Ferritic and Martensitic Steels for Power Plants

The metallurgical background and the physical properties of the steels used in power plant are briefly described. The microstructures of the steels after the production heat treatment and after long-term service exposure are discussed and the mechanical properties, especially the creep rupture strength, are shown. The strengthening mechanisms are considered and effects of the microstructural changes after long-term service exposure on the creep rupture strength explained. Because of the microstructural changes, care has to be taken in deriving long-term creep rupture strength estimates from experimental data. It is shown that steam oxidation may be a significant life-limiting factor for thin section components operating at temperatures around 600 o C.