This study presents the effect of heat treatment on the adiabatic shear band formation in the steels AISI 4340 and DIN 100Cr6, which were impacted by 7.62 mm armour piercing (AP) projectile. Adiabatic shear band formation was investigated in the steel samples having different hardness levels and thickness values. Examinations were carried out using both optical and scanning electron microscopy to see the microstructural variations apparently. Moreover, microhardness measurements were also made to correlate structure-property relationships. Results showed that transformed bands were seen in the samples having the hardness of 49 and 59 HRC but deformed bands were observed in all investigated samples. Moreover, a fine grain structure with carbide precipitates was observed in the transformed bands.