Production method of 550MPa-grade easy-to-form weather-resistant bridge steel

The invention discloses a production method of coating-free easy-to-form weather-resistant bridge steel with yield strength of more than 550MPa grade in a service plateau environment. The steel comprises the following chemical components in percentage by mass: 0.03 to 0.05 percent of C, 0.40 to 0.50 percent of Si, 1.00 to 1.10 percent of Mn, 0.60 to 0.70 percent of Cr, 0.50 to 0.60 percent of Ni, 0.50 to 0.55 percent of Cu, less than 0.010 percent of P, less than 0.001 percent of S, 0.040 to 0.045 percent of Nb, 0.02 to 0.03 percent of Ti, 0.010 to 0.020 percent of Al, 0.005 to 0.007 percent of N, less than or equal to 0.0005 percent of B, less than or equal to 0.0002 percent of H and the balance of Fe and inevitable impurities. The produced Q550Mpa-grade weather-resistant bridge steel with the thickness of 10-40mm is a composite structure of ferrite, lath-shaped bainite and a small amount of M/A components, the yield strength is 570-635Mpa, the tensile strength is 690-760Mpa, the yield ratio is 0.81-0.84, th