Study of a new type ductile iron for rolling: Composition design (1)

By investigating the effects of the main elements such as Si, Mn, Mo and ausforming on the microstructure and properties, a new type ductile iron with the composition of 3.0–3.8%C, 2.9–3.4%Si, 1.6–2.1%Mn, 0.02–0.05%RE and 0.02–0.05%Mg, which has a microstructure composed of bainite, small amount of martensite, residual austenite and carbide, was developed. Contrasting to the traditional ductile iron, this new type ductile iron does not contain precious alloys, which reduces the manufacturing cost. It is found that the ratio of Si/Mn is an important parameter to the microstructure and the mechanical properties of the new type ductile iron. The favorable value for the ratio of Si/Mn is in 1.6–2.2. The ausforming is an important method to greatly improve the properties of this material. Favorable ausforming parameters with a deformation content of 20–40% and a tempering temperature of 200–300 °C were provided for this material. Performance measurements indicate that this material is of excellent general mechanical properties. The surface hardness exceeds HRC54 when the impact energy is reaching 30 J/cm2.