Radiation-induced structure-phase transformations in austenitic stainless steels

The effect of electron irradiation with an energy of 1.0 to 2.3 MeV on the structure-phase stability of austenitic chromium-nickel and chromium-manganese stainless steels has been studied. It is shown that following electron irradiation with a displacement rate of about 10-8 dpa/s minor clusters of atoms occur in SS316L and EP838 stainless steels. These clusters may be seen with the help of small-angle X-ray scattering and electron microscopy. Their formation process is subject to thermal activation and is accompanied by growth of the specific electrical resistance. The activation energy of this process has been determined to be 0.30 and 0.33 eV for EP838 and SS316L steels, respectively. Thermal ageing activation energies in these steels are 0.53 and 0.59 eV, respectively. Additional in situ irradiation with high rate electrons in a high voltage electron microscope up to a rate of 0.2 dpa resulted in precipitate coarsening and in partial growth of the above clusters up to a magnitude of 150 to 200 A. The volume density of the clusters following the additional irradiation was approx. 0.2%. (author)