Abstract
This paper investigates the effects of intercritical annealing time on the mechanical properties, microstructure, and element distribution of Fe-0.21C-10Mn-4.8Al-0.5Cu-0.4Cr-0.2Ti medium manganese steel by setting different intercritical annealing times in the critical zone. The mechanisms of the observed phenomena were analyzed using characterization methods such as tensile testing, hardness testing, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The results show that the material exhibits a tensile strength of 1250 MPa, an elongation of 45 %, and a strength-ductility product as high as 56.3 GPa%. The optimal microstructure is observed to be a complex phase structure primarily composed of austenite with multiple morphologies, δ-ferrite, and martensite. With the prolongation of annealing time, the morphology of retained austenite gradually transforms from fine lath-shaped to larger block-shaped austenite. The thermodynamic stability and mechanical stability of retained austenite in the AT40 sample are significantly optimized, thereby enhancing the mechanical properties of the sample.

Key words
intercritical annealing, complex phase, stability of retained austenite

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