Thick steel plate with excellent low-temperature toughness and Rm structure of 630MPa grade and production method of thick steel plates

The invention discloses a thick steel plate with excellent low-temperature toughness and Rm structure of 630MPa grade. The thick steel plate comprises the following components in percentage by weight: 0.04-0.08 percent of C, 0.10-0.25 percent of Si, 1.00-1.50 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.20-0.60 percent of Cu, 0.15-0.35 percent of Ni, 0.20-0.40 percent of Mo, 0.032-0.090 percent of Nb, 0.008-0.030 percent of Ti and less than or equal to 0.060 percent of Als. The method comprises the following production steps: smelting, performing continuous casting to obtain the billet, and heating the casting blank; performing hot rolling; and cooling according to the temperature sections. According to the thick steel plates and the production method disclosed by the invention, the KV2 at the temperature of 40 DEG C below zero is more than or equal to 200J, the tensile strength Rm is between 630 and 780MPa, the yield ratio ReL/Rm is less than or equal to 0.85, the KV2 at the temperature of 40 DEG C below zero is more than or equal to 200J, the fibrous fracture surface ratio of an impact sample is more than or equal to 90 percent, and the carbon equivalent and cold crack sensitivity coefficient are low, so that the weldability of steel is improved. Moreover, the steel can be welded by adopting linear energy of more than 34kJ/cm under the condition that the welding quality is guaranteed.