yvonne@nydcasting.com 
1. The sulfur content and other trace elements of the original iron liquid should not be too high.
If the sulfur content and other trace elements of the original iron liquid are too high, more spheroidizers or spheroidizers with higher rare earth content will be needed, so the cost of the spheroidizer will increase. In addition, too much spheroidizer will cause more slag, which is not conducive to the stability of casting quality. Too much rare earth content will easily produce fragmented graphite on large-section castings.
2. Stability of spheroidization.
The spheroidization process is a key process in the production process of ductile iron. Only when the spheroidization process is stable can the quality of the casting be stable. For different products, different sulfur content of the original iron liquid, how much spheroidizer, inoculant, etc. should be added should be written into the operation instructions and strictly implemented.
3. Avoid long waiting time.
After spheroidization and inoculation treatment, pouring should be carried out immediately. Because with the extension of time, the residual magnesium will burn and the inoculation effect will decline.
4. Avoid excessive residual magnesium content.
A higher residual magnesium content will increase the shrinkage tendency of the casting. For general ductile iron, the residual magnesium content (mass fraction) should be controlled at 0.035% to 0.045%, and for high-nickel ductile iron, the residual magnesium content should be controlled at 0.06% to 0.07%.
5. Use better inoculants for castings with higher requirements.
For wind power parts, high-speed rail parts, etc. with higher requirements, a flow-based inoculant with a stronger inoculation effect should be selected, which can significantly increase the number of graphite balls and make the graphite balls round.
6. Choose a suitable spheroidizer.
When choosing a spheroidizer, the following factors should be considered:
① Spheroidizing temperature:
If the spheroidizing temperature is >1480℃, the spheroidizing reaction will be more intense, resulting in a lower magnesium absorption rate. In order to make the spheroidizing reaction stable, a spheroidizer with a relatively high calcium content can be selected. If the spheroidization temperature is <1480℃, a spheroidizer with a relatively low calcium content can be used.
② Processing bag size:
If the height-to-diameter ratio of the processing bag is 1:1, the loss of magnesium vapor will lead to a decrease in the magnesium absorption rate. It is recommended to use a spheroidizer with a higher calcium content. If the height-to-diameter ratio of the processing bag is 2:1, the spheroidization reaction will be relatively stable, the magnesium vapor will diffuse into the molten iron, and the magnesium absorption rate will be improved.
③ Spheroidization treatment process:
If the cover bag method is not used, the smoke generated by the spheroidization reaction will enter the atmosphere and produce a dazzling white light. In order to make the spheroidization reaction stable, a spheroidizer with low magnesium and high calcium can be used. If the cover bag method is used, the molten iron will not splash and less smoke will be generated. A spheroidizer with high magnesium and low calcium can be used to reduce the amount added and reduce the spheroidization cost.
④ Processing weight:
If the weight of the molten iron to be treated is less than 500kg, a spheroidizer with a smaller particle size can be used. It is recommended to use a spheroidizer with a particle size of less than 12mm. If the weight of the treated molten iron is between 500 and 1,000 kg, a spheroidizer with a larger particle size, such as a spheroidizer with a particle size of 3 to 25 mm, can be used. If the weight of the treated molten iron is greater than 1,000 kg, a spheroidizer with a particle size of 4 to 32 mm can be used.
⑤ Silicon content:
If the casting yield is low or scrap rates are high, increasing recycled materials and scrap steel in the melt is necessary. When strict silicon control is required and inoculation cannot be further reduced, a low-Si spheroidizer allows 8–15% more recycled material, lowering foundry costs.
⑥ Sulfur content of molten iron:
If molten iron has high sulfur, skipping desulfurization requires a high-Mg, high-RE spheroidizer with a higher addition rate. If the sulfur content of molten iron is low, a spheroidizer with low magnesium and low rare earth can be used, and the amount added will be lower. The cost of a spheroidizer with low magnesium and low rare earth will also be cheaper.