The nodulizer acts on the nodular cast iron, which can promote the crystallization of graphite into a spherical shape, which is beneficial for obtaining nodular graphite. The strength of ductile iron is much higher than that of gray cast iron, and its toughness is better than that of malleable cast iron, which effectively improves the mechanical properties of ductile iron. In particular, the plasticity and toughness of ductile iron are improved, so that cast iron has higher strength than carbon steel.
China is rich in rare earth resources, and the commonly used nodulizer is ReSiMg nodulizer. Most foreign countries use magnesium-based nodulizers, such as pure magnesium or magnesium alloys, and a few countries use calcium-based nodulizers.
Additives added to molten iron to make graphite crystals in cast iron spherical are called nodularizers. Magnesium is the element with the strongest spheroidizing ability, and the spheroidizing effect of rare earth is relatively stable, and is not affected by other anti-spheroidizing elements. The role of calcium is stable, but the spheroidizing ability is weak, and the addition amount is large. Calcium metal is easily oxidized and cannot be used alone.
The inoculant acts on ductile iron, mainly has the following functions:
1. Promote the formation of graphitization and reduce the tendency of whitening;
2. Refining grains, reducing segregation, uniform structure, and avoiding supercooled structure;
3. Improve the mechanical strength and wall thickness sensitivity of light iron castings, so that the difference in microstructure and hardness in the thin and thick sections of castings is small;
4. It is conducive to the nucleation of eutectic clusters and increases the number of eutectic clusters;
5. Graphite in cast iron mainly exists in the form of fine and evenly distributed A-type graphite, which improves the mechanical properties of cast iron.