Manufacturing method of 800Mpa-grade high-elongation medium-thickness steel plate

The invention discloses a manufacturing method of an 800Mpa-grade high-elongation medium-thickness steel plate. The steel comprises the following chemical components in percentage by mass: 0.12-0.20% of C, 0.10-0.50% of Si, 1.10-1.70% of Mn, less than or equal to 0.025% of P, less than or equal to 0.010% of S, less than or equal to 0.030% of Nb, 0.2-0.5% of V, 0.01-0.02% of Ti, less than or equal to 0.30% of Cu, 0.10-0.50% of Ni, 0.15-0.50% of Mo, 0.020-0.060% of Alt, 0.0008-0.0015% of B and the balance of Fe and inevitable impurities. Medium carbon microalloying component design is adopted, a slab is formed through continuous casting, and through the controlled rolling and cooling process and the follow-up heat treatment process, the strength level can reach 800 Mpa, the ductility is larger than or equal to 30%, the impact at the temperature of-40 DEG C is larger than or equal to 150 J, and the Z-direction tensile section shrinkage rate is larger than or equal to 55%. The steel plate is excellent in performa