The transition from multiple- to single-peak recrystallization during the hot working of austenite

Abstract

For the three free-machining steels and a low alloy steel tested, the high temperature stress-strain curves obtained in torsion testing in the approximate range 850–1150°C and at a constant strain rate in the approximate range 10 −3−5 s −1 are characteristic of the occurrence of dynamic recrystallization. In both types of steel, there is a change in the shape of the stress-strain curves from a form with a distinct peak followed by regular oscillations to a form with a single peak when a critical value of the Zener-Hollomon parameter (characteristic of the material) is exceeded. The criteria proposed to predict the transition from regular oscillations in flow stress to a single peak have been shown to be equivalent for a constant ratio (adjusted to transition experimental data) of the critical strain for the onset of recrystallization to the strain to the first peak in flow stress. It is now shown that a common strain ratio for the transition of both types of material (independent of the initial grain size and hot-working conditions) is derived from an available dynamic recrystallization model and that this strain ratio again yields the equivalence of the “critical strain condition” and the “relative grain size model”.