High-strength structural steel S690QL (QL1) medium-thickness plate and production method thereof

The invention relates to a high-quality and high-yield-strength structural steel S690QL (QL1) medium-thickness plate and a production method thereof. The S690QL (QL1) structural steel plate comprises the following chemical components in percentage by mass (unit: wt%): 0.10-0.20 of C, 0.30-0.70 of Si, 1.35-1.65 of Mn, P not more than 0.010, S not more than 0.005, microalloying elements (V+Nb+Ti+Cr+Ni+Mo+B) not more than 3.2, Als not more than 0.050, and the balance of Fe and residual elements. The production method comprises such process control as KR molten iron pretreatment, converter smelting, LF refining, vacuum refining, pouring, casting blank heating, rolling, slow cooling and heat treatment. Through reasonable chemical component design, the LF+VD process guarantees the cleanness of steel quality; through effective implementation of such processes as heating, rolling and tempering treatment, the S690QL (QL1) structural steel plate with a thickness of below 150 mm, guaranteed performance, guaranteed flaw detection and high yield strength is successfully researched; the yield strength is controlled within 650-780 MPa; the tensile strength is controlled within 740-930 MPa; the elongation is controlled within 15-25%; and the V-60 DEG C longitudinal impact power is controlled within 143-340 J.