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Introduction of nodularizer: The additive that makes graphite crystallize into sphere in cast iron is called "nodularizer". The main components of "spheroidizing agent" are spheroidizing elements, such as Mg, Ce, Ca, etc. The spheroidal graphite in nodular cast iron is produced by spheroidizing the molten iron of cast iron, which makes its strength much higher than that of gray cast iron, and its toughness better than malleable cast iron, while maintaining a series of advantages of gray cast iron. However, the "spheroidizing agent" used in nodular cast iron melting and casting can increase the tendency of "white" and hardening structure in the weld, and induce cracks in the weld and heat affected zone (especially in the fusion zone). Therefore, the weldability of ductile iron is worse than that of gray iron.  

The spheroidizing agent commonly used in China is ferrosilicon rare earth magnesium alloy. Magnesium spheroidizing agent (pure magnesium and magnesium alloy) is mostly used abroad, while calcium spheroidizing agent is used in a few countries.

The development of nodulizer plays an important role in promoting the production of nodular iron. Cerium is a very early confirmed spheroidizing agent. At that time, the source of cerium was scarce and the composition of hot metal was strict, which made it impossible for cerium nodular iron to be used in industrial production. Magnesium nodularizer makes nodular iron obtain industrial scale production and application. The development of nodularizer from pure magnesium to Mg-Ni, Mg-Cu and Mg-Si-Fe alloys promotes the expansion of nodular iron production. With the development of rare earth magnesium ferrosilicon nodulizer, nodular iron production in China is basically based on domestic resources. A series of rare earth magnesium nodular iron has been established in China, which enlarges the application scope of pig iron, improves the properties and quality of nodular iron castings, and makes nodular iron production more vigorous. The application of yttrium heavy rare earth has created conditions for the development of new composite spheroidizers. The comprehensive utilization of various spheroidizing elements will create favorable conditions for the further development and improvement of nodular iron production.

The basic requirements for spheroidizing agents are as follows.

(1) Strong ability of spheroidization;

(2) It is rich in resources, cheap and easy to melt.

(3) It has strong adaptability to various components (such as eutectic degree, sulfur content, anti-spheroidizing element and alloy element) and temperature of hot metal.

(4) The spheroidization reaction has good kinetic conditions, stable reaction, easy removal of reaction products, less dosage, less cooling, and good spheroidization process.

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