An inclusion is a particle, greater than ~0.5µm in size and is generally found in all steels, even the very purest of steels.  The most common inclusions found in steel are oxides and sulphides; these species can be quite simple in nature containing just one component (e.g. alumina particles Al₂O₃) but very often come from much more complex multi-component systems such as the inclusions from a weld metal shown in the micrograph.

Other inclusion species found in steel include large nitrides, carbo-nitrides and lead inclusions. 

In addition to chemistry, inclusions are characterised by their size and shape (also called 'morphology' and which is largely determined by inclusion chemistry); inclusions can be angular, globular or highly elongated.

Identify the following inclusions using the energy dispersive X-ray (EDX) analysis. Position the probe onto the inclusion and use the resulting EDX trace to identify the chemistry of the inclusion - watch out as some of the inclusions may have more than one constituent.