Enhancement of ballistic performance enabled by boron-doping in subzero-treated (ferrite+austenite+martensite) triplex lightweight steel

Abstract

Investigations of dynamic deformation and ballistic performance of ultra-high-strength lightweight steels for steel armor applications have not been conducted to date. In this study, effects of boron(B)-doping on ballistic performance were explored in subzero-treated Fe-0.3C-9Mn-5Al and Fe-0.3C-9Mn-5Al-0.005B (wt%) lightweight steels in relation to band structures and B segregation. The dynamic deformation and adiabatic shear band (ASB) formation behaviors were examined by a Hopkinson pressure bar (SHPB). The band structure is critical in inhibiting ASB propagation, as it is continuously blocked at tempered-martensite/ferrite boundaries. The crack propagates along the embrittled ASB and penetrates into tempered-martensite/ferrite boundaries, producing delamination of elongated grains in the undoped steel. On the other hand, the delamination does not occur in the B-doped steel because the segregation of solute B at prior austenite grain boundaries enhances the grain-boundary cohesion. Thus, the B-doped steel outperforms conventional rolled homogeneous armor steels and the undoped steel as well, providing a significant deal of potential for developing excellent ballistic-performance lightweight steel armors.