Abstract:

Medium manganese steels is a typical of the 3rd generation of automotive steel. The effective control of metastable austenites is one of the key techniques to obtain excellent performances during the austenite reverted transformation (ART) annealing process for the cold rolled medium manganese steels. This paper focus on the medium manganese steel (0.15C-5Mn-Al) and investigate the ART annealing process at 675 ℃ for the medium manganese steel undergoing hot rolling and cold rolling. The microstructure evolution and mechanical property were investigated based on the scan electron microscope, electron backscatter diffraction, X-ray diffraction characteristic techniques and mechanical properties tests. The relationships between microstructure characteristics of austenites (morphology, content, grain size etc.) and mechanical properties were described. The research indicates that the product of strength to ductility (R_m×A) of medium manganese steel (0.15C-5Mn-Al) can up to 40 GPa·% undergoing reasonable ART-annealing. The morphology, content, sizes, and stability of the metastable austenites have significant effects on the strength and plasticity of the medium manganese steels. The ductility andR_m×A of medium manganese steel increased with the increase of volume fraction of metastable austenites.

Key words: austenite reverted transformation(ART), mechanical properties, microstructure, product of strength and ductility (Rm×A), medium manganese steel