Plastic deformation of structural steels under hot-working conditions

The present study has been conducted in order to formulate a rational description of the flow stress of structural steels, when these are deformed in tension under hot-working conditions. The simplified formulation that has been developed only involves the analysis of the positive work-hardening region of the stress–strain curve and is based on the concepts behind the Mechanical Threshold Stress Model. Accordingly, it is assumed that the flow stress of the material arises from three different contributions: athermal hardening and solid solution, which do not evolve in the course of plastic deformation and work-hardening, the only evolutive component of the flow stress. The evolution of work-hardening is introduced in the formulation by means of the phenomenological work-hardening law earlier proposed by Sah and co-workers, expressed in differential form. The temperature and strain rate dependence of the contributions of solid solution hardening to the flow stress, as well as that of the saturation stress, within the work-hardening law, are described by means of the kinetic model earlier advanced by Kocks. The formulations derived are able to reproduce satisfactorily both the flow stress and work-hardening rate of the material employing a relatively small number of material parameters and therefore, these could be a valuable tool for the analysis of hot-working processes.