Numerical Approach to Evaluate Cold Crack Susceptibility in Laser Beam Welds of Reduced Activation Ferritic/martensitic Steel F82H to Construct Blanket Modules

Fusion reactor is expected as one of the next generation electric energy sources to realize the suppression of global warming, due to reduction of carbon dioxide during its operation for power generation. The blanket modules will be set on the inner wall of fusion reactors to transfer the neutron kinetic energy to thermal energy for steam turbines operating and to confine neutron in the reactors. The reduced activation ferritic/martensitic steel F82H has been developed to construct the blanket modules by modification from 9%Cr heat resisting steels. In the case of laser beam welding (LBW) for the steel, martensite is usually formed in welds during welding processes. As well known, cold cracking should be concerned in welds of high strength steels hardened by martensite. Therefore, cold crack susceptibility was evaluated by hydrogen concentration and residual stress calculated by the newly developed numerical analysis method as compared with the measured criteria by a slow strain rate tensile (SSRT) test in this study. The SSRT test was performed for the specimens with hydrogen charged by electrochemically and coated by zinc to trap hydrogen inside. By comparing the calculated hydrogen contents and stress with the obtained criteria, it was judged that cold cracking does not occur in the weld of F82H. Actually, the experimental verification could not recognize cold cracking in the welds of F82H. These results suggest that the cold crack susceptibility is sufficiently low and the cracking can be prevented in the welds.