Research on inclusion control in GCr15 bearing steel based on Al-Si complex deoxidation

In the conventional Al deoxidation process of GCr15 bearing steel, large-sized Ds type inclusions are prone to form, which will have a significant impact on its fatigue life. In order to reduce the hazards caused by such inclusions, the development of non-fully Al-deoxidation processes has become the direction for the advancement of bearing steel. This study conducted a systematic investigation on the Al-Si composite deoxidation process adopted by a certain steel plant. Through systematic sampling throughout the process and calculation using thermodynamic software, it was found that the type of inclusions changed from spinel to inclusions mainly consisting of 1–3 µm Al 2 O 3 -SiO 2 composite oxides. The research results show that in the initial stage of the RH vacuum process, the high vacuum environment promotes the decomposition of CaO-SiO 2 , resulting in a slight increase in [Ca] content. After the RH venting, under normal pressure conditions, [Ca] will preferentially react with [O], causing a temporary decrease in [Ca] content. In the tundish stage, due to the decrease in molten steel temperature and the increase in MgO content, the original liquid inclusions transform into high-melting-point solid inclusions. The transformation of liquid inclusions into solid form helps them rise and be removed from the molten steel. Therefore, the density of inclusions decreased from 13.98 N/mm −2 before RH vacuum treatment to 3.47 N/mm −2 after RH vacuum treatment. These findings indicate that the Al-Si deoxidation route is effective for controlling the number of large-sized inclusions and improving the purity of GCr15 bearing steel.