Summarizing inclusion identification techniques can be divided into two categories. The first category is the in-position identification inspection. In-place identification inspection is performed under the condition that the inclusions and the steel matrix are not separated. It can be divided into macro-in-place inspection and micro-in-place inspection. Macro on-site inspections include: low-power acid immersion, sulfur printing, X-ray transmission, and ultrasonic inspections. These methods can determine the location, size and distribution of inclusions (or defects) in the steel or workpiece. According to the results of these inspections, the influence of process factors on the cleanliness of steel can be evaluated, and inclusion defects that are difficult to be found by the naked eye can be found, so as to avoid continuing processing or putting into use, causing undue damage and loss. However, the macroscopic on-site inspection often cannot determine the type and composition of inclusions. The micro-in-place inspection makes up for this deficiency.