Vanadium-containing carbidic austempered ductile iron and preparation method thereof

A vanadium-containing carbidic austempered ductile iron comprises the following ingredients in percent by mass: 3.20-3.70 percent of C, 2.50-3.30 percent of Si, 0.4-0.8 percent of Mn, less than or equal to 0.040 percent of P, less than or equal to 0.007 percent of S, 0.01-0.04 percent of Ce, 0.01-0.04 percent of Mg, 0.30-1.80 percent of Cr, 0.25-0.70 percent of V and the balance of Fe. The preparation method of the vanadium-containing carbidic austempered ductile iron comprises the following steps: (1), heating and smelting pig iron, steel scrap, ferromanganese and ferrovanadium; (2), placing a rare-earth magnesium nodularizer into a groove in the bottom of a ladle, placing a nucleating agent on the rare-earth magnesium nodularizer, casting for 10-30 s at the temperature of 1,350-1,430 DEG C, and cooling to obtain ductile iron; and (3), heating the cooled ductile iron to reach a temperature of 850-920 DEG C, keeping the temperature for 2-4 h, then placing the heated ductile iron into 45% KNO3+55% NaNO3 molten salt at the temperature of 280-320 DEG C, keeping the temperature for 1-3 h, taking out the ductile iron, and cooling the ductile iron to the ordinary temperature to obtain the vanadium-containing carbidic austempered ductile iron. The vanadium-containing carbidic austempered ductile iron is high in ductility and hardness and excellent in comprehensive mechanical property.