Effect of peak stress and deformation history on the dynamic tensile behavior of a dual phase steel

The effect of peak stress and deformation history on the spall strength and associated microstructure evolution in a dual phase (50% α, 50% γ) stainless steel has been investigated. Symmetric plate impact experiments using a single stage gas- gun were performed at peak stresses in the 3.0-6.0 GPa range, pulse duration and strain rate were kept constant in all tests. The steel specimens tested were in as-received and pre-compressed (∼25% true strain) conditions. Microstructural examinations were performed using optical Microscopy and Electron Backscatter Diffraction and micro-hardness indentations. Results indicate that peak stress influences the spall strength, whereas the Hugoniot elastic limited is primarily affected by the deformation history. The spall damage, in the form of coalesced voids and cracks, is mainly accommodated by the ferrite phase, whereas the austenite phase does not experience considerable deformation. Furthermore, it is observed that the ferrite/austenite phase boundaries work as barriers for the spall damage.