This study aims to clarify the behavior of inclusions containing CaO, the inclusions which can adversely affect the fatigue life of bearing steel. Focus was placed on the behavior of the CaO containing inclusions during ladle furnace(LF) treatment. A tracer element was added to the top slag prior to the LF treatment to identify the origin of the inclusions. As a result, the main origin of the CaO element in the inclusions is LF top slag entrapped during gas stirring, and this is confirmed by the formation kinetics of the inclusions. The quality of ultrafine bearing steel was improved by applying countermeasures to suppress slag entrapment.
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