Bulletproof steel plates: how much impact can a single plate withstand?

Impact resistance of bulletproof steel plates
The impact resistance of a steel plate depends on its material, thickness, and workmanship. For example, a 10mm thick Q235 steel plate can withstand a direct hit from a 9mm pistol bullet (kinetic energy 500J), but will significantly deform. However, using Swedish PRO500 armor steel (yield strength 1300MPa), a thickness of only 2.5mm is sufficient to achieve the same level of protection. Plates tilted at a 45-degree angle disperse the bullet's kinetic energy through ricochet, increasing protection by over 30%.

Advantages of multi-layer structures
For the same total thickness, multi-layer steel plates are more effective than a single layer. For example, a three-layer armor structure with voids dissipates energy layer by layer, causing the bullet to shatter prematurely, resulting in superior protection compared to a single layer of steel plate three times thicker. Ceramic composite armor (such as the Russian KorundVM-K plate) can even protect against 7.62mm armor-piercing incendiary rounds, but weighs up to 10 kg.

Extreme test cases
NIJ Level III ballistic steel plates (such as NP550) can withstand the impact of 7.62mm rifle bullets (kinetic energy approximately 3000J). Their tensile strength is ≥1350MPa and their hardness reaches 530-590HBW. While the 250mm homogeneous steel armor of the World War II Tiger tank was thick, modern lightweight materials (such as NP550) have achieved a 30%-40% weight reduction while maintaining the same level of protection.‌