Localised shear banding in Weldox steel plates impacted by projectiles

Results from metallurgical investigations of Weldox 460 E, 700 E and 900 E steel plates impacted by hardened steel projectiles are presented. The strength is considerable higher for Weldox 700 E and 900 E than for Weldox 460 E, while the opposite is true regarding ductility. Penetration tests on the different alloys using blunt projectiles have shown that the ballistic limit velocity decreases with increasing yield strength, while in similar tests with conical and ogival projectiles the ballistic limit velocity increases with increasing yield strength. In a preliminary metallurgical study, only deformed shear bands were observed in 12 mm thick Weldox 460 E plates, while intense white etched shear bands were obtained in both Weldox 700 E and 900 E targets. The latter suggests that a phase transformation has occurred in these materials during penetration. However, based on detailed SEM and TEM studies of the localised shear zones, it was found difficult to prove such behaviour. Therefore, the authors believe that even though white shear bands were observed, the material inside the localised zone may not have reached the temperature necessary for a phase transformation from tempered to untempered martensite. In contrast, based on the TEM study, acicular ferrite and martensite twins were observed in the shear band in a 20 mm thick Weldox 460 E steel plate impacted by a blunt projectile. This strongly suggests that a phase transformation has occurred in the thicker Weldox 460 E steel plate.