Influence of accumulated stress in austenite on transformed ferrite grain size by hot rolling for a V-microalloyed steel

Abstract

Torsion test rolling simulations have been performed in different conditions (pass strain, interpass time) for a V-microalloyed steel (C = 0.165; V=0.170wt%). The accumulated stress (Δσ) in austenite at temperatures below the no-recrystallisation temperature (Tnr) has been measured. The accumulated stress is directly related to the dislocation density. The ferrite grain size (Dα) obtained after hot rolling simulations for different conditions and a cooling rate of 3.5 K/s has been measured. Dα is found to be dependent on Δσ and on the austenite grain size prior to the austenite-ferrite transformation during cooling. On the other hand, a higher strain accelerates recrystallisation between passes, lowers the Tnr, value, and consequently leads to a smaller accumulated stress. It is seen that a minimum value of 15 MPa must be reached in order for Dα refinement to begin. © 2008 ISIJ.