Rolling Bearing Steel: Performance Requirements and Failure Mechanisms

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Introduction

Rolling bearings operate under extremely demanding conditions. During service, bearing components are subjected to complex stress states such as tension, compression, bending, shear, and high-frequency alternating loads. In many applications, bearings must operate continuously at high speed and under high contact stress for long periods of time.

Therefore, the selection of bearing steel plays a decisive role in determining bearing performance, reliability, and service life. In practice, the basic principle of material selection is closely related to the failure mechanisms of rolling bearings.

Main Failure Modes of Rolling Bearings

The most common failure modes of rolling bearings include:

Contact fatigue flaking under cyclic stress
Loss of precision caused by wear and friction
Abnormal failures such as cracks, dents, corrosion, and surface damage

Among these, contact fatigue failure is the dominant mode. As a result, rolling bearing steel must exhibit a well-balanced combination of mechanical strength, wear resistance, and structural stability.

1. High Contact Fatigue Strength

During operation, rolling elements repeatedly contact the raceways of the inner and outer rings. The contact zone experiences extremely high cyclic stresses, often reaching tens or even hundreds of thousands of load cycles per minute.

Under repeated alternating stress, fatigue cracks initiate below the surface and eventually develop into surface flaking. Once flaking occurs, bearing vibration, noise, and operating temperature increase rapidly, leading to premature failure.

For this reason, rolling bearing steel must possess high contact fatigue strength to ensure long service life under continuous cyclic loading.

2. High Wear Resistance

Although rolling motion dominates bearing operation, sliding friction inevitably occurs at several locations, including:

Contact surfaces between rolling elements and raceways
Contact between rolling elements and cage pockets
Contact between cage guiding surfaces and ring flanges
Contact between roller end faces and ring ribs

If bearing steel has poor wear resistance, excessive material loss will occur, resulting in reduced dimensional accuracy, increased vibration, and shortened bearing life. Therefore, excellent wear resistance is an essential property of rolling bearing steel.

3. High Elastic Limit

Rolling bearings operate with very small contact areas. Under load, especially heavy load conditions, contact stresses become extremely high.

To prevent plastic deformation and surface cracking under such conditions, bearing steel must exhibit a high elastic limit, ensuring that elastic deformation dominates and bearing geometry remains intact during operation.

4. Appropriate Hardness Level

Hardness has a direct and critical influence on contact fatigue life, wear resistance, and elastic limit. It is one of the most important quality indicators of rolling bearings.

However, hardness must be carefully optimized:

Higher hardness improves fatigue resistance and wear resistance
Excessively high hardness reduces toughness and increases the risk of brittle fracture
Lower hardness improves impact resistance but may reduce fatigue life

For bearings subjected to heavy impact loads—such as rolling mill bearings or certain automotive bearings—slightly reduced hardness is often necessary to improve toughness and operational safety.

5. Adequate Toughness

Many bearings experience impact loads during operation. Therefore, rolling bearing steel must maintain a suitable level of toughness to resist crack initiation and propagation.

Bearings used in severe impact conditions, such as railway bearings and rolling mill bearings, often require materials with enhanced impact toughness and fracture resistance. In such cases, bainitic heat treatment or carburized bearing steels are commonly used.

6. Dimensional Stability

Rolling bearings are precision mechanical components manufactured with micrometer-level accuracy. Any dimensional change caused by internal stress release or microstructural transformation during storage or service can lead to loss of precision.

Thus, bearing steel must exhibit excellent dimensional stability after heat treatment and during long-term operation.

7. Corrosion Resistance

Due to the long production cycle and multiple processing steps, bearing components may be stored as semi-finished or finished products for extended periods.

Bearing steel should provide basic corrosion resistance, particularly in humid environments, to prevent rust formation that could compromise surface quality and performance.

8. Good Processability

Bearing components undergo numerous cold and hot processing steps, including forging, machining, grinding, and heat treatment. Therefore, bearing steel must offer: