Modelling of dynamic and metadynamic recrystallisation during bar rolling of a medium carbon spring steel

A constitutive model for hot deformation of a medium-carbon spring steel has been developed and validated using isothermal compression experiments at monotonic and abruptly changed strain rate conditions, providing data for the flow stress and softening kinetics. The integrated deformation-softening constitutive model is based on the two hypotheses: (a) instantaneous response of the microstructure to varying temperature-strain rate conditions and (b) invariance of the kinetics of different strain states having equal effective plastic strain. It has been implemented in a FEM code and applied to bar and rod hot rolling schedules. The predictions for the plain medium-carbon steel considered indicate that dynamic (DRX) and metadynamic (MDRX) recrystallisation are possible to occur in both the roughing and finishing mills. A comparison for the same rolling schedule applied to a medium-carbon multialloyed steel shows that its higher resistance to DRX cannot prevent recrystallisation in the intermediate mill, but it can in the finishing mill if there is no significant strain accumulation.