High-strength and high-toughness nodular cast iron as well as preparation method and application thereof

The invention discloses high-strength and high-toughness nodular cast iron which comprises the following components in percentage by mass: 3.5 to 3.7 percent of C, 2.6 to 2.8 percent of Si, 0.2 to 0.4 percent of Mn, 0.35 to 0.6 percent of Cu, 0.03 to 0.06 percent of Cr, 0.006 to 0.01 percent of Sn, 0.002 to 0.006 percent of Sb, 0.03 to 0.05 percent of Mg, 0.03 to 0.05 percent of Ti, less than 0.05 percent of P, less than 0.018 percent of S and the balance of Fe and inevitable impurities. Wherein the mass ratio of Cu + Cr to Sn + Sb + Ti is 10: 1, and C + 0.3 Si is more than or equal to 4.3% and less than or equal to 4.5%. The invention further provides a preparation method of the high-strength and high-toughness nodular cast iron. The nodular cast iron prepared through the method has good strength and toughness, the tensile strength reaches 765-890 MPa, the yield strength reaches 520-590 MPa, the elongation is larger than 10%, the nodular cast iron can replace QT450-10 nodular cast iron to prepare automobile