Thick steel plate with high strength and low welding crack sensitivity and its production process

The present invention discloses one kind of thick steel plate with high strength and low welding crack sensitivity and its production process. The chemical composition includes C 0.06-0.09 wt%, Si 0.15-0.55 wt%, Mn 1.00-1.60 wt%, P not more than 0.015 wt%, S not more than 0.006 wt%, Ni 0.15-0.40 wt%, Cr not more than 0.30 wt%, Mo not more than 0.30 wt%, Cu not more than 0.30 wt%, V 0.02-0.06 wt%, Nb 0.005-0.05 wt% and Als 0.010-0.04 wt%, except Fe and inevitable impurities; and meets Pcm not higher than 0.20 % and Ceq not higher than 0.42 %. The production process includes two stage controlled rolling, on-line laminar flow cooling, off-line tempering and other steps. The produced steel plate has thickness up to 75mm, tensile strength not lower than 610 MPa and very low welding crack sensitivity.