Abstract
The dose dependence of true stresses has been investigated for nuclear structural materials such as A533B pressure vessel steels, modified 9Cr-1Mo and 9Cr-2WVTa ferritic martensitic steels, 316 and 316LN stainless steels, and Zircaloy-4. After irradiation to significant doses, these alloys show radiation-induced strengthening and often experience prompt necking at yield followed by large necking deformation. In the present work, the critical true stresses for deformation and fracture events, such as yield stress (YS), plastic instability stress (PIS), and fracture stress (FS), were obtained from uniaxial tensile test data or calculated using proposed methods. The true fracture stress was nearly independent of dose before embrittlement occurred, as was the plastic instability stress before the critical dose to prompt necking at yield was reached. A few bcc metals such as ferritic martensitic steels experienced significant embrittlement at high doses above ~1 dpa; from which the fracture stress decreased with dose and then the materials fractured before yield at or above 10 dpa. It is anticipated that metallic materials will retain significant fracture toughness after irradiation as long as they show significant necking ductility.
