Low-alloy high-strength middle-thickness plate capable of utilizing self-tempering waste heat to improve toughness and preparation method of low-alloy high-strength middle-thickness plate

The invention discloses a low-alloy high-strength middle-thickness plate capable of utilizing self-tempering waste heat to improve toughness and a preparation method of the low-alloy high-strength middle-thickness plate. The low-alloy high-strength middle-thickness plate capable of utilizing self-tempering waste heat to improve toughness is prepared from the following chemical components in percentage by weight: 0.03-0.09% of C, 0.10-0.35% of Si, 0.80-1.7% of Mn, not greater than 0.015% of P, not greater than 0.0020% of S, 0.010-0.050% of Nb, 0.010-0.050% of V, 0.005-0.030% of Ti, 0.15-0.50% of Cr, 0.05-0.20% of Mo, and the balance of Fe and inevitable impurities. The preparation method of the low-alloy high-strength middle-thickness plate comprises the following steps: compounding other alloy elements by virtue of a reasonable low-carbon component design and a low-sulfur-phosphor smelting process so as to improve the quenching degree of the middle-thickness plate; and adopting a TMCP (thermal mechanical control processing) process to roll, and controlling separation of carbide and nitride of V by virtue of a reasonable heap-cooling process after controlled cooling, and releasing rolling stress. The low-alloy high-strength steel plate texture obtained by the preparation method disclosed by the invention is a mixed texture of acicular ferrite and granular bainite, wherein the original austenite crystal grains are uniform and fine. The preparation method disclosed by the invention is stable in production process, strong in operability, low in cost and high in performance.