A New Approach to Modeling the Flow Curve of Hot Deformed Austenite

Abstract

A new, more physically realistic and practically useful model is presented for the simulation of high temperature austenite flow curves. It is an extension of our earlier empirical model based on the Avrami kinetics of dynamic recrystallization. In the new approach, the normalization parameter is expressed in terms of the fractional recrystallization and not the amount of softening. Compression experiments carried out on a Nb-modified plain carbon steel enable the simulated flow curves and progress of recrystallization predicted by the two models to be compared.

Simulation of Austenite Flow Curves under Industrial Rolling Conditions Using a Physical Dynamic Recrystallization Model

“…(1). 15) This rule of mixtures is based on the current values of the work hardening flow stress σwh pertaining to the unrecrystallized material and the dynamic recrystallization flow stress , which represents the average flow stress of the material that has already undergone dynamic recrystallization. Here X is the fractional softening due to DRX, which can be defined as X=(σwh -σ)/(σwh -).…”

“…In this relation, the saturation stress σsat in Eq. (3) is replaced by the critical stress σc, the stress value for the initiation of DRX, which has previously been demonstrated to be equal to the steady state stress σss; 15) it can be considered as the average stress when all the grains have undergone at least one cycle of DRX. The work hardening parameter r', is introduced to take into account the average recovery rate of the crystals that are currently at different stages of DRX in the recrystallized portion of the material.…”

“…8) was proposed in a recent study 15) based on employing the mean flow stress of the material undergoing DRX together with the work hardening curve pertaining to the grains in which DRX has not yet nucleated. The innovation in this newer method consisted of the simplifying assumption that the flow curve pertaining to the material that has undergone DRX begins at the critical strain for dynamic recrystallization and follows the kinetics of the overall flow curve.…”

“…This method has been shown to model austenite flow curves with acceptable accuracy. 15) In the present study, the improved model is applied to three different grades of steel and used to predict flow curves at the strain rates involved in industrial rolling operations, which are not readily attainable in the laboratory.…”

Dynamic recrystallization behaviour of spheroidal graphite iron. Application to cutting operations

“…Additionally, both the Avrami exponent and the time required to achieve 50% DRX are determined from the work-softening transients present in some of the stress-strain curves. However, the model can be simplified on the ba-M a n u s c r i p t sis of the experimental results reported by Jonas et al (2009) and Quelennec et al (2011), who demonstrated that, for a broad range of steel grades, the steady state stress is equal to the critical stress for the nucleation of DRX.…”