Low welding crack sensitivity off-line tempering super thick steel plate and manufacturing method thereof

The invention provides a low welding crack sensitivity off-line tempering super thick steel plate and a manufacturing method thereof. The steel plate comprises 0.06%-0.11% of C, 0.15%-0.40% of Si, 1.40%-1.70% of Mn, 0.10%-0.30% of Ni, 0.10%-0.30% of Mo, 0.10%-0.25% of Cu, 0.03%-0.05% of Nb, 0.010%-0.025% of Ti, 0.015%-0.045% of Als and the balance of Fe. The method comprises steps of: smelting, casting, hot rolling and heat treatment; and the parameters are as below: heating temperature of 1160-1200 DEG C; billet heating time no less than billet thickness (cm) * 11min / cm; single pass reduction higher than 10% in a recrystallization stage; finish rolling temperature higher than Ar (50-150) DEG C and single pass reduction higher than 15% in a non-recrystallization stage; steel reheating temperature of 950-960 DEG C, insulation time of 2.5min / mm; quenching, tempering temperature of 610-630DEG C; and insulation time of 4min / mm. The steel provided by the invention does not contain B; the alloy has low cost; and a single continuous casting billet can be used to produce 610 MPa grade low welding crack sensibility off-line tempering super thick steel plate.