Abstract
It is well known that tungsten (W) is the key element for creep strength of the advanced martensitic heat resistant steels developed for main steam pipe in ultra-super critical power plant. W is found to suppress coarsening of M23C6 type carbide during creep at elevated temperatures, which can never be predicted according to the conventional Ostwald ripening model for a Fe-X-C system in αFe. In this study, therefore, the effect of W on the coarsening of M23C6 during aging has been analyzed in a detailed experiment and modeled using a modified Ostwald ripening equation for Fe-X1-X2-C system. It is found that W substitutes only for Cr in M23C6 lattice to form [Fe4(Cr, W)19]C6. Using the modified Ostwald ripening equation the coarsening of M23C6 is found to be controlled by the lattice-diffusion of W, resulting in the coarsening rate reduced about one order of magnitude by 1% W addition.
