Enhancement of ballistic performance enabled by transformation-induced plasticity in high-strength bainitic steel

High-strength bainitic steels have created a lot of interest in recent times because of their excellent combination of strength, ductility, toughness, and high ballistic mass efficiency. Bainitic steels have great potential in the fabrication of steel armor plates. Although various approaches and methods have been conducted to utilize the retained austenite (RA) in the bainitic matrix to control mechanical properties, very few attempts have been conducted to improve ballistic performance utilizing transformation-induced plasticity (TRIP) mechanism. In this study, high-strength bainitic steels were designed by controlling the time of austempering process to have various volume fractions and stability of RA while maintaining high hardness. The dynamic compressive and ballistic impact tests were conducted, and the relation between the effects of TRIP on ballistic performance and the adiabatic shear band (ASB) formation was analyzed. Our results show for the first time that an active TRIP mechanism achieved from a large quantity of metastable RA can significantly enhance the ballistic performance of high-strength bainitic steels because of the improved resistance to ASB formation. Thus, the ballistic performance can be effectively improved by a very short austempering time, which suggests that the utilization of active TRIP behavior via tuning RA acts as a primary mechanism for significantly enhancing the ballistic performance of high-strength bainitic steels.