Inoculants are vital additives in cast iron production, enhancing graphite morphology, refining microstructure, and boosting mechanical properties.
1. Main Types of Inoculants
Silicon-Calcium Inoculant (SiCa)
Features: 1.5–2 times stronger graphitization ability than 75FeSi. Calcium (Ca) reacts with O, S, N, and H in molten iron, cleaning impurities and forming graphite nucleation sites. Contains 2.4% Al, further boosting the inoculation effect.
Drawbacks: Fast fading, more slag, low density, and higher pollution. Low-calcium grades (<16% Ca) help reduce these issues.
Applications: Gray and ductile cast iron requiring high graphite quality.
Stream Inoculant (In-stream Feeding)
Definition: Inoculant is crushed to 0.2–0.8 mm and fed into molten iron during pouring.
Advantages: Precise dosage, high efficiency, reduced fading, and suitable for large-scale production.
Silicon-Barium Inoculant (SiBa)
Features: Strong graphite promotion, finer graphite, improves A-type graphite in gray iron and nodularity in ductile iron. Strong anti-fading ability, reduces white iron tendency, improves machinability.
Particle sizes:
0–0.25 mm: In-mold inoculation.
0.2–1 mm: Stream inoculation.
1–3 mm, 3–8 mm: Ladle inoculation (≥70% of tapping time).
8–15 mm: Furnace inoculation.
Dosage: 0.3–0.6%. Excessive use increases slag, shrinkage risk.
Ferrosilicon Grain Inoculant (FeSi)
Features: Cost-effective, widely used as both inoculant and nodulizer. Reduces white iron, promotes A-type graphite, improves strength and toughness. 75FeSi is most common.
Key role of Al and Ca: Form high-melting compounds that act as graphite nucleation sites.
Strontium-bearing Ferrosilicon (Sr-FeSi)
Features: Strong ability to eliminate white iron, ideal for thin-wall castings, improves graphite uniformity, and reduces structural differences.
Barium-bearing Ferrosilicon (Ba-FeSi)
Features: Enhances graphite formation, slows fading, requires lower addition than 75FeSi.
Zirconium-bearing Ferrosilicon (Zr-FeSi)
Features: Acts as a deoxidizer, improves fluidity, reduces white iron tendency, refines A-type graphite, and delays fading.
Rare Earth Inoculants
Types: Rare earth mixed metals, rare earth ferrosilicon.
Features: Much stronger than 75FeSi, effectively eliminates white iron and resists fading.
Carbonaceous Inoculants
Application: Used as pre-treatment before inoculation. Materials include SiC (85–90%) and crystalline graphite.
2. Key Steps for Inoculant Application
Determine dosage: Proper addition is critical. Too little, weak effect. Too much, high viscosity, slag, shrinkage, and performance loss.
Choose method:
Ladle inoculation: Add to the ladle, molten iron flush ensures mixing.
Stream inoculation: Small particles added with molten iron flow, instant and precise.
In-mold inoculation: Inoculant blocks are placed in the mold for special castings.
Control reaction speed: Avoid too fast or too slow reactions. Adjust temperature, stirring, and timing.
Ensure uniform distribution: Prevent local defects by thorough mixing.
Avoid over-inoculation: Prevent viscosity increase, slag, and shrinkage. Use testing (metallography, hardness) for optimization.
Safety: Many inoculants contain reactive elements (Ca, Ba). Operators must be trained, wear PPE, and follow safety protocols.
3. Summary
The choice of inoculant depends on cast iron type, wall thickness, and performance requirements. SiCa offers high efficiency, SiBa provides strong anti-fading ability, FeSi is cost-effective, while rare earth inoculants deliver superior results. Controlled dosage and proper methods are key to stable casting quality.
4. LSFerroalloy Advantages
Technical Precision: Tailored inoculant solutions for different cast iron types, improving graphite morphology and fading resistance.
Stable Quality: Strict control of particle size and purity, ensuring reliable reaction and uniform distribution.
Service & Support: Professional, technical, and sales team, third-party testing, and timely solutions.
At LSFerroalloy, our principle is “Technology as foundation, Quality as core”. We not only supply reliable inoculants and ferroalloys, but also strive to be a trusted partner in casting solutions.