Dynamic recrystallization during the transient deformation of a vanadium microalloyed steel

Abstract

The nature of dynamic recrystallization stress-strain curves was studied following an increase or decrease in strain rate after deformation into the steady state region. For this purpose, a vanadium microalloyed steel was hot compressed at constant true strain rates of 5.6 × 10 −5s −1 to 7.4 × 10 −2s −1 at a testing temperature of 1000°C. After an increase in strain rate, the flow curve displayed a single peak; the strain ε p ′ in this case was distinctly smaller than that associated with the annealed structure. After a decrease in strain rate, by contrast, the flow curve displayed a multiple peak; under these conditions ε p′ was nearly equal to that for the annealed structure. The transients observed after a strain rate change were of the inverse type, thus differing sharply from those observed when dynamic recovery is rate controlling. The critical condition at which the shape of the stress-strain curve changed from the multiple to the single peak type was D s1 = D s2 , (Here D s1 and D s2 are the stable dynamically recrystallized grain sizes before and after the change in strain rate, respectively.) This differs from the critical condition for the annealed structure, i.e. D 0 = 2 D s1 where D 0 and D 2, are the initial and stable grain sizes. These results are interpreted in terms of a grain size based model for dynamic recrystallization.