Improving Cleanliness and Controlling Inclusion Characteristics in High-Nitrogen Stainless Bearing Steels by Optimizing Addition Order and Contents of Mg and Ce

The cleanliness and inclusion characteristics are crucial to the service life of bearing steels. In this work, the effects of addition order and contents of Mg and Ce on cleanliness and inclusion characteristics in high-nitrogen stainless bearing steels were systematically investigated by microstructure characterization and thermodynamic analysis. The results showed that the O and S contents could be decreased from about 0.0040 wt pct and 0.0028 wt pct to 0.0012 wt pct and 0.0014 wt pct, respectively. The inclusion evolution processes by Mg pretreatment and Ce addition (MgCe) were: Al 2 O 3 → MgO and MnS → MgS + Ce–O–S, and those of Ce pretreatment and Mg addition (CeMg) were: Al 2 O 3 → Ce–O–S and MnS → Ce–O–S + MgS, which were consistent with thermodynamic calculation. For MgCe treatment, owing to the high Ce content (0.018 wt pct), the number density ( N A ), total area ( S ) and average size ( d ) of inclusions were large, and those would decreased by reducing the Ce content to 0.012 wt pct. For CeMg treatment, a large number of Mg-containing inclusions (especially deleterious Mg 3 N 2 ) formed because of the high Mg content (0.0066 wt pct). As the Mg content decreased to 0.0043 wt pct, the N A and S of inclusions increased instead. In this study, the optimum addition order was Mg pretreatment and Ce addition, and the optimized contents were about 0.0044 wt pct and 0.012 wt pct, respectively.