Short answer: A cast-iron inoculant can be based on ferrosilicon, but that does not make every standard ferrosilicon lot an interchangeable inoculant. The foundry must select a product for its iron grade, addition point and measured casting result. If the purchase request only says “FeSi 75,” clarify whether the material is intended to adjust base-iron silicon or to provide late inoculation before pouring.
Why the names overlap
Elkem describes ferrosilicon-based inoculants as additions made before pouring to promote graphite nucleation and reduce chilling in cast iron. Ferroglobe notes that inoculant formulations and grain-size distributions vary with the point of addition: furnace, ladle, stream or mould. The silicon carrier is therefore only part of the specification. A seller’s general ferrosilicon analysis does not prove performance in the buyer’s particular casting process.
What to put in the purchase request
- Intended job: base-iron silicon adjustment, preconditioning, or final inoculation. These are different decisions.
- Process: gray or ductile iron, addition location, holding time and the foundry’s current practice.
- Material: full element limits and size distribution required by the plant, including any inoculant-specific elements. Do not assume the label “75% Si” covers them.
- Acceptance: a controlled plant trial with the foundry’s usual measures, such as chill tendency, graphite structure and reject rate. Agree on the trial and acceptance criteria before switching.
If a standard FeSi offer is being compared with a named inoculant, request both full specifications and the intended treatment method. A lower price per tonne is not a useful saving if the casting outcome is different. This is a technical selection for the foundry, not a universal substitution rule. For the separate question of changing silicon percentage in an existing FeSi specification, see our FeSi 72 versus FeSi 75 FAQ.
Scope: This article does not claim Xinrui supplies a specialised inoculant or that any particular Xinrui lot has passed a foundry trial. Ask for the exact product and application before ordering.
Sources
- Elkem, What are inoculants?, accessed 29 October 2026.
- Ferroglobe, Foundry Products, accessed 29 October 2026.
