A set of unified constitutive equations for modelling microstructure evolution in hot deformation

Recrystallisation and recovery are two competing processes. Metals showing high degrees of dynamic recovery are unlikely to recrystallise dynamically, since it is difficult to accumulate the dislocation density to a certain level to initiate recrystallisation. Recrystallisation and recovery may continue after hot deformation, such as during passes in multipass hot rolling processes. Both processes reduce dislocation density of materials and allow large plastic deformation to be achieved. The main aim of this research is to develop a set of mechanism-based unified viscoplastic constitutive equations, which models the evolution of dislocation density, recrystallisation and grain size during and after hot plastic deformation. Deformation mechanisms of metals at high temperatures and techniques of modelling the physical effects are analysed. The effects of dislocation density and recrystallisation on viscoplastic flow and grain size evolution of a micro-alloyed steel are rationalised. Optimisation techniques and procedures are developed to determine the unified viscoplastic constitutive equations from experimental data.