What are the properties and requirements of bearing steel

The materials used for rolling bearings include rolling bearing parts, retaining frames, rivets, and other auxiliary materials. Rolling bearings and their components are mostly made of steel, and the steel used for rolling bearings is usually high carbon chromium steel and carburizing steel. With the development of modern science and technology and the increasing use of rolling bearings, the requirements for bearings are becoming higher and higher, such as high precision, long life, and high reliability. For some special purpose bearings, bearing materials are also required to have properties such as high temperature resistance, corrosion resistance, non-magnetic, ultra-low temperature, and radiation resistance. In addition, bearing materials also include alloy materials, non-ferrous metals, and non-metallic materials. In addition, bearings made of ceramic materials have been applied in fields such as locomotives, automobiles, subways, aviation, aerospace, and chemical engineering.

The basic material requirements for rolling bearings largely depend on the working performance of the bearings. The selection of materials for manufacturing rolling bearings will have a significant impact on their performance and lifespan. In general, the main forms of failure for rolling bearings are fatigue spalling under alternating stress and loss of bearing accuracy due to friction and wear. In addition, abnormal damage to bearings is caused by cracks, indentations, rust, and other factors. Therefore, rolling bearings should have high resistance to plastic deformation, minimal friction and wear, good rotational accuracy, good dimensional accuracy and stability, as well as long contact fatigue life. And many of these properties are jointly determined by materials and heat treatment processes. Due to the fact that the basic requirements for materials in rolling bearings are determined by the form of bearing failure, it is required that the materials used to manufacture rolling bearings should have the following properties after a certain heat treatment in the subsequent process:

High contact fatigue strength

Contact fatigue failure is the main form of normal bearing failure. When a rolling bearing is in operation, the rolling elements roll between the raceways of the inner and outer rings of the bearing, and their contact parts bear cyclic variable loads, some of which can reach hundreds of thousands of times per minute. Under the repeated action of cyclic variable stresses, fatigue peeling occurs on the contact surface. After the rolling bearing begins to peel off, it will cause the bearing to vibrate, increase noise, and the working temperature to rise sharply, resulting in the ultimate damage of the bearing. This form of damage is called contact fatigue failure. Therefore, it is required that the steel used for rolling bearings should have high contact fatigue strength.

High wear resistance

When rolling bearings work normally, in addition to rolling friction, there is also sliding friction. The main parts where sliding friction occurs are: the contact surface between the rolling element and the raceway, the contact surface between the rolling element and the cage pocket, the contact surface between the cage and the sleeve guide edge, and the contact surface between the roller end face and the sleeve guide edge. The existence of sliding friction in rolling bearings inevitably leads to wear of bearing components. If the wear resistance of bearing steel is poor, rolling bearings will lose accuracy prematurely due to wear or experience increased vibration and reduced lifespan due to decreased rotational accuracy. Therefore, it is required that the bearing steel should have high wear resistance.

High elastic limit

When rolling bearings are in operation, due to the small contact area between the rolling elements and the raceway of the ring, the contact pressure on the contact surface of the bearing is high when subjected to loads, especially when subjected to large loads. In order to prevent excessive plastic deformation under high contact stress, which may cause loss of bearing accuracy or surface cracks, it is required that bearing steel should have a high elastic limit.

Appropriate hardness

Hardness is one of the important indicators of rolling bearings. It is closely related to the material contact fatigue strength, wear resistance, and elastic limit, directly affecting the life of rolling bearings. The hardness of bearings is usually determined based on the way and size of the load they bear, the overall size and wall thickness of the bearings. The hardness of steel used for rolling bearings should be appropriate, as being too high or too low will affect the service life of the bearings. As is well known, the main failure modes of rolling bearings are contact fatigue damage and loss of bearing accuracy due to poor wear resistance or unstable dimensions; If the bearing parts lack a certain degree of toughness, they may suffer from brittle fracture when subjected to large impact loads, leading to bearing damage. So, the hardness of the bearing must be determined based on its specific condition and mode of damage. For situations where bearing accuracy is lost due to fatigue peeling or poor wear resistance, bearing parts should be selected with higher hardness; It is necessary to reduce the hardness appropriately to improve the toughness of bearings that bear large impact loads, such as rolling mill bearings, railway bearings, and some automotive bearings.

A certain level of impact toughness

Many rolling bearings are subjected to certain impact loads during use, so bearing steel is required to have a certain degree of toughness to ensure that the bearings are not damaged by impact. For bearings that bear large impact loads, such as rolling mill bearings and railway bearings, materials are required to have relatively high impact toughness and fracture toughness. Some of these bearings use bainitic quenching heat treatment technology, while others use carburizing steel materials to ensure that these bearings have good impact toughness.

Good dimensional stability

Rolling bearings are precision mechanical components, with precision measured in micrometers. During long-term storage and use, changes in internal organization or stress can cause changes in bearing size, resulting in loss of bearing accuracy. Therefore, to ensure the dimensional accuracy of bearings, bearing steel should have good dimensional stability.

Good rust prevention performance

The production process of rolling bearings is complex and the production cycle is long. Some semi-finished or finished parts need to be stored for a long time before assembly. Therefore, bearing parts are prone to certain rusting during the production process or storage of finished products, especially in humid air. So, it is required that the bearing steel has good anti rust performance.

Good process performance

During the production process of rolling bearings, their parts undergo multiple cold and hot processing steps. This requires bearing steel to have good processability, such as cold and hot forming performance, cutting and grinding performance, and heat treatment performance, etc., to meet the needs of large-scale, high-efficiency, low-cost, and high-quality production of rolling bearings.

In addition, for bearings used under special working conditions, in addition to the basic requirements mentioned above, corresponding special performance requirements must also be proposed for the steel used, such as high temperature resistance, high speed performance, corrosion resistance, and anti magnetic performance.