What Is High-Temperature Bearing Steel?
High-temperature bearing steel is a special type of bearing steel designed for rolling bearings that operate under elevated temperatures. When the working temperature of a bearing exceeds 250°C, ordinary bearing steel may lose hardness, dimensional stability, and fatigue strength. In applications such as aero engines, gas turbines, nuclear reactor systems, and X-ray tube tungsten discs, bearing operating temperatures can reach 300°C to 600°C. In these conditions, high-temperature bearing steel is required.
In addition to the basic properties required for conventional bearing steel, high-temperature bearing steel must also maintain reliable performance under heat. Typical requirements include high-temperature hardness, wear resistance, contact fatigue strength, oxidation resistance, impact resistance, and dimensional stability.
Key Performance Requirements of High-Temperature Bearing Steel
- High-temperature hardness: The steel should retain a hardness above approximately 50 HRC at elevated temperatures.
- High-temperature wear resistance: The material must resist wear under continuous rolling contact and high-speed operation.
- High-temperature contact fatigue strength: The steel must withstand repeated contact stress without premature fatigue failure.
- Oxidation resistance: The bearing surface should remain stable in high-temperature oxidizing atmospheres or corrosive environments.
- High-temperature impact resistance: The steel should resist cracking or damage caused by impact loads at elevated temperatures.
- Dimensional stability: The bearing must maintain its fit, clearance, and geometry during temperature changes.
Common Types of High-Temperature Bearing Steel
Cr4Mo4V High-Speed Steel
Cr4Mo4V is a molybdenum-containing high-speed steel. It offers good dimensional stability, high-temperature hardness, and high-temperature contact fatigue strength. However, its forging and machinability are relatively poor, and it is sensitive to decarburization during heat treatment. Cr4Mo4V is commonly used to manufacture bearing rings and rollers for rolling bearings operating at high temperatures.
Cr14Mo4 High-Temperature Stainless Bearing Steel
Cr14Mo4 is a high-temperature stainless bearing steel with high-temperature hardness and good corrosion resistance. Its high-temperature contact fatigue strength is slightly lower than that of Cr4Mo4V, but its machinability is better. It is suitable for components operating under medium or low loads at temperatures below 300°C.
W18Cr4V Tungsten High-Speed Steel
W18Cr4V is a tungsten-based high-speed steel with high hot hardness and excellent red hardness. It is widely used for cutting tools and can also be used for high-temperature bearing components operating below approximately 540°C.
W9Cr4V2Mo High-Speed Steel
W9Cr4V2Mo has performance characteristics similar to Cr4Mo4V. However, its hot workability and grinding performance are relatively poor. It is suitable for manufacturing high-temperature bearings that operate continuously below 400°C.
W6Mo5Cr4V2 Tungsten-Molybdenum High-Speed Steel
W6Mo5Cr4V2 is a tungsten-molybdenum high-speed steel. Compared with W18Cr4V, it has better toughness, wear resistance, and hot plasticity, while maintaining similar hardness, red hardness, and high-temperature hardness. It also has good hot working and machining performance. This steel is suitable for cutting tools, wear-resistant cold extrusion dies, high-temperature springs, and high-temperature bearings.
Why These Steels Can Work at High Temperatures
High-temperature bearing steels usually contain alloying elements such as tungsten (W), molybdenum (Mo), chromium (Cr), and vanadium (V). These elements form carbides that are difficult to dissolve at high temperatures. During tempering, finely dispersed carbides precipitate within the steel matrix, creating a secondary hardening effect.
Because of this strengthening mechanism, high-temperature bearing steels can maintain higher hardness, better wear resistance, stronger oxidation resistance, improved fatigue performance, and better dimensional stability within a certain temperature range.
Working Temperature of Common High-Temperature Bearing Steels
| Steel Grade | Maximum Working Temperature | Temperature for Hardness Test | Hardness at Temperature | Dimensional Stability Time | Allowed Dimensional Change | Oxidation Resistance |
|---|---|---|---|---|---|---|
| Cr4Mo4V | 315°C / 425°C* | 20°C | >62 HRC | 1200 h | <0.005% | Good |
| 230°C | >59 HRC | |||||
| 315°C | >57 HRC | |||||
| 425°C | >54 HRC | |||||
| W6Mo5Cr4V2 | 425°C | 20°C | >62 HRC | 1200 h | <0.005% | Good |
| 230°C | >61 HRC | |||||
| 315°C | >60 HRC | |||||
| 425°C | >57 HRC | |||||
| W9Cr4V2Mo / W18Cr4V | 480°C | 20°C | >63 HRC | 1200 h | <0.005% | Good |
| 200°C | >61 HRC | |||||
| 315°C | >60 HRC | |||||
| 425°C | >57 HRC | |||||
| 535°C | >54 HRC | |||||
| Cr15Mo4 / Cr14Mo4 | 315°C / 425°C* | 20°C | >63 HRC | 1200 h | <0.005% | Excellent |
| 320°C | >57 HRC | |||||
| 420°C | >54 HRC |
*Note: The temperature shown in brackets refers to the maximum allowable temperature under specific conditions.
Material Selection Above 500°C
When the bearing operating temperature exceeds 500°C, high-temperature bearing steel may no longer meet the required performance level. In such extreme conditions, materials such as cobalt-based alloys, nickel-based alloys, or ceramic materials are usually recommended for better high-temperature strength, oxidation resistance, and service life.
Summary
High-temperature bearing steel is used when conventional bearing steel cannot withstand the required operating temperature. Grades such as Cr4Mo4V, Cr14Mo4, W18Cr4V, W9Cr4V2Mo, and W6Mo5Cr4V2 are selected according to temperature, load, corrosion resistance, machinability, and dimensional stability requirements. For applications above 500°C, cobalt-based alloys, nickel-based alloys, or ceramic bearing materials should be considered.
