Abstract
The creep resistance of two high chromium ferritic power plant steels (grades P91 and P92) is shown to be considerably influenced by microstructure changes and microstructure stability during long-term isothermal annealing and/or creep over a range of dislocation (power-law) creep. It is suggested that the change in the dislocation substructure is much more important than the indirect effect caused by particle evolution. By contrast, no significant effect of microstructure stability on creep was found in a regime of viscous creep that is inherent to real service loading conditions of the steels of interest. Finally, no deterioration of the creep properties was found for the steels P91 and P92 under cyclic creep (nonsteady stressing and heating) in a regime of power-law creep.

Key words
9–12%Cr steels, microstructure stability, creep behaviour, nonsteady creep loading

Full text (838 KB)