Knowledge

The ways in which spheroidizing agents form spheroidization cores mainly include the following points:

The core of the chemical reaction formation: During the smelting of the molten iron and the subsequent processing, the magnesium, rare earth and other elements in the spheroidizing agent will undergo chemical reactions with sulfur, oxygen and other elements in the molten iron, generating sulfides and oxides. These compounds, such as MgS, MgO, RE2O3, etc., are initially small in size and serve as substrates for the nucleation of graphite, that is, the spheroidization core.

Core growth: As the holding time of the molten iron is prolonged, especially during the pouring and filling process, these compounds will collide with each other and thus aggregate and grow larger. Although this may lead to particle coarsening, under appropriate conditions, these coarsened compounds can still serve as effective spheroidization cores.

Promoting graphite nucleation: The inoculant forms stable spheroidization cores, providing sites for the aggregation of carbon atoms. During the cooling and solidification of the molten iron, carbon atoms gather around these cores to form spherical graphite. Compared with flake graphite, these spherical graphite particles have a reduced tendency to fracture the matrix, thereby enhancing the performance of the cast iron.

It should be noted that the formation of spheroidized nuclei is a complex physicochemical process involving chemical reactions, physical aggregation, and changes in the conditions of the molten iron.

I. Chemical reaction to form initial nuclei

Reactions of magnesium with sulfur and oxygen:

The magnesium in the inoculant reacts chemically with sulfur and oxygen in the molten iron to form magnesium sulfide (MgS) and magnesium oxide (MgO). These compounds are initially small in size and serve as substrates for the nucleation of graphite, that is, the initial spheroidization nuclei.

The role of rare earth elements:

Rare earth elements (such as cerium, lanthanum, etc.) also combine with sulfur and oxygen in the molten iron to form stable rare earth sulfides and rare earth oxides. These compounds also have the potential to serve as nuclei for graphite formation.

II. Physical Agglomeration and Core Growth

Particle Collision and Aggregation:

As the holding time of the molten iron increases, especially during the pouring and filling process, the initial spheroidization core particles will collide with each other in the molten iron, leading to aggregation and enlargement. This process follows certain physical and chemical principles, such as particle coarsening conforming to the Wagner equation.

Temperature and concentration fluctuations:

During the inoculation treatment, many dispersed high-Si micro-regions and supersaturated C atom micro-groups are formed in the melt. In addition, many temperature fluctuations also occur. The inhomogeneities in composition and temperature (also known as concentration fluctuations and temperature fluctuations) have a positive promoting effect on the nucleation of graphite. However, as the liquid state time increases, the concentration fluctuation phenomenon gradually disappears, and the temperature fluctuation also gradually decreases over time, which will affect the number and size of the newly formed spheroidization cores.

III. The Influence of Molten Iron Conditions on Core Growth

Molten iron temperature:

The temperature of molten iron is a crucial factor affecting the growth of spheroidization cores. An appropriate temperature is conducive to the progress of chemical reactions and the aggregation and growth of particles.

Chemical composition:

The chemical composition of the molten iron, especially the content of elements such as sulfur and oxygen, directly affects the spheroidization effect of the spheroidizing agent. Molten iron with low sulfur and low oxygen content is conducive to the formation of more spheroidization cores and promotes the growth of these cores.

Treatment process:

The spheroidizing treatment process also has a significant impact on the formation and growth of spheroidizing cores. A reasonable treatment process can ensure that the spheroidizing agent fully functions, forming stable and evenly distributed spheroidizing cores.

IV. Conclusion

The process by which inoculants promote the growth of spheroidization nuclei is a complex one involving chemical reactions, physical aggregation, and changes in the conditions of the molten iron. Through the use of a reasonable inoculant formula and treatment process, the formation and growth of spheroidization nuclei can be effectively controlled, thereby obtaining high-quality ductile iron.

It should be noted that the above analysis is based on the general behavioral principles of the inoculant in the molten iron. The specific process may vary due to differences in the type of inoculant, the conditions of the molten iron, and the treatment process. In practical applications, adjustments and optimizations need to be made according to specific circumstances.​​​​​​​

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