# title
Strength-ductility synergy of a high chromium martensitic steel with a unique microstructure under dynamic extremes

# abstract
Plate impact shock experiments reveal metallurgical effects on the dynamic behavior and failure properties of ChromX 9120 high-strength steel. At temperatures above 1000 C, ChromX 9120 steel starts to transform from a bcc lattice (  phase) to fcc (  phase) lattice structure. Full transformation is achieved at 1100 C; the alloy reverts to bcc when cooled to room temperature. The solidsolid phase transformation (bcc-to-hcp) stress and mean Hugoniot Elastic Limit were determined to be 10.985 GPa and 1.751  0.022 GPa respectively. Precursor decay of 21% is observed between 2 mm and 12 mm thick samples, facilitated by stress relaxation. An increase in spall strength from 3.685 GPa to 3.893 GPa (regime I) is followed by a decrease to 3.100 GPa across the  to  (hcp) phase boundary (regime II). Spall strength increases thereafter to 3.301 GPa (regime III). Increases in regimes I and III are attributed to shock hardening and resistance to crack growth; the decrease in regime II is attributed to the production of new damage nucleation sites induced by the  to  transformation. Shock recovered samples show substructure boundary strengthening due to dislocation pile-ups at untransformed nano-sheets of austenite boundaries separating martensite laths. The dominant failure mechanisms are void nucleation, growth, and coalescence, but at higher peak stresses and higher magnifications, some cleavage fracture is observed. Chromium rich regions deflect and arrest propagating cracks, hindering crack growth and enhancing strength. Analytical modeling of spall fracture and precursor decay corroborate mechanisms inferred from experimental data and microstructure characterization.

# authorList[]
Williams, C. L., Hornbuckle, B. C., Mallick, D. D., Parker, T. C., Clayton, J. D., & Wilkerson, J. W.