A phenomenological theory of the irradiation embrittlement of iron and steel

Abstract

The shift of the ductile-brittle transition temperature with neutron irradiation is structure sensitive. In this study, the effect of micro-structure on the transition temperature of iron and steel, before and after irradiation, is analysed and discussed.At first, yield stress (σy) and fracture stress (σf) are given by the Fetch relation, and it is assumed that the effect of interstitial or substitutional solute atoms, dislocations and precipitates are included in the term that is independent of grain size. Secondly, the ductile-brittle transition is given by the temperature at which σy = σf. From the assumptions the effects of structural factors on the ductile-brittle transition temperature, before and after irradiation, are obtained. Before irradiation, the finer the grain size, the higher the transition temperature. The higher the concentration of interstitial atoms, the higher the transition temperature. However, this may not always be so for substitutional alloying elements. If precipitates are closely spaced, the transition temperature is decreased. An increase of dislocation density results in an increase in the transition temperature. With respect to irradiation sensitivity, the analysis shows that the grain size, substitutional or interstitial atoms, precipitates and dislocation densities affect the transition temperature depending on the change of the coefficients for each of the factors with irradiation. Finally, the effect of the structural factors on the transition temperatures after irradiation was analysed. The conclusions from this analysis are compared with experimental results.