Abstract: Fe-C-Mn-Ni-X (where X stands for Cr, V, etc.) austenitic alloy steel forgings were solid solution and aging treated. The effects of aging temperature (650, 700, 750 ℃) and aging time (0-25 h) on the microstructure and mechanical properties of the alloy steel were studied. The results show that the microstructure of solid solution treated and aging treated steels were similar. After aging treatment, a large amount of nano-VC phases in co-lattice or semi-co-lattice orientation with the austenite matrix were precipitated in the alloy steel. The solid solution treated alloy steel showed a strong age hardening capability, the aging time to reach the peak hardness was shorted with increasing aging temperature, and the peak hardness decreased. After aging treatment, the yield strength and tensile strength of the alloy steel increased significantly, the elongation and work hardening index decreased, and the tensile failure mode changed from ductile fracture to ductile-brittle mixed fracture. With the aging temperature increasing and the aging time extending, the strength of the alloy steel was reduced, but the work hardening ability was enhanced.