Microstructure and Mechanical Properties of Medium Manganese Steel with Different Aluminum Addition After Very Short Time Intercritical Annealing

In this work, the phase transformation, microstructure, and mechanical properties of medium manganese steels containing 1.0 and 2.5% aluminum (mass%) were investigated at different intercritical annealing (IA) temperatures (670-820 degrees C) after very short IA times (1 min) using thermodynamic simulations, scanning electron microscopy, transmission electron microscopy, x-ray diffraction and uniaxial tensile tests. The results show that with the addition of aluminum, the temperature range between A(1) and A(3) increases from 338 degrees C for 1.0% Al to 506 degrees C for 2.5% Al. The retained austenite (RA) has two different morphologies, namely polygonal and lath. Most of the RA transformed into martensite during deformation. Two types of martensite were observed: the alpha'-martensite and epsilon-martensite. The steel with 2.5% aluminum (mass%), after IA at 790 degrees C, shows the best combination of tensile properties, including a tensile strength of 982.5 MPa, an elongation of 42.96%, and tensile strength x total elongation greater than 42 GPa%.