700MPa-tensile strength steel for large heat input welding structure and manufacturing method thereof

The invention provides 700MPa-tensile strength steel for a large heat input welding structure and a manufacturing method thereof. The 700MPa-tensile strength steel for the large heat input welding structure comprises the components: 0.04-0.08 percent of carbon (C), 0.05-0.5 percent of silicon (Si), 1.40-1.85 percent of manganese (Mn), 0.2-0.4 percent of chromium (Cr), 0.010-0.060 percent of niobium (Nb), 0.005-0.03 percent of titanium (Ti), 0.02-0.04 percent of vanadium (V), 0.10-0.30 percent of copper (Cu), 0.10-0.40 percent of nickel (Ni), 0.10-0.30 percent of molybdenum (Mo), 0.0020-0.0050 percent of zirconium (Zr), 0.015-0.050 percent of aluminum (Al) and the balance of ferrum (Fe) and inevitable impurities. The manufacturing method comprises smelting, continuous casting and rolling. The temperature of heating before rolling is 1150-1230 DEG C; the rolling temperature of a recrystallization zone is not lower than 1000 DEG C; the rolling temperature of a non-recrystallization zone is 830-930 DEG C; the time of relaxation after rolling is 10-120s; the cooling speed is 3-30 DEG C/S; the final cooling temperature is 380-500 DEG C; and then, air cooling and tempering are carried out. The 700MPa-tensile strength steel for the large heat input welding structure has a reasonable component design and a simple process; thermal refining is not needed; the welding performance of a product is good; preheating is not needed before welding; thermal treatment is not needed after welding; and a heat affected zone has very high toughness.