Study on the modification of inclusions by Ca treatment in GCr18Mo bearing steel

Abstract

The effect of Ca treatment on the modification of inclusions in Al-killed GCr18Mo bearing steel was studied and a thermodynamic and kinetic model was established. The experimental results showed that oxygen content in the steel could be reduced from 120 μg/g to the range 5.5–21.6 μg/g by Al-Ca complex deoxidization at 1 873 K. An appropriate increase in Ca/Al mass ratio is beneficial to reduce the total oxygen content in steel. When the content of dissolved aluminum was in the range of 0.03%–0.3%, with the increase of Ca/Al mass ratio from 0.8–1.6 to 2.4–3.2, the number of inclusions per unit area significantly reduced. In addition, the main types of inclusions were modified from large-sized Al₂O₃ clusters to plastic or semi-plastic liquid phase calcium aluminates. The experimental results matched well with the thermodynamic analysis.

Keywords

GCr18Mo bearing steel / Ca treatment / Inclusion modification / Deoxidization / Thermodynamics

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Funding

Joint Fund of Iron and Steel Research http://dx.doi.org/10.13039/501100010900(U1560202)