High strain rate shear evaluation and characterization of AISI D2 tool steel in its hardened state

High strain rate mechanical testing on fully hardened AISI D2 tool steel (a t 62 HRc) was performed utilizing the Compressive Split Hopkinson Bar techn ique (CSHB) incorporating a punching shear strain state. The high strain ra te conditions were comparable to those encountered in machining processes, with shear strain rates on the order of 5 x 10(4) s(-1) and shear strains i n excess of unity (100% mm/mm). The tests were performed at various initial temperatures ranging from 296-873 K to investigate the flow stress behavio r of the hardened tool steel as a function of temperature. The high strain rate experimental shear stress-strain data was used to fit the flow stress by; i) an empirically based constitutive law in the form proposed by Johnso n and Cook; as well as, (ii) a physically based constitutive law proposed b y Zerilli and Armstrong which accounts for strain, strain rate, and tempera ture dependence of flow stress. The data incorporated the adiabatic tempera ture rise in the shear zone and was used in the constitutive law modeling. The deformed microstructure was investigated using optical and scanning ele ctron microscopy to determine the extent of the shear localization zone and the final fracture mode.