High hardness steel used as ballistic armor: mechanical properties

Ballistic armors are designed to resist specific threats, which depend on the application. These threats can be generated by firearm projectiles or fragments from explosions with different kinetic energies. The materials usually used for this purpose are metallic, nonmetallic and composite, being evaluated by dynamic tests, such as the Hopkinson Pressure Bar and the ballistic ones at the desired level of protection. However, the material can be previously evaluated by traditional mechanical tests, such as impact and surface hardness tests, classifying it as a material that can be used in ballistic protection. Also, during of serial production of military combat vehicles, the quality control of the applied material can be done by mechanical tests like the mentioned above to verify compliance with the established requirements. Due to its cost / ballistic resistance ratio, steel is still the most used material to produce of combat vehicles. There are international standards that show the minimum mechanical properties that a steel need to get specific ballistic protection. The objective of this work was to evaluate the compliance of a high hardness steel, produced by Brazilian steel company, proposed for the production of military vehicles with protection level up to ammunition 7.62 mm, through the impact, hardness and bending tests with the MIL-DTL-46100E. The analysis of the fracture surface of the samples tested by Charpy impact was carried out to correlate the mechanical properties of the material with the fracture mode. The results obtained and the characterization of the fracture surface suggest that the studied steel does not have the mechanical behavior suitable for the use in combat vehicles, been necessary to prove it through the ballistic test.