Helium induced weldability degradation in an austenitic stainless steel

Autogenous gas tungsten arc (GTA) welding was performed on He-doped type 316 stainless steel. Helium was uniformly implanted in the material using the ''tritium trick'' to levels of 27 and 105 appM. Catastrophic brittle failure occurred in both fusion and heat-affected zones upon cooling of the weld. Microstructural observations of the fusion zone indicate that the pore size, degree of porosity and tendency to form cracks increases with increasing helium concentration. Scanning electron micrographs conclusively show that the weld failure of He-doped materials is due to the precipitation of helium bubbles on grain boundaries and dendrite interfaces. Results of the present study demonstrate that the use of conventional welding techniques to repair or refurbish materials degraded by exposure to irradiation environments may not be feasible if the irradiation results in the generation of even relatively small amounts of helium. 25 refs., 8 figs., 1 tab