High-strength/toughness extra-thick low-alloy quenched and tempered steel and preparation method thereof

The invention relates to a high-strength/toughness extra-thick low-alloy quenched and tempered steel and a preparation method thereof, belonging to the technical field of low-alloy steel. The steel comprises the following chemical components in percentage by weight: 0.13%-0.17% of C, 0.15%-0.40% of Si, 1.20%-1.40% of Mn, 0.40%-0.60% of Cr, 0.30%-0.40% of Mo, 0.20%-0.40% of Ni, 0.0010%-0.0030% of B, 0.015%-0.035% of Nb, 0.035%-0.060% of V, 0.010%-0.020% of Ti, 0.020%-0.040% of Alt, 0.005%-0.010% of P, 0.002%-0.0050% of S, 0.54%-0.60% of carbon equivalent Ceq, and the balance of Fe and inevitable impurities. The steel has comprehensive mechanical properties; the steel plate has small difference and high uniformity of mechanical properties in the thickness direction; and the steel plate has the advantages of favorable internal quality and no flaw detection defects.