Atom probe tomography and numerical study of austenite stabilization in a low carbon low alloy steel processed by two-step intercritical heat treatment

Film-like retained austenite with a volume fraction of ~10% was obtained in a Fe-0.08C-0.5Si-2.4Mn-0.5Ni (wt%) steel via a two-step intercritical treatment. The retained austenite exhibited ultra-high stability even on cooling to −100°C. Atom probe tomography indicated notable enrichment of C (0.43wt%) and Mn (6.6wt%) in retained austenite. The ultra-high stability of austenite in low carbon low alloy steel is attributed to the combination of partitioning of C and Mn to austenite and the size effect of ultrafine austenite based on thermodynamic analysis. It is underscored that controlled growth of reverted austenite is important for austenite stabilization.