Effect of Mn-Enriched Cementite on Austenite Formation During Intercritical Annealing

Intercritical annealing (IA) heat treatments are implemented to a variety of steels with the general intent to form austenite and generate composite final microstructures. The austenite may or may not be retained upon cooling from IA. The processing of continuous annealed dual-phase (DP) steels, for example, is intended to generate ferrite-martensite microstructures as the intercritical austenite transforms upon cooling. More recently, IA heat treatments have been extensively studied in application to medium-manganese (Mn) steels, where the general intent is to form intercritical austenite that is retained upon cooling. The stabilization of austenite in Medium-Mn steels is predominantly facilitated by the greater Mn content (4-10 wt pct), relative to DP steels (1.5-2.0 wt pct), which partitions to intercritical austenite, along with carbon (C), during IA and enables the austenite to be retained as a meta-stable phase. During deformation of medium-Mn steels, the meta-stable austenite may exhibit deformation induced martensite transformation, often referred to as transformation-induced plasticity (TRIP)