Q355NHC weather-resistant steel plate and preparation method thereof

The invention relates to a Q355NHC weather-resistant steel plate and a preparation method thereof, and belongs to the technical field of steel smelting, and the weather-resistant steel plate comprises the following substances in percentage by mass: 0.12%-0.15% of C, 0.26%-0.50% of Si, 1.0%-1.40% of Mn, less than or equal to 0.025% of P, less than or equal to 0.020% of S, 0.25%-0.40% of Cu, 0.20%-0.40% of Ni, 0.40%-0.65% of Cr, 0.010%-0.020% of Nb and the balance of Fe. The preparation method comprises the following steps of molten iron pretreatment, converter combined blowing, LF refining, RH refining, continuous casting, slab heating, slab rough rolling, slab finish rolling, ACC cooling after slab rolling and slab finishing. On the basis of carbon manganese steel, a proper amount of Nb microalloy elements are added, and meanwhile, the internal quality of the plate blank is improved by controlling the steelmaking process; by optimizing the rolling process, the structure and grain size of the material are impr