Effect of Cr Addition and Intercritical Annealing Conditions on Microstructure and Mechanical Properties of A Medium Manganese Steel

Advanced high-strength steels are attracting the attention of the automotive industry as materials that offer both lightness and safety due to their high strength and good formability properties. Within this group of steels, medium-manganese steels stand out in new-generation engineering applications by offering an excellent balance of strength-ductility thanks to the transformation-induced plasticity effect. In this study, the effects of Cr addition and intercritical annealing conditions on microstructure and mechanical properties of medium manganese steels were investigated. 45 mm thick medium Mn steel plates (0.16C-5.5Mn) with 0, 0.4, 0.8, 1.2 wt.% Cr additions were manufactured by casting and then reduced to 5 mm thickness by hot pressing and hot forging. The samples were annealed in the intercritical region (650 °C) and then cooled either in air or by water quenching. Microstructural characterization was performed using optical and scanning electron microscopy. The phase composition and volume fraction of retained austenite were determined through X-ray diffraction and energy-dispersive spectroscopy. The results showed that the volume fraction of the retained austenite phase increased with rapid cooling and Cr content. In the tensile tests, it was observed that the Cr in the steel composition improved the tensile strength-total elongation combination. The best combination (32 GPa.%) was obtained in the 1.2% Cr added sample by water quenching after intercritical annealing.