Production method of Q420-grade high-corrosion-resistance high-strength offshore structural steel

The invention discloses a production method of Q420-grade offshore structural steel with high corrosion resistance and high strength. The production method comprises the process steps of molten iron pretreatment, converter steelmaking, external refining LF, vacuum treatment RH, continuous casting, heating, rolling, controlled rolling cooling, tempering, finishing, performance inspection and ultrasonic flaw detection. The steel is characterized by comprising the following components in percentage by mass: 0.03 to 0.07 percent of C, 0.15 to 0.40 percent of Si, 0.95 to 1.05 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.003 percent of S, 0.04 to 0.06 percent of Nb, 0.01 to 0.02 percent of Ti, 0.02 to 0.05 percent of Als, 0.30 to 0.70 percent of Cu, 0.7 to 1.5 percent of Ni and the balance of Fe and inevitable impurity elements. The yield strength of the steel is larger than or equal to 420 MPa, the tensile strength of the steel is larger than or equal to 540 MPa, the low-tempera