The invention discloses a thick steel plate and a manufacturing method thereof, and belongs to the field of
ferrous metallurgy. The method comprises the following steps of molten iron KR pre-desulfuration, converter
smelting, LF refining, RH vacuum treatment, wire feeding, flexible stirring, plate blank
continuous casting, plate blank reheating, rough rolling, intermediate blank temperature holding cooling, precision rolling, ACC quick cooling, steel plate straightening and stacking
slow cooling, wherein in the plate blank reheating stage, the temperature is 1120-1220 DEG C, and the in-furnacetime is longer than or equal to 1.0 min / mm; in the rough rolling stage, the temperature is 1000-1080 DEG C, and the thickness of an intermediate blank after rolling is larger than 2.5 times that of asteel plate; in the precision rolling stage, the temperature is lower than or equal to 900 DEG C, the finish rolling temperature is 780-820 DEG C, and the total
compression ratio in the stage is larger than or equal to 60%; in the cooling stage, the finish
cooling temperature is 300-400 DEG C, and the
cooling rate is 10+ / -5 DEG C / s. The steel plate manufactured through the method comprises the following chemical components of, by
mass percent, 0.06-0.09% of C, 0.10-0.30% of Si, 1.40-1.70% of Mn, 0.020-0.060% of Al, 0.03-0.05% of Nb, 0-0.020% of Ti, 0-0.30% of Cr, 0-0.016% of P, 0-0.005% of S,0-0.080% of N and the balance Fe and inevitable
impurity elements, the carbon equivalent Ceq is equal to [C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15] and smaller than or equal to 0.42%, the
welding crack sensitivity index CEpcm is equal to [C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B] and smaller than or equal to 0.20%, and the applicable thickness of the steel plate is 40-70 mm.