Effect of a two-phase region annealing process on microstructure and mechanical properties of medium manganese steel

In order to develop third-generation automobile steel with perfect tensile strength and elongation, cold-rolled medium manganese steel was annealed in a two-phase region using a high-temperature tube atmosphere annealing furnace. The microstructure evolution and mechanical properties of 0.13% C-5.4% Mn low-carbon cold-rolled medium manganese steel in different annealing temperatures as well as different annealing times were investigated by means of scanning electron microscopy, transmission electron microscope and X-Ray Diffraction. The results indicated that the main microstructure after annealing was ultra-fine grained ferrite, austenite and martensite. Annealing temperature of the two-phase region was between 625 degrees C and 700 degrees C; the highest content of austenite was 20.23% at 675 degrees C. The annealed time increased from 10 min to 2 h. With the extension of annealing time, the austenite volume fraction decreased first and then increased, which was 20.20% and 20.23% at 10 min and 2 h, respectively. The optimum comprehensive mechanical properties were obtained at 675 degrees C for 2 h. The tensile strength was 900 MPa, the elongation was 25%, and the tensile strength and elongation reached 22.4 GPa%.