Ni segregation and thermal stability of reversed austenite in a Fe–Ni alloy processed by QLT heat treatment

High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) were used to investigate Ni segregation and thermal stability of reversed austenite (RA) in a Fe–Ni alloy processed by quench–lamellarize–temper (QLT) heat treatment. The results show that the 77 K impact energy of the alloy increases with RA content increasing. As an austenite-stabilizing element, Ni is found to segregate in RA, though Ni is not evenly distributed within RA. The amount of segregations increases near the boundary (twice as high as the balanced content) and decreases to some extent in the center of the RA regions. Ni concentration in matrix near the boundary is lower than that in matrix far from the boundary because of Ni atom transportation from α to γ near the boundary. RA in this alloy has high heat and mechanical stability but is likely to lose its stability and transform to martensite when a mechanical load is applied at ultralow temperatures (77 K), which induces plasticity.