Formation of an Ultrafine-Grained Austenite-Containing Microstructure from a Cold-Rolled Medium-Manganese Steel Processed Using Intercritical Annealing

The behavior of 60% cold-rolled medium-manganese steel (0.1C5Mn) during intercritical annealing, has been examined using various techniques. Microstructural observations showed a slight coarsening of the subgrain/grain structure during intercritical annealing, without any apparent change in the misorientation distribution. In addition, the formation of ultrafine austenite grains took place mainly at high-angle boundaries and rarely at low angle boundaries, suggesting a heterogeneous austenite nucleation process in this steel. The results indicated that the annealing behavior of cold rolled medium manganese steels is controlled by the extensive recovery of the ferrite phase and formation of austenite phase with an austenite volume fraction of ~20%. It was proposed that the segregation of manganese and carbon to high-angle boundaries promoted austenite nucleation and growth, as such segregation decreases the Gibbs energy of austenite.