RADIATION-INDUCED SEGREGATION AND HIGH-TEMPERATURE DUCTILITY IN 12-PERCENT CRMOVNB FERRITIC-MARTENSITIC STEEL

The influence of neutron irradiation at 650-degrees-C to a displacement dose of 0.2 dpa on the elevated temperature tensile ductility of a 12% CrMoVNb ferritic-martensitic steel has been investigated. Irradiation induces increases in elongation to fracture by more than a factor of two in 600-degrees-C tests. These trends can be semi-quantitatively correlated with microvoid formation at carbides and with the presence of matrix helium bubbles in the irradiated steel, which are postulated to act as additional microvoid initiators. The latter modify the ductile dimple fracture process and account for the enhanced post-irradiation ductility. Radiation-induced solute segregation to internal sinks has been modelled. The calculations suggest that segregation to martensite lath and prior austenite grain boundaries is minimal for the irradiation conditions used, and therefore does not contribute measurably to the observed ductility changes.