Effect of Annealing Treatment on Mechanical Properties and Stamping Formability of Cold‐Rolled Medium‐Manganese Automobile Steel

Austenite reverse transformation (ART) and intercritical annealing (IA) are two common heat treatment processes for advanced high‐strength medium‐manganese automobile steel. In this article, the volume fraction of residual austenite, mechanical properties, formability, and microstructure of 0.1C‐5Mn automobile steel under two heat treatments are systematically studied by X‐ray diffractometer, universal tensile testing machine, scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the microstructure of the experimental steel after two annealing processes is martensite, ferrite, and residual austenite. With the increase of annealing temperature and time, the volume fraction of residual austenite increases first and then decreases. When holding at 640 °C for 20 min, the volume fraction of residual austenite reaches the maximum, and the volume fraction of residual austenite obtained by the IA process is 8.41% higher than that of the ART process. With the increase in annealing temperature and time, the yield strength decreases, the tensile strength increases gradually, and the elongation and the multiplication of strength and plastic increase first and then decrease. When holding at 640 °C for 20 min, the comprehensive mechanical properties are the best. Compared with the ART process, the yield strength of the experimental steel under the IA process is increased by 16.93%, the tensile strength is increased by 2.04%, the elongation is increased by 6.98%, and the multiplication of strength and plastic is increased by 9.17%. When holding at 640 °C for 20 min, the {100} texture of the experimental steel treated by the IA process is 18.79% lower than that of the ART process, while the {110} texture and {111} texture are 20.75% and 28.55% higher, respectively. Compared with the ART process, the IA process not only eliminates the quenching treatment but also enables the experimental steel to obtain a better comprehensive performance.