Modelling mechanical property recovery of a linepipe steel in annealing process

In this paper a set of mechanism-based unified viscoplastic constitutive equations has been used to model the effect of microstructural evolution on mechanical property recovery in the annealing process of a cold formed linepipe steel. Dislocation density and plasticity-induced damage accumulation during deformation, and recovery and recrystallisation of the deformed material during subsequent annealing have been modelled. The effects of annealing time on microstructural evolution also have been investigated. Tensile tests were performed on the low carbon ferritic linepipe steel before and after annealing at 700 °C with different holding times. The experimental results have been used to characterise the unified constitutive equations, using an Evolutionary Programming (EP)-based optimisation method. Using these equations, the stress–strain relationships for the interrupted constant strain rate tensile tests were predicted and close agreement between the computed and experimental results was obtained, for various annealing times and for the materials with different amounts of pre-deformation.