When high-carbon chromium bearing steel (such as GCr15, containing about 1% carbon) is quenched and heated, the carbon potential in the furnace must match the carbon content of the material: a low carbon potential will lead to decarburization, while a high carbon potential will lead to surface carburization and increased retained austenite. Bearing rings and rolling elements have strict requirements on hardness, structure, retained austenite and dimensional stability, requiring a stable protective atmosphere, accurate carbon potential control, precise quenching and tempering (cold treatment if necessary). Carburized bearing steel is also used for large and heavy-duty bearings.
- GCr15 contains about 1% carbon, and the heating before quenching carbon potential should match it.
- Low carbon potential → decarburization; high carbon potential → carbonization and paralysis increase
- Quality concerns: hardness, structure, retained austenite, dimensional stability
- Mesh belt furnaces and roller hearth furnaces are often used for ferrules and rolling elements.
- Carburized bearing steel is used for heavy-duty, large bearings
Bearing materials and heat treatment routes
| Material type | Represent | Heat treatment route |
|---|---|---|
| High carbon chromium bearing steel | GCr15、GCr15SiMn | Spheroidizing annealing → quenching → tempering (cold treatment if necessary) |
| Carburized bearing steel | Such as G20CrNi2Mo, etc. | Carburizing → Quenching → Tempering |
| other | Stainless bearing steel, high temperature bearing steel | Specialized process according to material |
Carbon potential matching in heating before quenching
GCr15 contains about 1% carbon and is a high carbon steel. When quenching and heating:
- Carbon potential is low: Surface decarburization, insufficient hardness, and contact fatigue life is significantly reduced;
- Carbon potential is high: Surface carburization, residual austenite increases, dimensional stability becomes worse, and even surface carbide abnormalities occur.
Therefore, the carbon potential needs to be set at a level close to the carbon content of the material (taking into account alloy factor correction) and controlled stably. In continuous furnaces such as mesh belt furnaces and roller hearth furnaces, the carbon potential of each zone and the air infiltration at the entrance and exit need to be paid attention to.
Critical quality characteristics
- hardness: The ferrules and rolling elements have strict hardness ranges;
- Microstructure: Martensite, carbide distribution, no troostite, etc.;
- retained austenite: Affects dimensional stability, precision bearings are often controlled by cold treatment and tempering;
- decarburization layer: Usually required to be very shallow or completely removed in subsequent grinding;
- Dimensional stability: Tempering temperature and time should be sufficient.
Key points of process control
- Stable protective atmosphere: endothermic gas or strictly controlled nitrogen-based atmosphere;
- Oxygen probe closed loop + daily calibration;
- Quenching medium temperature and cooling characteristics detection;
- Temperature uniformity of tempering furnace;
- Complete traceability records.
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Frequently asked questions
Why does bearing quenching require the carbon potential to be so accurate?
High carbon steel is sensitive to changes in surface carbon. Slight decarburization or carburization will affect hardness, retained austenite and fatigue life, while the life of bearings is extremely sensitive to surface quality.
Is cold treatment necessary?
Not required for all bearings. In precision bearings or when high dimensional stability requirements are required, cold treatment is often used to reduce retained austenite.
What should I do if the outlet parts of the mesh belt furnace are inconsistent in color?
Check the exit flame curtain, cooling section seal and air flow distribution. Color differences often indicate local oxidation or uneven atmosphere.