The effect of particle morphology and grain refinement to the nanometer scale on strength, work-hardening and tensile ductility of reduced activation ODS-(7–13)Cr steels has been modelled with a dependence on deformation temperature ( T=RT–700 °C) and a superimposed irradiation hardening. The Orowan model predictions describe as the upper limit the observed particle strengthening of various ODS-(7–13)Cr-(⩽0.5 wt% yttria) steels. An optimum particle size d p ∗≅7–22 nm ( f v=0.004–0.05) and strength, together with a lower limiting ultra-fine grain size d K,c⩾90 nm result in maximum uniform ductility increase by grain refinement and dispersion hardening (DIGD). Optimum size d p ∗ increases with increasing particle volume fraction f v and deformation temperature and decreases with irradiation hardening and grain refinement. The region of DIGD is limited to achieve a critical strength σ L corresponding to a critical particle volume fraction f v,c and grain size d K,c, above which uniform strain becomes limited by the strong drop of fracture strain. Grain refinement and irradiation hardening decrease σ L, f v,c and increase d K,c. In accordance with experimental results of ODS-Eurofer, nominal uniform strain increases with increasing f v by about ε u,n= B e+ A eln f v, most strongly around 300 °C, but weakly at the 600 °C minimum. The strong ductility increase above 600 °C results from a reduction of dislocation annihilation and structural recovery of strength. At T<300 °C, grain refinement increases uniform ductility up to d K,c for lower f v toward a saturation value which increases with increasing ratio of shear modulus to Hall–Petch constant. The enhanced uniform ductility at T⩾300 °C is otherwise strongly decreased by grain refinement, more pronounced at lower f v and for strengths above σ L.