Manufacturing method of low-alloy ultrahigh-strength steel

The invention discloses low-alloy ultrahigh-strength steel. The formula of the low-alloy ultrahigh-strength steel comprises the following component of 0.30-0.35% of C, 1.0-1.5% of Mn, 1.50-1.80% of Si, less than or equal to 0.010% of S, less than or equal to 0.010% of P, 1.45-1.85% of Ni, 0.03-0.08% of Al, 0.80-1.20% of Cr, 0.08-0.15% of V, less than or equal to 0.0001% of H, less than or equal to 0.0015% of O, less than or equal to 0.010% of N, and the balance Fe and other inevitable impurities. The invention also discloses a manufacturing method of the low-alloy ultrahigh-strength steel. The manufacturing method comprises the following steps of quantitative weighing, smelting, forging, normalizing, primary tempering, quenching and secondary tempering. Compared with the existing 30CrMnSiNi2, the low-alloy ultrahigh-strength steel has the advantages that a smelting process is optimized and adjusted to be a vacuum induction and vacuum self-consumption smelting method, a steel ingot is subjected to a high-tempe