The main function of rare earth magnesium ferrosilicon nodulator is to promote graphite nodularization, that is, to transform flake graphite into spherical graphite in cast iron. This transformation can significantly improve the mechanical properties of cast iron, resulting in higher strength, toughness and wear resistance.
Its principle of action mainly involves the interaction of elements, chemical reaction, graphite nucleation process and inhibition of the formation of flake graphite, the specific principle is as follows:
Principle of rare earth magnesium ferrosilicon spheroidizing agent
1. Spheroidization of magnesium (Mg)
Magnesium is the most important element in the spheroidization process, and its main functions are as follows:
- Reduce the surface energy of graphite and promote the spheroidization of graphite.
- Change the way of carbon precipitation in hot metal, inhibit the formation of flake graphite, and make graphite grow in spherical form.
- React with sulfur (S) and oxygen (O) to reduce the adverse effects of sulfur and oxygen on spheroidization.
- Enhancing the surface tension of molten iron is beneficial to the spherical growth of graphite.
Principle of rare earth magnesium ferrosilicon spheroidizing agent
2. The role of rare earth elements (RE, Ce, La, etc.)
Rare earth elements (such as cerium Ce, lanthanum La, neodymium Nd, yttrium Y) have high activity, and play a role in assisting spheroidization, purifying hot metal, and enhancing the ability to resist spheroidization decline during the spheroidization process:
- Reacts with sulfur and oxygen to form stable RE₂O₃ and RES, which further reduces the adverse effects of sulfur and oxygen and improves the nodularization stability.
- Improve the nucleation capacity of graphite, make spherical graphite more fine, uniform, improve the mechanical properties of castings.
- Enhance the anti-decay ability of the nodulating agent and make the nodulating process more stable.
Principle of rare earth magnesium ferrosilicon spheroidizing agent
3. The role of silicon (Si)
The main functions of silicon are:
- Promote graphitization, promote the precipitation of carbon atoms at high temperatures, and contribute to the nucleation of graphite.
- Improve the deoxidation effect of hot metal, reduce the influence of oxygen, and increase the efficiency of nodulator.
- Control the evaporation rate of magnesium, prevent the loss of magnesium too fast, improve the stability of spheroidization.
Silicon is usually used in combination with magnesium to ensure the stability of hot metal and prevent the violent volatilization of magnesium due to high temperature.
Principle of rare earth magnesium ferrosilicon spheroidizing agent
4. Role of iron (Fe)
- As a carrier element, rare earth, magnesium and silicon are more evenly distributed in hot metal.
- The melting point was adjusted to improve the solubility and reaction speed of the nodulator.
- Reduce the influence of impurities and improve the fluidity of hot metal.
Principle of rare earth magnesium ferrosilicon spheroidizing agent
5. Microscopic mechanism of spheroidization process
The essence of spheroidization is to control the way graphite grows in hot metal, and the main process is as follows:
- Add nodular agent → Magnesium and rare earth elements in hot metal react with impurities such as sulfur and oxygen to reduce the content of sulfur and oxygen.
- Change the nucleation environment of graphite → Graphite is redistributed in the hot metal and no longer grows along the sheet pattern, but precipitates out in a spherical pattern.
- Control the cooling process → Ensure that graphite grows stably in a spherical form as the molten iron cools, rather than forming a sheet or wormlike shape.
- The resulting nodular cast iron → the graphite is spherical, the iron matrix is strengthened, and the mechanical properties of the cast iron are greatly improved.
Principle of rare earth magnesium ferrosilicon spheroidizing agent
6. Factors affecting spheroidization effect
In actual production, the following factors will affect the effect of rare earth magnesium ferrosilicon nodular agent:
- Magnesium content: Magnesium content is too low, spheroidization is not complete; If it is too high, it is easy to produce magnesium oxide inclusion and affect the quality of casting.
- Rare earth content: An appropriate amount of rare earth can stabilize the spheroidization effect, but excessive may lead to coarse graphite and reduce material properties.
- Sulfur content: High sulfur iron requires higher levels of magnesium and rare earths to eliminate the adverse effects of sulfur.
- Cooling rate: Too fast cooling may lead to incomplete spheroidization of graphite, while slower cooling helps to form spherical graphite.
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