Inoculation treatment refers to adding a small number of other substances to the liquid metal during the solidification process to promote nucleation, inhibit growth, and achieve the purpose of refining grains. Traditionally, adding additives to cast iron is called inoculation treatment; adding additives to non-ferrous alloys is called metamorphic treatment. Essentially, inoculation treatment mainly affects nucleation and promotes grain dissociation, while metamorphic treatment changes the crystal growth mechanism (inhibits growth), thereby affecting the crystal morphology.
When it comes to the inoculation of cast iron, we have to mention the inoculant. Inoculant is a substance that can promote graphitization, reduce the tendency of white mouth, improve the morphology and distribution of graphite, increase the number of eutectic groups, and refine the matrix structure. It has a good effect in a short time (about 5-8 minutes) after inoculation treatment. It is mainly suitable for general occurrence or late instantaneous inoculation in various situations.
Inoculation in Grey Cast Iron
The mechanical properties of gray cast iron depend to a large extent on its microstructure. Gray cast iron without inoculation treatment has unstable microstructure, low mechanical properties and white cracks are prone to appear on the thin wall of the casting. To ensure the consistency of casting quality, inoculation in grey cast iron is essential.
The inoculant used in cast iron inoculation treatment is very small, has little effect on the chemical composition of cast iron, but has a great effect on its microstructure, so it can improve the mechanical properties of gray cast iron, and also have a significant impact on its physical properties. A good insemination treatment has the following effects:
- Strongly increase the graphitized core, refine the graphite, promote the obtaining of A-type graphite in the gray iron castings, and improve the strength. For the ductile iron castings, the graphite in the ductile iron can be made small and round, and the spheroidization grade is improved.
- The inoculant can effectively reduce the subcooling degree of molten iron, promote the precipitation of graphite, significantly reduce the tendency of white mouth, reduce the relative hardness, and improve the machining performance of castings.
- Strong anti-recession ability, the anti-recession time is twice that of 75 silicon, and the addition amount of silicon barium inoculant is lower than half of 75 ferrosilicon inoculant while preventing the associated spheroidization recession.
- The wall thickness sensitivity is small, the cross-section uniformity is improved, and the shrinkage tendency is reduced.
- The chemical composition is stable, the processing particle size is uniform, and the composition and quality deviation are small.
- Low melting point (below 1300°), easy to absorb and melt during inoculation treatment, and very little scum.
Four Common Inoculants for Cast Iron
Ferro silicon Inoculant (FeSi)
| Application | It is suitable for the production of HT200, HT250, HT300, and other grades of gray iron castings. Due to its poor resistance to the recession, it is not suitable to use castings with large wall thickness differences and long pouring times without using the instantaneous inoculation process. |
|---|---|
| Dosage | 0.2%-0.4%, the instantaneous inoculation dosage can be ≤0.2%, and the dosage of high grades can be appropriately increased. |
Barium Silicon Inoculant (BaSiFe)
| Application | It is suitable for the production of various grades of gray iron castings. This kind of inoculant has a strong anti-recession ability and is suitable for large and thick-walled castings with long pouring time. |
|---|---|
| Dosage | About 0.3%. |
Silicon strontium inoculant (SrSiFe)
| Application | This type of inoculant has a strong whitening reduction ability, good cross-sectional uniformity, and anti-recession ability, and does not increase the number of eutectic groups. It is suitable for thin-walled castings, especially for castings that require shrinkage penetration. |
|---|---|
| Dosage | 0.2%-0.3% |
Calcium silicon carbide inoculant (TG-1)
| Application | This kind of inoculant has a high melting point and strong graphitization ability, which is conducive to obtaining uniformly distributed and fine A-type graphite, and is suitable for various gray iron castings under high temperature melting. |
|---|---|
| Dosage | About 0.3%. |