Grain boundary diffusion controlled ultrafine grain formation during large strain-high Z deformation of coarse (200 μm) grained ultra-low carbon steel

In the present study, development of microstructure and grain boundary characteristics during large strain-high Z (Zener–Hollomon parameter) deformation of a coarse (200 μm) grained ultra-low carbon steel in the ferrite region was carried out. The grain size (d)–Z parameter relationship: d = 300Z−0.16 was established for this material. Based on the correlation between the measured grain sizes and calculated characteristic diffusion distances for various testing conditions, diffusion along grain boundaries was found to be the mechanism controlling ferrite grain size in this material processed through large strain-high Z deformation.