Inoculants (Ca-Ba, Sr, Zr based FeSi)

Inoculants are added to molten cast iron shortly before pouring to increase the number of graphite nucleation sites. This reduces white iron (chill) formation, improves graphite distribution and gives a machinable structure even in thin sections. In ductile iron they increase nodule count and favour a ferritic matrix.

Types: Ca-Ba based FeSi inoculants are widely used in grey and ductile iron and resist fading better. Sr based inoculants are used at low addition rates, mainly for chill control in grey iron. Zr based inoculants are preferred in high-silicon and thin-section grey iron. The choice depends on the base iron sulphur level, casting section and pouring temperature.

The inoculation effect fades over time, so the addition is made as close to pouring as practical: in the ladle, in the stream or in the mould (in-mould). Grain size is chosen according to the addition method; very fine grain can cause dust loss and sticking to the ladle wall.