Thermodynamic study of the critical nucleus size for metadynamic recrystallisation

On the basis of thermodynamics, it is shown that the critical nucleus size for metadynamic recrystallisation is smaller than that for dynamic recrystallisation. It follows that the nucleation rate of metadynamic recrystallisation is not zero. A Cr25Ti steel was hot deformed and its recrystallised structures were examined after delayed quench. It was observed that after the deformation was terminated, both the grain size and the subgrain size decreased at first, although the grains eventually coarsened at longer times. This is attributed to the conversion of potential embryos formed during dynamic recrystallisation into true nuclei in metadynamic recrystallisation. The results from the experiment appear to be consistent with the theoretical analysis.