Role of carbon content in governing strengthening mechanisms and deformation behavior of Fe–Mn–Al–C lightweight steels

This study investigated three low-density steels—Fe–28Mn–6Al–0.2C, Fe–30Mn–8Al–0.6C, and Fe–30Mn–8Al–0.8C—by characterizing microstructural evolution during solution treatment via optical microscopy (OM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). By integrating hardness, tensile, and Charpy impact test results, we elucidated the interdependence between mechanical properties and microstructures, and further examined the evolutionary characteristics of textures induced by tensile deformation. After solution treatment at 1000 °C, the Fe–28Mn–6Al–0.2C steel retains a strong Cube texture, which mainly inherits from the dendritic structure of as-cast microstructure. After tensile deformation, the texture evolves into Copper and S textures. The evolution of texture components in the Fe–30Mn–8Al–0.6C and Fe–30Mn–8Al–0.8C steels during tensile deformation—manifested as progressively weakened Copper texture and enhanced Brass texture—is attributed to planar dislocation slip. By comparing the deviation between predicted and measured yield strength values, this study identified a theoretical calculation model suitable for predicting the yield strength of non-deformed Fe–Mn–Al–C steel. With increasing solution temperature, the impact toughness of Fe–30Mn–8Al–0.6C showed a trend of initial increase followed by a slight decrease, while that of Fe–30Mn–8Al–0.8C steadily improved. This divergence is attributed to differences in carbon content, grain boundary character, and grain size evolution between the two steels.