1 Define
Spheroidizing Agent is an additive used to improve the structure of cast iron and promote the transformation of graphite form from flake or irregular to spherical. It is mainly used in the production process of ductile iron, by adding specific elements or alloys to the liquid iron, reduce the surface energy of graphite growth, so that it is easier to form a ball, thereby improving the mechanical properties of cast iron.
Concept of spheroidizing agent
2. Principle of action
The role of nodulator is mainly based on the following aspects:
- Reduce sulfur and oxygen content: sulfur and oxygen are the inhibiting elements of graphite nodularization, and the rare earth elements (such as lanthanum, cerium, etc.) or active metals (such as magnesium) in the nodularization agent can react with sulfur and oxygen to form stable compounds and reduce the interference of these elements on nodularization.
- Change the nucleation process of graphite: magnesium (Mg), calcium (Ca), rare earth (RE) and other elements in the spheroidizer can affect the nucleation of graphite, so that it tends to grow spherical during the crystallization process, rather than sheet or vermicular.
- Optimization of matrix structure: After spheroidization, the matrix structure of cast iron changes from ferrite + flake graphite of gray cast iron to pearlite + spherical graphite, which significantly improves the strength, toughness and wear resistance of cast iron.
Concept of spheroidizing agent
3. Main spheroidizing elements and their roles
Spheroidizing agents usually consist of the following elements or alloys:
- Magnesium (Mg) : It is the most common spheroidizing element, which can effectively promote the spheroidization of graphite, but its volatility is large, and the content needs to be precisely controlled when used.
- Rare earth elements (Re, such as lanthanum La, cerium Ce) : play an auxiliary role in the spheroidization process, can improve the spheroidization effect of magnesium, reduce the decay rate, and improve the stability of castings.
- Calcium (Ca) : can reduce the burning loss of magnesium, improve the nodularization efficiency, and improve the casting performance of ductile iron.
- Strontium (Sr) : It can replace magnesium in some applications for the production of special ductile iron.
Concept of spheroidizing agent
4. Common types of spheroidizing agents
According to different application needs and production conditions, spheroidizing agents are usually in the following alloy forms:
- Magnesium alloy (such as Fe-Si-Mg alloy) : contains a certain proportion of silicon (Si), which can reduce the volatility of magnesium and improve the process performance of adding iron liquid.
- Rare earth magnesium alloy (such as Re-Mg alloy) : containing rare earth elements, suitable for the production of highly demanding ductile iron, can improve the resistance to nodularity decline.
- Magnesium - calcium alloy: suitable for specific casting conditions, can provide better spheroidization and inoculation effect.
Concept of spheroidizing agent
5. Factors affecting the effect of spheroidizing agent
The effect of spheroidizing agent is affected by many factors, including:
- The composition and addition amount of spheroidizing agent: different contents of magnesium and rare earth will affect the degree of spheroidization and the final graphite form.
- The composition of liquid iron: the content of sulfur, oxygen and carbon equivalent (CE value) in liquid iron have a great influence on the effect of nodularization treatment.
- Nodularization process: including nodulating agent adding method, treatment temperature, stirring method, etc., will affect the final nodularization rate.
- Decline phenomenon: nodularization will decline with time, and the casting time should be reasonably controlled in the production process of ductile iron to maintain the best nodularization effect.
Concept of spheroidizing agent
6. Typical applications
Spheroidizing agent is mainly used in the production of ductile iron, widely used in the following industries:
- Automotive manufacturing: such as engine cylinder block, crankshaft, steering knuckle and other key components.
- Pipeline engineering: ductile iron pipes are widely used in water supply and sewage pipelines because of their high strength and corrosion resistance.
- Mechanical manufacturing: Ductile iron because of its excellent toughness and wear resistance, often used in gear, valves, pump body and other mechanical parts.
Spheroidizing agent is an indispensable key material in the production of ductile iron. Its main function is to improve the mechanical properties and service life of cast iron by controlling the form of graphite. Reasonable selection of nodulating agent and optimization of nodulating process are important factors to ensure stable quality of nodular cast iron.
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