High-yield 550MPa-grade steel and manufacturing method thereof

The high-yield 550MPa-grade steel is prepared from the following raw materials in percentage by mass: 0.15 to 0.18 percent of C, 0.20 to 0.40 percent of Si, 1.3 to 1.5 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.050 percent of Alt, less than or equal to 0.0080 percent of N, 0.015 to 0.020 percent of Nb, 0.040 to 0.060 percent of V and the balance of Fe and inevitable elements. According to the high-yield 550MPa-grade steel and the manufacturing method thereof, the proportion of C, Si, Mn, P, S, V and N in the steel is adjusted, the size of a plate blank is adjusted, meanwhile, controlled cooling is adopted, the high yield of the 550MPa-grade steel can be increased, the production cost is reduced, the 550MPa-grade steel produced through the method has the advantages that the yield of the 550MPa-grade steel is increased, and the yield of the 550MPa-grade steel is increased. The yield strength is greater than or equal to 550MPa, the t