Postirradiation tensile behavior of nickel-doped ferritic steels

Tensile specimens of normalized-and-tempered 9Cr-1MoVNb, 9Cr-1MoVNb-2Ni, 12Cr-1MoVW, 12Cr-1MoVW-1Ni, and 12Cr-1MoVW-2Ni steels were irradiated in the High-Flux Isotope Reactor (HFIR) at 300, 400, and 500°C to displacement-damage levels of up to ˜11 dpa. The nickel was added to the ferritic steels to produce helium by a two-step (n, ) reaction during irradiation in this mixed-spectrum reactor. Up to 103 appm He was produced in the steels with 2% Ni. Irradiation at 300 and 400°C caused an increase in strength of all the steels relative to the strength in both the normalized-and-tempered condition and after aging the normalized-and-tempered steel for a time period similar to that in the reactor. The strength increases were accompanied by a loss of ductility. At 500°C, there was little change in the strength properties of the steels. The results at 300 and 400°C indicate an effect of helium on the strength increases; no helium effect was apparent for the specimens irradiated at 500°C.