Specimens fabricated from a split heat of an iron base precipitation hardening alloy (A-286) containing three levels of natural boron were irradiated at reactor ambient temperatures and then tested at a temperature of about 650 C. The boron levels in the three heats were about 0.001, 0.004, and 0.010 weight per cent. Irradiations were performed in the Engineering Test Reactor (ETR) to a fast neutron dose (fluence) of about 4.9 × 10¹⁹ n cm^-2 (E_n > 1 Mev) and a thermal neutron dose (fluence) of about 6.2 × 10²⁰ n cm^-2.

Test results show that the times to rupture were not significantly different for unirradiated specimens fabricated from the three heats, however, those specimens containing the least amount of boron did exhibit slightly lower ductilities.

The data indicate that the stress dependency of the time to rupture has not been affected as a result of the irradiation. In addition, it is shown that the specimens fabricated from the heat containing the higher boron concentration results in essentially no change in the time to rupture values, although there is a large decrease in the elongation and in the reduction of area. Specimens having the lower boron content show factors of about 7 reduction in the time-to-rupture and corresponding decreases in the elongation and the reduction of area. Although the ductility of the irradiated specimens for each heat shows large decreases, the specimens containing the least amount of boron showed the greatest change.

The experimental data tend to indicate that the boron may play a dual role in the creep-rupture properties of irradiated precipitation hardening alloys. It is proposed that the boron concentration may be relatively high along the grain boundaries and other imperfections than that existing within the grains. The combined effect of the localized atom displacements, the possible nucleation of precipitate phases (carbon, nitrides, and borides) and the generation of helium atoms will all tend to embrittle these alloys at elevated temperatures.