Effect of microstructure on strain-hardening behaviour of a Ti-IF steel grade

Abstract

Thermomechanical processing parameters were adjusted during the processing of Ti-IF steel sheet to obtain microstructures with different grain sizes and precipitation states. The grain size and precipitation state were fully characterized for each specimen in order to investigate the effect of each on mechanical properties. Uniaxial tensile tests were performed at a strain rate of 2·10-3s-1 at room temperature. Relationships between strain-hardening coefficient, n, and mechanical properties were analysed. Differences in measured n-values between the different specimens are associated to a change in yield strength resulting from hardening effects of precipitates and grain size at the beginning of plastic deformation. The role of grain size and precipitation state on strain-hardening behaviour is discussed in terms of their effect on dislocation structure evolution. A strain transition exists where dislocation tangles evolve towards well-defined dislocation cells. It is shown in the present study that the entangled dislocation density is very sensitive to the microstructure for the Ti-IF steel studied while the dislocation cell size appears to be insensitive to the microstructure. © 2005 ISIJ.