Effect of Mg Treatment on the Evolution of Inclusions in M50 Aerospace Bearing Steel Under Different S/O Ratio Conditions

Herein, laboratory experiments and thermodynamic calculations are conducted to study the influence of Mg treatment on the inclusion behavior of M50 aerospace bearing steels under different S/O mass ratios (mass ratios of S content to O content). The type, morphology, and distribution of inclusions in ingots with and without Mg treatment are characterized by the scanning electron microscope, energy‐dispersive X‐Ray spectroscopy, and ASPEX automated inclusions analysis system. In addition, the phase distributions of inclusions in M50 steels are simulated using FactSage software to clarify the mechanism of inclusion evolution during the smelting and solidification processes. For both high and low S/O mass ratio steels, the primary spinel and Al 2 O 3 inclusions can be completely modified into MgO inclusions and MnS can be partially transformed into MgS inclusions by Mg treatment. After Mg treatment, the size and number density of inclusions show a noticeable increase in high S/O mass ratio steel resulted from a mass of MgS formation but a slight decrease in low S/O mass ratio steel due to the MgO removal by floatation. Based on the present study, an optimal S/O mass ratio for tight control of detrimental inclusions in Mg‐treated M50 steels is obtained.