 crept to fracture at 873 K for 220‐33027 h was quantified by electron microscopy with regard to large M23C6‐particles, small V‐ and Nb‐containing particles, dislocations, pores, and oxidation layers. The laws of time‐dependent coarsening of particles and strain‐controlled growth of subgrains are consistent with those previously established for X20(22)CrMoV12‐1. Using these data the microstructural model of deformation developed for X20(22)CrMoV12‐1 can explain the creep behaviour of GX12CrMoVNbN9‐1. The minimum in creep rate is related to the coarsening of particles and subgrains. At low stresses (< 140 MPa) the fraction of small slowly coarsening V‐ and Nb‐containing particles leads to improved creep resistance. The material resists against pore formation; fracture occurs by necking.