A new two-dimensional model based on statistical mechanics for describing plastic deformation as well as the resulting microstructural changes is presented. The progress in plastic deformation is described by calculating the dislocation configurations, grain boundary sliding and energy dissipation resulting in entropy maximisation for a two-dimensional FCC crystal structure. The model provides a quantitative tool for determining deformation conditions leading to the occurrence of solid - solid microstructural changes such as subgrain nucleation, recovery and recrystallization. The impact of grain size is analysed by highlighting the behaviour of ultra fine grain and nano-grained materials. The model is applied to FCC Fe (austenite) showing good agreement with experimental observations
