Abstract
Grain size dependence of creep rupture strength and creep strain rate was experimentally decided for tungsten containing 11% chromium ferritic steels at elevated temperatures. A different forging ratio for the same cast ingot following the same heat treatment extracted the grain size effect of temepered martensitic microstructure on a creep deformation rate and a microstructure evolution during the creep. Fine block grain increased the nucleation site of intergranular ferrite during the creep which was observed through Transmission Electron Microscope for thin foils prepared from ruptured specimens. Grain boundary microstructure recovery was explained by modified “core-mantle-model”, proposed by Terada et al., assuming the mantle width increase during the creep deformation in ferritic microstructure equivalent to a grain boundary slip or a grain boundary diffusion mechanism for austenitic microstructure.
