Novel Post-Weld Heat Treatment for Reduced Activation Ferritic/Martensitic Steel Electron Beam Welds

Structural components in a fusion reactor must withstand the diverse range of demands placed on the component by fusion reactor conditions, including 14 MeV neutron irradiation, He exposure and temperatures possibly up to 650°C. Joints between structural materials maintain integrity during operations, but residual stresses that are left after welding can cause them to fail unpredictably. There are several candidate materials that are being considered for the UK Atomic Atomic Energy Authority ‘STEP’ (Spherical Tokamak for Energy Production) reactor. In line with the NEURONE (NEUtron iRradiatiOn of advaNced stEels) programme, this project will analyse Eurofer97 electron-beam welds in order to determine the effectiveness of novel heat treatments and the response of the joints to irradiation. To achieve this, novel heat treatments will be carried out ex-situ and in-situ for neutron diffraction experiments to assess residual stresses, microstructure and internal defects. The contour method, a lab-based technique will also be used to measure residual stresses and additionally electron microscopy will be used to analyse the microstructure around the weld. Following this characterization, ion irradiation experiments will be carried out at UoM on the welds to determine response to reactor conditions. This is crucial to determine optimum heat treatments and to understand the performance of the joints in service.