Abstract: Taking high carbon chromium bearing steel as the research object, the reasons for the failure of flaw detection of bearing steel were analyzed through SEM and Feature inclusions automatic analysis system. Different inclusions that caused the failure of flaw detection were classified and statistically analyzed. The results showed that the inclusions causing the failure of flaw detection were mainly MgO-Al₂O₃ and CaO-Al₂O₃ semi-liquid inclusions, accounting for 42.31% and 38.46%, respectively. The evolution and formation mechanism of inclusions with a size not less than 3 μm in the whole process of LF-RH-CC were analyzed through industrial tests, and the results showed that MgO-Al₂O₃ inclusions continued to increase in the LF refining process, and the size of inclusions in the steel increased at the late stage of LF refining, but the index of MgO-Al₂O₃ and Al₂O₃ decreased rapidly to about 0 after RH refining. Until the secondary oxidation caused mass formation of MgO-Al₂O₃  in the tundish while the casting process. The aggregation, growth, and inheritance of MgO-Al₂O₃  have become a primary cause of immersion ultrasonic testing failures. Therefore, in order to reduce the MgO-Al₂O₃  and CaO-Al₂O₃ semi-liquid inclusions in the steel, it is recommended that in the actual smelting process, control the appropriate LF refining and RH refining soft blowing time，reduce the calcium content of the raw materials, and strictly control the casting process to reduce the degree of secondary oxidation.

Key words: bearing steel, the failure of flaw detection, inclusions, evolution law