Abstract

A 12%Cr martensitic/ferritic with tailor-made microstructure was characterized by HRTEM after tempering (780ºC/2h) and isothermal aging at 650ºC during 2 months and 1 year. The investigation was focused on the precipitation behavior of Laves phase nanoparticles and its contribution to creep response at 650ºC. Although, dense precipitation of Laves phase occurs during the heat treatment (196 nm), addition of 3.8% tungsten (W) promotes a high growth rate of this particle at 650ºC. The excessive addition of W induces a high driving force for the growth of this particle reaching a mean size of 300 nm at 2 months and 400 nm at 1 year. However, some small Laves phase nanoparticles inside the grain were detected at 1 year of isothermal aging, suggesting a low coarsening rate maybe due to low diffusion of W in the matrix. Results of creep test at 650ºC suggest most of the precipitation hardening is granted by fine dispersion of Ta-rich carbonitrides (Ta-MX), i.e. Laves phase is too coarse to contribute to the pinning force of the subgrain structure in the designed alloy.