Suppression of adiabatic shear band formation by martensitic transformation of retained austenite during split Hopkinson pressure bar test for a high-strength bainitic steel

In this study, a high-strength bainitic steel was fabricated and austempered at 350 °C for 15 min, 90 min, and 24 h to control the volume fraction of retained austenite (RA) while keeping an appropriate hardness level. Their dynamic compressive properties were investigated in relation to the ASB formation and cracking by the SHPB. The specimen austempered for 90 min showed the highest volume fraction of RA along with the highest compressive properties. This specimen also possessed the high resistance to form a transformation-ASB (tASB), which was attributed to the active deformation-induced martensitic transformation of RA. Since the applied dynamic energy was consumed by the martensitic transformation as well as the ASB formation, the active transformation effectively delayed the critical strain for initiating formation. Therefore, this critical strain concept, which was well correlated with dynamic compressive properties, would be an important key factor for suppressing the ASB formation and for improving the ballistic performance.