**Control of Brittle Inclusions in GCr15 Bearing Steel**
Home > Bearing Knowledge > Control of Brittle Inclusions in GCr15 Bearing Steel
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*Source: China Bearing Network | Date: March 10, 2014*
Brittle inclusions in GCr15 bearing steel can significantly reduce the fatigue life and mechanical properties of the material, ultimately affecting the overall quality of the steel. Microscopically, GCr15 steel contains various types of non-metallic inclusions, such as D-type inclusions (O-Al-Ca-S), O-Al-Mg-Ca-(S), and Ti-N-Cr. These inclusions are often associated with the slag system, refractory materials, and vacuum treatment process.
To effectively control these brittle inclusions, several key strategies should be implemented:
1. **Optimization of the Slag System**
Selecting an appropriate slag composition is crucial for minimizing inclusions. A suitable slag system could be CaO (40–60%) – Al₂O₃ (20–40%) – SiO₂ (4–10%) – MgO (5–12%). High-alkalinity slags (CaO/SiO₂ > 3) are typically preferred for their ability to reduce the final steel's impurity content and improve slag fluidity. This allows better removal of non-metallic inclusions, leading to a more stable and low-brittleness steel.
2. **Selection of Refractory Materials**
During the melting process, the steel reaches temperatures up to 1600°C, which can cause severe corrosion of the ladle, tundish, and nozzles. For high-alkalinity operations, refractories with high magnesium oxide content are recommended. For low-alkalinity conditions, chromium oxide or high-alumina materials are more suitable. Additionally, zirconia-containing materials are used for continuous casting nozzles to enhance durability.
3. **Vacuum Treatment and Argon Blowing**
Under VD (Vacuum Degassing) conditions, extending the argon stirring time helps ensure complete reaction between the slag and molten steel, allowing inclusions to float out more efficiently. However, it’s important to balance the intensity of argon blowing to avoid damaging refractory materials or introducing oxygen into the melt. Proper control ensures that inclusions are removed without causing contamination.
In addition, maintaining a low total oxygen level in the steel ([O] ≤ 8 × 10â»â¶) is essential for improving the purity of the molten steel. In July 2007, Xingcheng Special Steel successfully applied these methods to achieve better control over brittle inclusions in GCr15 bearing steel, meeting production requirements effectively.
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