Genesis of inclusions
Non-metallic inclusions in steel

Inclusions can form before or during solidification; some appear in solid metal. When they are formed from the usual elements of steel, they are called endogenous inclusions. If chemical compounds are brought in from outside, in the case of accidental pollution, they are called exogenous inclusions; the latter react at least in part with the metal to give mixed inclusions.

The times and locations of inclusion formation are shown in figure 7 .