Development of Ultrafine Lamellar Ferrite and Austenite Duplex Structure in 0.2C5Mn Steel during ART-annealing

The microstructural evolution of Fe-0.2C-5Mn steel during intercritical annealing with holding time for up to 144 hours was examined by TEM and STEM. It was demonstrated by TEM that the martensite lath structure gradually transformed into a lamellar ferrite and austenite duplex structure. The partitioning of manganese from ferrite to austenite was found by STEM. Typical Kurdjumov-Sachs orientation relationship between austenite lath and ferrite lath was observed by electron back scattered diffraction (EBSD). Based on the analysis of the austenite lath thckening behavior, it was proposed that the Mn-partitioning in austenite dominated the microstructure evolution of the ultrafine lamellar ferrite and austenite duplex structure during annealing process.