Correlation of Microstructure and Ballistic Properties of Armor Plate. Part 2. Face Hardened Plate.

摘要

Laminations (elongated nonmetallic inclusions) present to an extent which would cause spalling in homogeneous plate, do not produce this result in carburized plate when tested with caliber .30 A.P. because of the protection afforded by the face. Carbides (or any other constituents which may be revealed by a Murakami etch) segregated to any extent in the grain boundaries of the case are detrimental to the extent that 75% of the brittle plate had this bad carbide condition, whereas only 25% of the acceptable plate showed a similiar condition, and each plate of this 25% showed slight petalling. The microstructures of most carburized cases ranged from a troostite to a troostito-sorbite. Martensitic structures in the core invariably caused spalling, while a uniformly distributed ferrite in sorbite was found in high ballistic nonspalling plate. Plate which passed specification had an average face hardness of 542 Brinell and an average face hardness of 372 Brinell, while plate which, although ballistically ductile, failed to meet ballistic limit requirements had an average face hardness of only 465 Brinell, and an average core hardness of 363. No relation could be found between the normal banding revealed by an Oberhoffer's etch and the ballistic properties.