Flow stress behaviour, static recrystallisation and precipitation kinetics in a Nb-microalloyed steel after a strain reversal

In the present work, a Nb microalloyed steel has been hot worked in torsion mode following multipass deformation sequences. Some of these sequences involve a reversion of the strain. The effect of this reversion on the mechanical response of the steel on reloading after the pre-straining has been analysed. For pre-strains within the strain hardening deformation range, after a transient, the normal flow curve shape corresponding to austenite exhibiting a single peak dynamic recrystallisation is reached. However, the new position of the peak indicates that the dynamic recrystallisation is clearly delayed by the reversal. Deformation sequences including holding times after different strain paths have been used to study the effect of the reversal on the static softening and the strain induced Nb(C,N) precipitation. A complex relationship between the kinetics of both processes and the strain path is observed.