Abstract: A newly designed Fe-9Mn-2Al-0.3C medium Mn steel was subjected to quenching and partitioning (Q&P) treatment with different parameters. The effects of heating temperature (640-860 ℃), quenching medium temperature (60-140 ℃), and quenching time (10-300 s) on the microstructure and properties of the medium Mn steel were studied, and compared and analyzed with the microstructure and properties of the steel treated by quenching and tempering (QT) process. The results show that the microstructure of the steel is lath martensite and block remained austenite treated by fully austenitizing Q&P process, and the best strength and plasticity can be obtained, with a tensile strength of 1408.3 MPa, elongation after fracture of 15.2%, and product of strength and elongation of 21.4 GPa·%, after 860 ℃×300 s heating +60 ℃×300 s quenching+350 ℃×180 s partitioning. The quenching medium temperature has a little effect on the microstructure and grain size of the tested steel, mainly affecting the content of retained austenite. The quenching time has little effect on the microstructure of the tested steel, but a longer quenching time is beneficial for the diffusion of carbon element, making the retained austenite rich in carbon and stable, thereby improving the plasticity of the tested steel. By comparing the Q&P process with the QT process, it is found that carbon elements can diffuse into austenite more effectively during the Q&P stages, making retained austenite more stable. The steel treated by Q&P process has higher retained austenite content and better plasticity.

Key words: Al-containing medium Mn steel, quenching and partitioning (Q&P), microstructure, mechanical properties