Non-metallic inclusions

The cleanliness of alloys is, in the main, defined in terms of non-metallic inclusions. Improved properties of castings result from reducing the number of inclusions. Inclusions are introduced during every stage of processing, from melting, trimming additions, deoxidation, tapping and teeming, as well as being generated within the mould itself. Inclusions are generally termed:

Exogenous – which arise from external sources and are typically particles of sand, refractory, moulding materials, melting and ladle slags and agglomerates of any of these.
Indigenous – which originate from chemical reaction between elements within the melt itself during melting and deoxidation, and reoxidation, which occurs
during tapping and teeming. Such inclusions are essentially silicates, oxides, nitrides and sulphides, or more often complexes of these.

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