Effects of refining slag basicity and vacuum treatment on the cleanliness of bearing steel

The effect of vacuum treatment on the cleanliness of low Ti steel treated with low basicity refining slag was studied by analyzing the change of oxygen content and inclusions characteristics in the steel after the interaction between different basicity slags and GCr15 bearing steels and after vacuum treatment. The results show that the oxide inclusions in the steel are mainly MgO·Al2O3 after slag-steel interaction. The low basicity slag refining is beneficial for decreasing the harm of TiN inclusions due to the better low Ti content control. However, the oxygen content and the number of inclusions in the steel increase with the decrease of slag basicity (CaO/SiO2 mass ratio), which means that the decrease in the basicity is disadvantageous to the cleanliness of steel. Typical inclusions in the steel transform into smaller MgO inclusions and MgS–MgO-(MnS) composite inclusions after vacuum treatment, and the oxygen content of steel is decreased to the same level. Furthermore, the size and number density of inclusions are significantly decreased after the vacuum treatment. It indicates that the combined process of low basicity slag refining and vacuum carbon deoxidation can realize the TiN inclusion control and cleanliness improvement of GCr15 bearing steel.