Synergistic Enhancement of Strength and Ductility in Fe‐20Mn‐9Al‐1.2C‐2Ni Lightweight Steel via Intergranular Precipitate Dissolution and Grain Boundary Engineering

Hot‐rolled Fe‐20Mn‐9Al‐1.2C‐2Ni (wt%) lightweight steel undergoes solid solution treatment to enhance strength and ductility. The microstructural evolution and mechanical properties of the steels are analyzed at various solution treatment temperatures ranging from 900 to 1050 °C. As the solid temperature increases, the intergranular precipitates (elongated coarse κ*‐carbides) gradually dissolve, and the proportion of “special boundaries” increases. This process allows strengthening elements to migrate into the austenite matrix, and refining the effective grain size. These coupling effects lead to a synergistic enhancement of strength and ductility. The sample S1000, treated at 1000 °C, demonstrates a remarkable mechanical performance with a yield strength of 937 MPa, an ultimate tensile strength of 1065 MPa, and a total elongation of 65.3%. This sample also shows a high special boundary fraction of 54.7%, and a fine effective grain size of 3.16 μm, accompanied by a uniform distribution of strengthening elements (C, Mn, and Ni) within the austenitic matrix. However, when the solid solution temperature increases to 1050 °C, rapid grain growth occurs, leading to a deterioration in the tensile properties. Calculation results indicate that the enhancing mechanisms include solid solution strengthening, fine‐grain strengthening, and dislocation strengthening.