Effects of different annealing time on microstructure and mechanical properties of lightweight Al-containing medium-Mn steel

Abstract

The relationship between the microstructure and mechanical properties of lightweight Al-containing medium-Mn steel with different annealing times was investigated. The results show that the microstructures of the tested steels treated by the I-Q&P process with varying times of annealing are all composed of martensite, α-ferrite, δ-ferrite, and retained austenite. With extended annealing times, the tested steel’s martensite/ferrite microstructure exhibits a variety of size and morphological changes. Simultaneously, retained austenite nucleates and grows at high-angle grain boundaries in ferrite/martensite, exhibiting multi-sized, multi-morphology, and diffuse distribution. With appropriate short annealing times, we achieved improved overall mechanical properties for lightweight Al-containing medium manganese steels than with long annealing times. It allows the tested steel to reach a tensile strength of 1000 MPa, an elongation of 48%, and the product of strength and elongation of 48 GPa·%. At this point, the tested steel shows the best overall mechanical properties.