A cost-effective strain-aging 2300 MPa grade medium-Mn steel (Fe-0.34C-7.4Mn-1Si-0.2V, mass fraction, %) was melted and cast. The steel was subjected to 4% pre-strain before hot rolling, then tempering at 200 ^oC for 20 min, 1 h, and 2 h respectively, after being hot-rolled. There after the evolution of volume fraction, grain size, dislocation density, and bake hardening (BH) effect of the austenite was systematically analyzed, in terms of the effect of pre-strain and annealing time on microstructure and properties of the steel. Key findings include: after pre-straining, the austenite volume fraction decreased from 31% to ~8%. Prolonged tempering coarsened austenite grains from 0.4 μm to 1 μm, while the yield strength increased from 2198 MPa to 2311 MPa, with uniform elongation stabilized at 9.1%-10.3%. A remarkable bake hardening effect was observed, with BH values rising from 460 MPa (20 min) to 573 MPa (2 h), primarily due to Cottrell atmosphere formation via carbon diffusion, which pinned dislocations. The enhanced yield strength was dominated by dislocation strengthening (pre-strain-induced) and bake hardening effect, synergistically ensuring stable performance across a wide tempering window (20 min-2 h). The low sensitivity to tempering time and broad process tolerance highlight this steel's suitability for large-scale industrial production.