On the swelling resistance of ferritic steel

Abstract

Transmission electron microscopy has been used to study the microstructural features associated with void swelling resistance in FV448 martensitic stainless steel after fast reactor irradiation to damage levels of 30 dpa at temperatures in the range 380-460 °C. A characteristic feature of the microstructures is the presence of domains in which the high pre-irradiation network dislocation density is eliminated, and replaced by a homogeneous population of interstitial dislocation loops with a⟨100⟩ Burgers vectors. These domains grow but remain interspersed within a martensitic-type matrix that still retains high network dislocation densities. It is suggested that the observed evolution of the damage structure and the associated swelling resistance in such b.c.c. materials is due to the relative rates of nucleation and growth of the two interstitial dislocation loop types, with 1/2a⟨111⟩ and a⟨100⟩ Burgers vectors.