Dear Fabrice Kapiamba the crystal structure of the carbide Cr23C6 has been reported already in 1972 in a paper published in the journal Acta Crystallographica B. The article is available as full text free of charge (see attached).

You can use EDD analysis if the particles are large. Otherwise, you may need to use SAD pattern and TEM base studies for submicron and nano sized ones.

Depending on chemical composition and microsegregation in steel, it is possible to observe NbC, Nb(C, N) precipitates with 5-10 micron. If you want to distinguish precipitates in these sizes, it is possible to use SEM EDX. Otherwise you need a TEM analysis for nanoscaled ones as Mr. Saman said.