Revealing the Dynamic Recrystallization Mechanism and Hot Workability of Fe–0.15C–10Mn Medium-Mn Steel through Grain Size Distribution and 3D Processing Maps

Abstract

An in-depth understanding of thermal deformation of medium-Mn steels (MMnSs) is crucial for the forming fabrication of key automotive components. In this work, the Fe–0.15C–10Mn MMnSs are compressed under conditions of 900–1150 °C/0.001–10 s⁻¹. Two-stage models, dynamic recovery (DRV) and dynamic recrystallization (DRX), are constructed and proved to be accurately predictive with a correlation coefficient (R) of 0.997% and average absolute relative error (AARE) of 2.67%. Based on the analysis of microstructure evolution, the discontinuous DRX occured at a specific deformation condition of 900 °C–10 s⁻¹, while the continuous DRX generated at other deformed conditions. The discontinuous DRX grains only distributed along pre-existing grain boundaries, showing a necklace-like grain structure with multiple small zigzag protrusions at the boundary. While continuous DRX grains with low dislocation density distributed both along and inside the pre-existing grain boundaries. The developed 3D processing map identified high strain rate (0.1–10 s⁻¹) as instability domains, in which heterogeneous microstructure are observed. Consequently, optimum hot working domain is determined to be 975–1150 °C/0.001–0.05 s⁻¹. Complete DRX and subsequent growth of small DRXed grains result in a homogeneous microstructure, contributing to the optimal processing zone with η > 0.29.