Vanadium-chromium microalloying large-specification 500MPa ultra-fine grain corrosion-resisting anti-seismic steel bar and preparation method thereof

The invention discloses a vanadium-chromium microalloying large-specification 500MPa ultra-fine grain corrosion-resisting anti-seismic steel bar and a preparation method thereof. The steel bar comprises, by weight percent, 0.21-0.25wt% of C, 0.45-0.55wt% of Si, 1.25-1.40wt% of Mn, 0.30-0.35wt% of Cr, 0.065-0.080wt% of V, not larger than 0.040wt% of S, not larger than 0.045wt% of P, not larger than0.0070wt% of O, 0.0165-0.0200wt% of N and the balance Fe and inevitable impurities. The preparation method of the steel bar comprises the procedures of molten steel smelting, deoxidization alloying,LF furnace refining, casting, steel blank heating and controlled rolling and controlled cooling. A certain amount of vanadium-containing pig iron is added into a tapping steel ladle to replace the expensive vanadium alloy, the V content of molten steel is increased, and the adding quantity of the vanadium alloy is reduced; in the deoxidization alloying process, a small quantity of silicon-nitrogenalloy is added, the nitrog