Potential of ultrafine grained materials as high performance penetrator materials

¹ Agency for Defense Development, PO Box 35-42, Daejeon 305-600, Korea
² Dept. of Mater. Sci. Eng., POSTECH, Pohang 790-784, Korea
³ Dept. of Mater. Sci. Eng., Hanbat Nat’l Univ., Daejeon 305-719, Korea

^a e-mail: ktpark@hanbat.ac.kr

Abstract

The shear formability and the metal jet formability are important for the kinetic energy penetrator and the chemical energy penetrator, respectively. The shear formability of ultrafine grained (UFG) steel was examined, mainly focusing on the effects of the grain shape on the shear characteristics. For this purpose, UFG 4130 steel having the different UFG structures, the lamellar UFG and the equiaxed UFG, was prepared by equal channel angular pressing (ECAP). The lamellar UFG steel exhibited more sharper and localized shear band formation than the equiaxed UFG steel. This is because a lamellar UFG structure was unfavourable against grain rotation which is a main mechanism of the band propagation in UFG materials. Meanwhile, the metal jet formability of UFG OFHC Cu also processed by ECAP was compared to that of coarse grained (CG) one by means of dynamic tensile extrusion (DTE) tests. CG OFHC Cu exhibited the higher DTE ductility, i.e. better metal jet stability, than UFG OFHC Cu. The initial high strength and the lack of strain hardenability of UFG OFHC Cu were harmful to the metal jet formability.