INFLUENCE OF THE MICROSTRUCTURE ON STRAIN-HARDENING OF STEELS

Steels with defined varied microstructural parameters were investigated at high deformations with a phenomenological model of Kocks. It was found that the entire deformation of the steels has to be separated into deformation stages III and IV. Strain hardening is influenced by the microstructure: Like yield stress the strain hardening rate of steels is increased by precipitates and hard secondary phases. Both affect the dislocation free path but not the dynamic recovery. The stress-strain curves can be described physically and precisely by the Voce equation which can be derived from the Kocks model. The Hollomon equation and the n value, which is widely used in technical applications, are not suitable for the description of strain hardening. The average strain hardening of steels can be conveniently described by a new parameter, V. For the extrapolation of stress-strain curves to large strains the existence of deformation stages III and IV has to be taken into account because otherwise large errors occur. A new method for the extrapolation of stress-strain curves is proposed.