Inoculant

 

Inoculant can promote graphitization, reduce whitening tendency, improve graphite morphology and distribution, increase the number of eutectic clusters and refine matrix structure. It has good effect in a short time (about 5-8 minutes) after inoculation. It is mainly applicable to general elements or instantaneous incubation in later stage in various situations. Inoculation treatment refers to the addition of a small amount of other substances to the liquid metal during solidification process to promote nucleation, inhibit growth and achieve the purpose of grain refinement. Traditionally, adding additives to cast iron is called inoculation treatment, and adding additives to non-ferrous alloys is called modification treatment. In essence, inoculation treatment mainly affects nucleation and promotes grain dissociation, while modification treatment changes the growth mechanism (inhibiting growth) of crystals, thereby affecting the morphology of crystals.

 

Brand name	Main Components					Scope of application
	Si	Ba	Ca	Al	Other
DR Ba-1	65-75	-	0.5-2.5	≤2.5	allowance	It is suitable for grey casting and inoculation treatment of nodular cast iron to refine graphite and reduce whiteness.
DR Ba-2	65-75	4-6	0.5-2.5	≤2.5	allowance	It is suitable for grey casting and inoculation treatment of nodular cast iron to refine graphite and reduce whiteness.
DR Ba-3	55-65	4-6	0.1-0.5	≤0.5	allowance	It is suitable for inoculation treatment of gray cast iron or ductile iron with strict requirements for air tightness or leakage.
DR Ba-4	50-60	12-20	0.5-2.5	≤2.5	allowance	It is suitable for inoculation treatment of nodular iron castings with long holding time and long casting time in molten iron.

 

 

 

 

 

 

 

 

 

Background
A Czech foundry producing turbocharger housings and exhaust manifolds (wall thicknesses: 3–8 mm) struggled with two critical defects: primary carbides at corners and micro-shrinkage in heavy bosses. Their standard 75% ferrosilicon inoculant (0.75–1.0% addition) failed to provide sufficient nucleation sites, resulting in a 15% scrap rate and rejected shipments to an OEM customer.

 

The Challenge
The foundry needed an inoculant capable of:

Eliminating chill and carbides in sections under 4 mm

Providing 15+ minutes of fade resistance for large pouring ladles

Reducing shrinkage tendency without changing gating design

Maintaining consistent nodule counts (target: >250/mm²)

 

Solution
They switched to a high-efficiency proprietary inoculant with the following composition:

Active elements: Si 70–73%, Ca 1.5–2.0%, Al 0.75–1.0%, Sr 0.6–1.0%, RE (La/Ce) 0.3–0.5%

Grain size: 0.2–0.8 mm (for late-stream inoculation)

Key feature: Strontium addition to suppress carbides without increasing shrinkage

Implementation Process
The new inoculant was applied using a two-step method:

Step	Method	Addition Rate	Temperature
1	Ladle inoculation (sandwich)	0.4%	1,480°C
2	Late-stream (pouring stream)	0.15%	1,390–1,420°C

Holding time from inoculation to solidification was maintained under 12 minutes.

 

Results (After 120 Production Heats)

Parameter	Standard Inoculant	Premium Inoculant	Improvement
Carbide area (%)	8–12%	<1%	-88%
Nodule count (/mm²)	180	310	+72%
Shrinkage porosity (vol%)	2.8%	0.6%	-79%
Chill depth (mm)	2.5	0.3	-88%
Tensile strength (MPa)	410 ± 35	485 ± 12	+18% (less scatter)
Scrap rate	14.7%	2.1%	-86%

 

Key Observations

Carbide-free corners: Even at 3 mm wall thickness, the Sr-modified inoculant promoted graphite nucleation within 30 seconds of solidification.

Fade resistance: Nodule count remained above 220/mm² after 14 minutes, compared to 120/mm² with standard inoculant.

Reduced dross: Lower aluminum content (0.8% vs. 1.5% in standard grade) cut pinhole defects by 70%.

Improved machinability: Consistent ferritic matrix eliminated tool breakage during drilling operations.

Financial Impact
The foundry achieved annual savings of €210,000:

€95,000 from reduced scrap and rework

€65,000 from lower magnesium addition (better nucleation allowed 0.05% less Mg)

€50,000 from extended tool life in machining

 

Conclusion
By adopting a premium Sr/RE-bearing inoculant with controlled grain size and late-stream application, the foundry successfully produced thin-wall ductile iron (EN-GJS-450-10) with zero carbides and minimal shrinkage. The customer approved re-qualification within six weeks.

 

Recommendation
For thin-wall castings (<6 mm) or heavy-section mixed castings, choose an inoculant with:

Strontium or bismuth for carbide suppression

Rare earths for nodule count stability

Fine grain size (0.2–0.8 mm) for late-stream use

Verified fade curve (retain >50% effectiveness at 15 minutes)

Premium inoculant costs €30–50 more per ton of metal but typically pays back within 3 shifts through scrap reduction alone.

 

📧E-mail: goldenltd.silicon@gmail.com                 📞WhatsApp: 86 16663721147

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