In this work an atomistic multi-scale modelling approach is applied to study: (i) the kinetics of phase separation during thermal ageing of binary Fe–Cr alloys and (ii) the interaction of dislocations with Cr-rich precipitates. The studies were performed varying the Cr content in the range of 12–18 at.% Cr and at temperatures from 600 to 900 K, which is within the miscibility gap where phase separation occurs. Thermal ageing was simulated using atomistic kinetic Monte Carlo techniques while the interaction of a dislocation with Cr-rich precipitates was studied by molecular dynamics. In both cases the description of atomic interactions was provided by the same semi-empirical interatomic potential, partially fitted to available ab initio data. Both studies are combined to analyse the hardening of Fe–Cr alloys during thermal ageing.