Influence of silicon addition on intercritical annealing process and tensile properties of medium Mn steel

This paper presents research on the equilibrium phase fractions, microstructure, and tensile properties of a 0.2C–5Mn–1.5Al (mass %) steel with 0 or 0.5 (mass %) Si addition after intercritical annealing (IA), using thermodynamic simulation, scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and uniaxial tensile testing. The research results show that the addition of 0.5 Si (mass %) has no significant effect on the equilibrium phase fraction but influences the optimal IA temperature. Different IA temperatures result in the retained austenite having different morphologies. The retained austenite in the 730 °C sample (0.5 Si) has two different morphologies—polygonal and lath—while the 760 °C sample (0 Si) has only polygonal retained austenite. The optimal tensile properties of the 0.5 Si steel are better than those of the 0 Si steel due to the solution strengthening effect of Si and the higher stability of retained austenite. The tensile properties of the investigated 0.5 Si steel are excellent, with a tensile strength of over 1 GPa, elongation over 42.00%, and strength × ductility over 42 GPa%.