Correlation of Metallurgical Properties with the Low Temperature Ballistic Shock Characteristics of 1 Inch to 2 Inch Low Alloy Cast Armor Tested at Camp Shilo

摘要

A low temperature (-10 to -40 F) ballistic shock test of 1-in to 2-in cast armor is much more severe than the same test conducted at normal temperatures, all other factors remaining constant. This increase in the severity of test reveals the poor shock characteristics of borderline quality armor. Poor performance of 1-in plates associated with heterogeneous microstructures (high temperature transformation products), a high hardness level, or both. Properly heat treated low alloy cast steel of the type studied should be over approximately 330 Brinell. The heterogeneous structure was generally caused by an insufficiently drastic quench and an incomplete utilization of the alloy. The most important cause of the poor performance in the 1 1/2-in and 2-in cast plates examined was the presence of heterogeneous microstructures formed as a result of incomplete quenching, insufficient hardenability or a combination of both factors. Many of the plates could be improved materially with an improvement in the quenching technique. However the alloy content of several of the heats is insufficient to impart enough hardenability to completely quench out the 2-in plates even if a drastic quench is employed. The metallurgical tests which may be used to indicate the presence of heterogeneous structures and the resulting poor shock properties of incompletely quenched cast armor are the fracture test, V-notched Charpy impact test, and the microscopic examination.