Low-cost Q690 steel plate and preparation method thereof

The invention belongs to the field of high-strength plate manufacturing, and particularly relates to a low-cost Q690 steel plate and a preparation method thereof. A proper amount of vanadium-nitrogen alloy is added into low-carbon medium-manganese molten steel, a large amount of nanoscale NV in the steel plate is promoted to be dispersed and separated out, the strength and toughness performance of the core of the high-strength plate is improved through the effect that NV promotes intracrystalline ferrite nucleation, grains are refined through large-compression-ratio rolling, quenching and tempering treatment is not needed, and the high-strength plate is obtained. The yield strength of the steel plate ranges from 702 MPa to 756 MPa, the tensile strength of the steel plate ranges from 782 MPa to 823 MPa, the ductility of the steel plate ranges from 15.6% to 18.9%, and the impact energy at the temperature of minus 40 DEG C is larger than 80 J. The use amount of expensive alloy is small, the production process is