Every foundry producing ductile iron knows the feeling: the chemistry looks right, the pouring temperature is on target — yet the metallography report shows low nodularity, vermicular graphite or carbides. In many cases, the root cause is not the process itself but the Rare Earth Si-Mg Nodulizer grade that was chosen for it.
This guide explains what this alloy is, what each element does, and how to select the right grade, particle size and addition rate for your production conditions.
What Is a Rare Earth Si-Mg Nodulizer?
A Rare Earth Si-Mg Nodulizer — also called Rare Earth Ferro Silicon Magnesium (FeSiMg RE) or RE-Mg-FeSi — is a ferrosilicon-based master alloy containing magnesium, rare earth elements (mainly cerium and lanthanum), and calcium. It is added to molten iron just before pouring to change graphite from flakes (grey iron) into spheres (ductile iron, also known as nodular or SG iron).
Why not add pure magnesium? Magnesium boils at about 1,090 °C, far below the treatment temperature of molten iron (typically 1,450–1,550 °C). Pure Mg would vaporise violently, with very low recovery and serious safety risks. Diluting Mg in a ferrosilicon carrier makes the reaction controllable, safer and far more efficient.
The Role of Each Element in Rare Earth Si-Mg Nodulizer
| Element | Typical Range | Main Function |
| Mg | 5–10% | The primary nodularizing element. Desulphurises and deoxidises the melt, then promotes spheroidal graphite. |
| RE (Ce, La) | 0.5–8% | Neutralises "anti-nodularizing" tramp elements (Pb, Bi, Sb, Ti, As), strengthens desulphurisation, reduces Mg fade and helps control shrinkage. |
| Si | ≥44% | Carrier for Mg; adds graphitising effect and reduces chill tendency. |
| Ca | 2–5% | Moderates the Mg reaction, reduces flare and smoke, and improves Mg recovery. |
| Al | ≤1% | Kept low to avoid pinholes and subsurface gas defects. |
| MgO | Low as possible | Oxidised magnesium has no nodularizing effect and causes slag and dross. |
In short: magnesium does the work, rare earth provides the insurance. The grade name reflects this — for example, FeSiMg3-8 means about 3% RE and 8% Mg.
Rare Earth Si-Mg Nodulizer Grades from LSFerroalloy
| Grade | RE | Mg | Si | Ca | Al |
| FeSiMg1-6 | 0.5–2.0% | 5–7% | 44% min | 2.0–3.0% | 1% max |
| FeSiMg2-7 | 1.0–3.0% | 6–8% | 44% min | 2.0–3.5% | 1% max |
| FeSiMg3-8 | 2.0–4.0% | 7–9% | 44% min | 3.5–4.0% | 1% max |
| FeSiMg5-8 | 4.0–6.0% | 7–9% | 44% min | 4.0–5.0% | 1% max |
| FeSiMg7-9 | 6.0–8.0% | 8–10% | 44% min | 4.0–5.0% | 1% max |
For full specifications and the third-party test report, see our FeSiMg Nodulizer product page.
Sizes: 5–15 mm, 3–25 mm, 8–40 mm, 25–50 mm, or customised on request. Customised RE/Mg/Ca ratios, low-Al and Ba-containing grades are available.
How to Choose the Right Rare Earth Si-Mg Nodulizer Grade
There is no "best" nodulizer — only the grade that best matches your melting furnace, base iron and castings. Consider these four factors:
1. Melting Furnace and Base Iron Sulphur
- Medium-frequency induction furnace, low-sulphur base iron (S ≤ 0.02%): low-Mg, low-RE grades such as FeSiMg1-6 are usually sufficient and help avoid excessive residual Mg.
- Cupola or duplex melting, higher sulphur: higher Mg and RE grades such as FeSiMg3-8 or FeSiMg5-8, because Mg is consumed first by sulphur and oxygen before it can nodularize.
2. Charge Materials and Tramp Elements
If your charge includes a large share of steel scrap or recycled material, trace elements such as Ti, Pb, Sb and Bi may increase. These interfere with graphite spheroidisation. Higher-RE grades neutralise them and protect nodularity. For clean charge (high-purity pig iron), low-RE grades are preferable.
3. Casting Wall Thickness
- Thin-walled castings (automotive parts, pipe fittings): too much RE can increase chill and carbide tendency. Choose low-RE grades combined with good inoculation.
- Heavy-section castings (wind turbine hubs, large housings): slow cooling causes Mg fade and graphite degeneration (chunky graphite). Grades with controlled RE content, often La-rich, help maintain nodularity in thick sections.
