Abstract: Effect of solution temperature on microstructure, mechanical properties and fracture morphology of the Fe-Mn-Al-C lightweight austenitic steel was studied by means of optical microscope, scanning electron microscope, spectrometer, tensile testing machine, and impact testing machine. The results show that the tested steel exhibits a density of 6.92 g·cm^-3, corresponding to a density reduction of approximately 11.95% compared to pure iron. Optimal mechanical properties achieve after solution treatment at 1000 ℃ for 1 h, with product of strength and elongation of 37.80 GPa·%, yield strength of 586 MPa, tensile strength of 864 MPa, elongation of 43.7%, and impact absorbed energy of 110.3 J at -20 ℃. Between 900-1050 ℃, as the solution treatment temperature increases, the intergranular κ^*-carbides gradually dissolve, while there are still a large number of small granular κ′-carbides inside the austenite grains that can hinder dislocation movement, and the grain size gradually increases. While, when the solution treatment temperature exceeds 1000 ℃, the phenomenon of abnormal grain growth leads to significant deterioration of the mechanical properties of the material. With the increase of solution temperature, the density of dimples on the impact fracture increases, and the size and depth show a clear growth trend. At the same time, the tearing edge also increases significantly. This microscopic feature is well matched with the improvement of macroscopic mechanical properties.

Key words: solution treatment, high manganese austenitic steel, low density steel, microstructure, mechanical properties