Creep resistant ferritic steels for power plants

The development of power plant technology towards larger units and higher efficiencies is linked to the development of creep resistant ferritic steels. Starting with simple CMn- steels, creep strength has improved successively by introducing new alloying elements and new microstructures. Niobium has been one of the most successful new elements. It is contained in all the latest high strength steels belonging to the group of 9-12%Cr- steels. The use of these steels allows the design of power plants with steam temperatures up to 625degreesC. As a further step ferritic steels are currently under development for maximum steam temperatures of 650degreesC, which is believed to be the limit that can be achieved for this group of steels.