Before becoming a freelance translator I worked as the supervisor of the NDT department in a light alloys foundry. When carrying out radiographic interpretation, we just referred to these as oxide inclusions.
I can't remember using a grading scale. The specifications we used allowed oxides up to a certain size and/or a certain number of oxides per /area or volume.
I would be tempted to use point-type and level, although I am not certain about these two terms. (Point-type seems to contrast well with linear inclusions, ref your other query.)
The reference below refers to a rating scale for inclusions.