Microstructure Evolution of a Medium Manganese Steel During Thermomechanical Processing

An as-cast Fe-0.2C-10Mn-3Si-3Al medium manganese steel with a ferrite plus austenite duplex microstructure was subjected to hot compression tests at deformation temperatures within two-phase (alpha + gamma) range and various strain rates. The microstructure evolution of the experimental steel during hot deformation was investigated. The flow curves were characterized by a discontinuous yielding at the beginning of plastic deformation, followed by a weak work hardening to a peak and a subsequent mild softening stage. Two restoration processes took place during hot deformation, namely dynamic recrystallization (DRX) of austenite and continuous dynamic recrystallization of ferrite. The DRX of austenite was believed to dominate the softening stage of the flow curves. The discontinuous yielding stemmed from the existing Kurdjumov-Sachs (K-S) orientation relationship between ferrite and austenite in the initial undeformed microstructure, which gradually weakened during subsequent deformation.