**Bearing Steel Casting and Heat Treatment Process**
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Bearing steel casting is a critical process in the production of high-performance rolling bearings. These bearings must have high compressive strength, fatigue resistance, hardness, and wear resistance. They also need to be resistant to hardening, with extremely strict control over sulfur and phosphorus content. The specific gravity of bearing steel is approximately 7.81.
The casting process involves several key steps, including preheating, forging, and heat treatment. Proper temperature control is essential to avoid defects and ensure the material's structural integrity.
**Casting Temperature Parameters**
- **Initial Forging Temperature:** 1150°C (1120°C)
- **Final Sintering Temperature:** 850°C (800°C)
During the casting process, it's important to preheat the material quickly and avoid entering the brittle zones. Specifically:
- During warm working, avoid the **blue brittle area (200–400°C)**.
- During hot working, avoid the **high-temperature brittle area (>1250°C)** and the **hot fragile area (800–950°C)**.
**Post-Forging Heat Treatment**
After forging, the following heat treatments are typically performed:
1. **Pre-Heat Treatment (Spheroidizing Annealing):** This reduces hardness, improves machinability, and prepares the material for quenching.
- Heating temperature: 750–770°C
- Insulation time: Sufficient to allow full transformation
- Cooling: Air cool below 600°C
2. **Final Heat Treatment (Quenching + Low-Temperature Tempering):**
- Quenching temperatures vary depending on the type of bearing steel.
- Common quenching media include water, oil, or salt/alkali solutions.
- Low-temperature tempering is applied to reduce internal stress while maintaining high hardness and wear resistance.
**Quenching and Tempering Parameters for Different Bearing Steels**
| Bearing Steel | Quenching Temperature (°C) | Quenching Medium | Tempering Temperature (°C) | Hardness (HRC) |
|---------------|-----------------------------|------------------|----------------------------|----------------|
| GCr6 | 800–820 | Water/Oil | 150–170 | 62–64 |
| GCr9 | 800–830 | Water/Oil | 150–170 | 62–64 |
| GCr9SiMn | 810–820 | Water/Oil | 150–160 | 62–64 |
| GCr15 | 820–846 | Oil | 150–160 | 62–64 |
| GCr15SiMn | 800–840 | Oil | 150–170 | 62–64 |
**Quenching Media and Techniques**
- **Water:** Typically used at temperatures below 40°C. It must be clean and free from oil or impurities.
- **Salt or Alkali Solutions:** Adding 5–10% salt or alkali increases cooling rate tenfold compared to water, resulting in higher and more uniform hardness, but with increased internal stress and potential rusting.
- **Oil:** Used for carbon steels to reduce deformation and cracking. Common oils include spindle oil, transformer oil, and diesel. Oil temperature should be between 60–80°C, not exceeding 100–120°C.
**Tempering Process**
Low-temperature tempering is preferred for bearing steel, typically at 150–250°C. This helps maintain high hardness and wear resistance while reducing brittleness and internal stress. The final hardness after tempering usually ranges from HRC 58 to 64.
**Conclusion**
Proper casting and heat treatment are essential for producing high-quality bearing steel that meets the demanding requirements of modern machinery. By following precise temperature controls and appropriate heat treatment methods, manufacturers can ensure the durability, performance, and reliability of their bearings.
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Bearing Steel Casting
Source: Bearing Network | Time: 2014-01-06
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