HELIUM EMBRITTLEMENT OF TI AND P ADDED AUSTENITIC ALLOYS CREPT AT 923K

The helium embrittlement response of Ti and P modified and thermomecha nically treated Fe-25% Ni-15% Cr type austenitic alloys was studied th rough post helium implantation creep testing. Helium was introduced in to the specimen at 923 K with a concentration of about 60 appm by heli um-3 ion irradiation with a cyclotron. Subsequent creep tests were car ried out at the same temperature. In terms of creep rupture time, no s ignificant degradation by helium was appreciated in the Ti added alloy , although the P modified one suffered from about a 40% reduction. On the other hand, a helium-related decrease in the rupture elongation wa s perceived in both alloys to a considerable extent. The beneficial re sult obtained from the Ti modified alloy suggests that the mechanical property deterioration induced by helium could be suppressed by proper Ti addition and/or microstructure controlling even in alloys with int ermediate nickel contents (20-25%), like in Type 316 stainless steels of less nickel content. (C) 1998 Elsevier Science S.A. All rights rese rved.