Abstract
Due to their advantageous properties, there is a growing interest in developing armor steels containing fully or partially bainitic microstructures. In this study, bainitic and martensitic microstructures were obtained in rolled homogeneous armor (RHA) steel samples and their ballistic protection performances were investigated. RHA (MIL-A-12560) steel samples were subjected to isothermal heat treatments at three different temperatures, where one temperature (360 °C) was above the martensite formation start (Ms) temperature of 336 °C while the other two (320 °C and 270 °C) were below. For the assessment of the ballistic protection performance, the kinetic energy losses of the 12.7 mm bullets fired at the test samples were determined. The promising nature of the bainite microstructure was confirmed as the sample isothermally treated at 360 °C provided approximately 10% higher ballistic protection as compared to the regular RHA sample of tempered martensite microstructure. However, the ballistic performances of the isothermally treated samples decreased as the treatment temperature went below the Ms temperature. Following the ballistic tests, hardness measurements, impact tests at −40 °C, and macro- and microstructural examinations of the samples were performed. No correlation was found between the hardness and impact energies of the samples and their ballistic performances.
Highlights
There are many ballistic protection applications in which non-ferrous or even non-metallic armors are being used, there are still some applications, such as heavy armored vehicles, where steel is the main material of choice due to its advantageous combination of properties like ballistic performance, lower cost, weldability, etc
It was found that the samples with essentially bainitic microstructures provided slightly higher ballistic protection than the regular Rolled homogeneous armor (RHA) sample
This observation suggests that it may be possible to improve the ballistic performance through bainitic microstructures even in an armor steel of conventional chemical composition
Summary
There are many ballistic protection applications in which non-ferrous or even non-metallic armors are being used, there are still some applications, such as heavy armored vehicles, where steel is the main material of choice due to its advantageous combination of properties like ballistic performance, lower cost, weldability, etc. The ballistic performance of a steel is essentially dependent on its mechanical behavior under the very high rate of loading experienced at ballistic speeds [1,2]. Studying such behavior experimentally in a laboratory is very difficult. The hardness and impact test results, they are determined under very static conditions as compared to the ballistic speeds, remain as the conventional and practical indicators of ballistic performance. In addition to some ballistic performance requirements, armor steel standards such as MIL-A-12560 specify certain hardness and impact energy values [3,4,5]. Rolled homogeneous armor (RHA), which is one of the most widely used general purpose structural armor steels, meets these requirements through a tempered martensite microstructure obtained by the conventional quenching and tempering processes
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