On the modified grain-size-distribution method to evaluate the dynamic recrystallisation fraction in AISI 304 stainless steel

Abstract

The purpose of the present work was to verify the grain size distribution (GSD) method, which was recently proposed by one of the present authors as a method for evaluating the fraction of dynamic recrystallisation (DRX) in a microalloyed medium carbon steel. To verify the GSD-method, we have selected a 304 stainless steel as a model system and have measured the evolution of the overall grain size distribution (including both the recrystallised and unrecrystallised grains) during hot compression at 1,000 degrees C in a Gleeble machine; the DRX fraction estimated using the GSD method is compared with the experimentally measured value via EBSD. The results show that the previous GSD method tends to overestimate the DRX fraction due to the utilisation of a plain lognormal distribution function (LDF). To overcome this shortcoming, we propose a modified GSD-method wherein an area-weighted LDF, in place of a plain LDF, is employed to model the evolution of GSD during hot deformation. Direct measurement of the DRX fraction using EBSD confirms that the modified GSD-method provides a reliable method for evaluating the DRX fraction from the experimentally measured GSDs. Reasonable agreement between the DRX fraction and softening fraction suggests that the Kocks-Mecking method utilising the Voce equation can be satisfactorily used to model the work hardening and dynamic recovery behaviour of steels during hot deformation.