Characterization of reversible permeability in advanced USC steel during thermal aging

The effects of microstructure on reversible permeability (mu(rev)) are discussed for thermally aged ultra superentical (USC) steel, which is required for the next generation of power plants. Thermal aging was observed to coarsen the tempered carbide (Cr23C6) generate the Laves (Fe2W) phase and decrease the dislocation density. The peak position of the mu(rev) decreased drastically during the initial 1000 h aging period, and was thereafter observed to decrease only slightly. The variation in peak position of mu(rev) is closely related to the decrease in the number of pinning sites, such as dislocations, fine precipitates, and the martensite lath.