420MPa-grade weather-resistant bridge steel and production method thereof

The invention discloses 420MPa-grade weather-resistant bridge steel and a preparation method thereof. The 420MPa-grade weather-resistant bridge steel is prepared from the chemical components including, by mass, 0.05%-0.07% of C, 0.25%-0.50% of Si, 1.10%-1.70% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.28%-0.35% of Cu, 0.20%-0.30% of Ni, 0.45%-0.55% of Cr, less than or equal to 0.10% of Mo, 0.008%-0.030% of Nb, 0.010%-0.030% of Ti, 0.005%-0.015% of V, 0.020%-0.035% of Als, 0.0020%-0.0050% of Ca, less than or equal to 0.0040% of O, 0.0025%-0.0080% of N, and the balance Fe and inevitable impurities; and Nb / C+V / N is larger than or equal to 1.8 and is less than or equal to 3.5. The low-C-proper-Si and Mn-trace Nb-V-N alloying thought is adopted, the low-cost thought of high Cr and low Cu and Ni is adopted, a proper amount of Cu-Cr-Ni is added, the weather resistance is guaranteed, and the 420MPa-grade weather-resistant bridge steel which is low in cost, excellent in comprehensive performance, wide in production process window and capable of easily achieving batch industrial production is obtained, the composition system is matched with the optimized TMCP+tempering preparation technology, the requirement for the capacity of production equipment is reduced, and the steel is suitable for batch industrial production of small and medium-sized steel mills.