The influence of helium on the high temperature mechanical properties of an austenitic stainless steel

Foil specimens of DIN 1.4970 austenitic stainless steel were cyclotron implanted to uniform helium concentrations up to 150 ppm. Subsequently, tensile and creep tests at different stress levels and temperatures between 600 and 8000C were performed and compared with the results from He-free control specimens. Whereas the latter exhibit transgranular ductile fracture, the implanted material breaks by intergranular failure with a corresponding reduction of the elongation to fracture values by factors between 3 and 6. These results and the TEM and SEM investigations of the microstructure are discussed by means of an embrittlement model which is based on the stress assisted nucleation and growth of helium filled grain boundary cavities. (Auth.)