Microstructure and mechanical properties of hot-rolled medium-Mn steel containing 3% aluminum

The present investigation was made to study the variations of microstructure and mechanical properties of hot-rolled 3%Al containing medium-Mn steel at different intercritical annealing temperatures. The results show suitable intercritical annealing could obtain a duplex microstructure of lathy retained austenite (RA) and bimodal size distributed lathy ferrite. The ultimate tensile strength (UTS) increases while the yield strength decreases with increasing annealing temperature, and the total elongation (TEL) initially increases, but then notably decreases with increasing annealing temperature after a maximum value at 730-750 °C. An excellent combination of UTS of 922 MPa, TEL of 61% and UTS×TEL of 56 GPa% could be obtained when annealed at 750 °C. These values are significantly superior to a number of previously studied medium-Mn steels with similar Mn content. The stability of RA decreases with increasing annealing temperature primarily due to the increase of the RA size. It is suggested that the RA with an intermediated size of lath width of ~0.51-0.70 µm has suitable stability from the standpoint of obtaining large TRIP effect during tensile testing.