The evolution of precipitates of 22Cr-25Ni-Mo-Nb-N heat-resistant austenitic steel in long-term creep

The microstructural evolution of 22Cr-25Ni-Mo-Nb-N heat-resistant steel after creep under different stresses at 973 K has been systematically investigated. It is found that during short time creep MX and M23C6 predominantly precipitate in the matrix. While with the increase in creep time, Cr3Ni2SiX and σ precipitate in the matrix. MX is the main strengthen precipitate in the matrix after long time creep. Due to a fast coarsening rate, M23C6 in the matrix has a little effect on strengthening the matrix. Comparing the MX and M23C6 in the crept sample with those in the aged sample, it could be found that the creep stress can promote the coarsening rate of MX and has hardly any effect on the coarsening of M23C6. The effect of stress on the coarsening of precipitates focuses on the diffusion of solution atoms. Under the condition of stress, the diffusion of Nb is accelerated, while that of C changes little.