Thick protective steel plate and manufacturing method thereof

The invention discloses a thick protective steel plate and a manufacturing method thereof. The thick protective steel plate consists of the following chemical components in percentage by mass: 0.28-0.41% of carbon; 0.80% to 1.80% of silicon; 0.80% to 1.40% of Mn; 0.80-1.80% of chromium and less than or equal to 0.03% of phosphorus; less than or equal to 0.03% of sulfur, with the balance being iron and residual elements; the preparation method comprises the following steps: designing chemical components, smelting a large steel ingot, forging by using a large press, machining, quenching and tempering. The thickness of the manufactured protective steel forge piece is larger than or equal to 50 mm, the tensile strength is larger than or equal to 1350 MPa, the ductility is larger than or equal to 10%, the impact energy is larger than or equal to 40 J, and the Brinell hardness is larger than or equal to 400 HB. And the vertical impact of kinetic energy bullets of more than 1000 pounds can be protected, and the kine