4. Treatment Method and Ladle Size
- Sandwich / tundish-cover method: most common; medium sizes (3–25 mm or 5–15 mm) give stable dissolution.
- Large ladles (several tonnes): larger sizes (8–40 mm or 25–50 mm) avoid floating and premature reaction.
- Small ladles or late treatment: finer sizes dissolve quickly and evenly.
Rare Earth Si-Mg Nodulizer Addition Rate and Mg Recovery
The addition rate typically ranges from 1.0% to 1.8% of the treated iron weight, depending on base sulphur, treatment temperature, ladle design and the target residual Mg (commonly 0.035–0.055% for ductile iron).
A simple estimation:
Addition (%) ≈ [0.76 × S(base) + Mg(residual)] ÷ [Mg(alloy) × Recovery]
With a well-designed sandwich ladle, magnesium recovery commonly falls in the 40–60% range. Always confirm the final addition rate through trial heats and spectrometer analysis. For broader ductile iron process references, the American Foundry Society offers technical resources for foundry engineers.
Practical Tips for Better Results
- Keep it dry. Moisture reacts with Mg, increasing MgO and reducing efficiency. Store in a dry warehouse and keep bags sealed until use.
- Control the treatment temperature. Every unnecessary increase in temperature accelerates Mg vaporisation and lowers recovery.
- Cover the alloy. Use steel scrap, ferrosilicon chips or a cover plate in the ladle pocket to delay the reaction.
- Pour fast. Magnesium fades over time; pour within the recommended window (usually 8–12 minutes after treatment).
- Always inoculate. Nodulizing alone is not enough — follow up with an FeSi-based inoculant to increase nodule count and prevent carbides.
- Check particle size consistency. Excess fines (< 1 mm) oxidise easily and react too fast; excess oversized lumps dissolve unevenly.
Common Problems and What to Check
| Problem | Possible Cause | Suggested Action |
| Low nodularity | Insufficient residual Mg, high S, tramp elements | Increase addition or switch to a higher Mg/RE grade |
| Violent reaction, heavy smoke | High Mg grade, high temperature, poor covering | Use a grade with higher Ca, improve covering, reduce temperature |
| Carbides in thin sections | Excessive RE or Mg, weak inoculation | Choose a lower-RE grade and strengthen inoculation |
| Chunky graphite in heavy sections | Mg fade, excessive Ce, slow cooling | Optimise RE type and content, shorten holding time |
| Slag inclusions, dross | High MgO in alloy, oxidised fines | Use low-MgO alloy, remove slag promptly |
Applications of Rare Earth Si-Mg Nodulizer
Rare Earth Si-Mg Nodulizer is used to produce ductile iron for the following industries (learn more in our article on nodulizer in cast iron production):
- Automotive: crankshafts, camshafts, steering knuckles, differential housings, brake calipers
- Pipes and fittings: ductile iron pipes for water and gas networks
- Wind power: hubs, bases and bearing housings
- Machinery: gearboxes, hydraulic valves, pump bodies and compressor parts
- Rail and agriculture: brake components, tractor parts
Why Choose LSFerroalloy
LSFerroalloy (Anyang Lishi Industrial Co., Ltd) has been manufacturing and exporting ferroalloys since 1999. For Rare Earth Si-Mg Nodulizer, we offer:
- Stable chemistry — tight control of Mg, RE and Ca between batches
- Low MgO and Al for cleaner castings
- Accurate sizing with low fines content
- Customised grades matched to your furnace and castings
- Third-party inspection (SGS, BV, etc.) available on request
- Flexible packaging — 25 kg bags, 1 MT jumbo bags, or as required
FAQ
Q: What is the difference between FeSiMg and Rare Earth Si-Mg Nodulizer? A: They are essentially the same product family. "Rare Earth Si-Mg Nodulizer" highlights that the FeSiMg alloy contains rare earth elements, which improve resistance to tramp elements and stabilise nodularization.
Q: Is a higher RE content always better? A: No. Excessive RE can increase chill and carbides in thin sections and may cause chunky graphite in heavy sections. RE should match your charge quality and casting thickness.
Q: Which grade is most commonly used? A: For induction furnace melting with low-sulphur iron, FeSiMg1-6 and FeSiMg2-7 are the most widely used. For cupola iron or poorer charge materials, FeSiMg3-8 and FeSiMg5-8 are common.
Q: What is your minimum order quantity? A: Please contact us — we supply both trial quantities and full container loads.
Looking for a reliable Rare Earth Si-Mg Nodulizer supplier? Tell us your furnace type, base iron sulphur, ladle size and casting type, and our technical team will recommend the most suitable grade and size. Get a quote and free technical consultation →