Ultra-thick high-strength high low-temperature toughness steel plates for ocean platforms and production method thereof

Disclosed are ultra-thick high-strength high low-temperature toughness steel plates for ocean platforms and a production method thereof. The steel plates comprise, in weight percentage, 0.10-0.24% of C, 0.05-0.35% of Si, 0.60-1.15% of Mn, not more than 0.015% of P, not more than 0.005% of S, 0.01-0.030% of Ti, 1.45-1.75% of Cr, 0.15-0.44% of Mo, 0.80-2.50% of Ni, 0.010-0.070% of Nb, 0.020-0.080% of V, 0.02-0.06% of Alt, 0.001-0.004% of Ca, not more than 0.006% of N, 0.0007-0.0030% of B, the balance of F3 and unavoidable impurities. The steel plates have a system of C, Ni-Cr-Mo alloyed and Nb-V-Ti microalloyed, and have yield strength not smaller than 690MPa, tensile strength not smaller than 770MPa, -40 DEG C Charpy V-notch impact work no smaller than 69J, NDT (non-destructive testing) not larger than -35 DEG C, Z not smaller than 35%, and largest thickness more than 200mm. The steel plates are applicable to production of racks for ocean platforms.