What Are The Basic Performance Requirements Of NTN Bearing Steel?

Rolling bearing materials include rolling bearing parts materials and cages, rivets and other auxiliary materials. The rolling bearing and its parts are mostly made of steel, and the rolling bearing steel is usually high carbon chromium steel and carburizing steel. With the development of modern science and technology and the increasing use of rolling NTN bearings, the requirements for NTN bearings are higher and higher, such as high precision, long life and high reliability. For some special purpose NTN bearings, NTN bearing materials are also required to have high temperature resistance, corrosion resistance, non-magnetic, ultra-low temperature, radiation resistance and other properties. In addition, NTN bearing materials also include alloy materials, non-ferrous metals and non-metallic materials. In addition, NTN bearings made of ceramic materials are now used in locomotive, automobile, subway, aviation, aerospace, chemical industry and other fields.

The basic requirements of rolling NTN bearings for materials largely depend on the working performance of NTN bearings. Whether the selection of materials for manufacturing rolling NTN bearings is appropriate will have a great impact on their service performance and life. In general, the main failure form of rolling NTN bearings is fatigue spalling under the action of alternating stress, and loss of accuracy of NTN bearings due to friction and wear. In addition, there are cracks, indentation, rust and other reasons that cause the abnormal damage of NTN bearings. Therefore, rolling NTN bearings should have high resistance to plastic deformation, less friction and wear, good rotation accuracy, good dimensional accuracy and stability, and long contact fatigue life. And many of these properties are determined by the material and heat treatment process. Because the basic material requirements of rolling NTN bearings are determined by the failure form of NTN bearings, it is required that the materials for manufacturing rolling NTN bearings should have the following properties after certain heat treatment in the post-process:

One high contact fatigue strength：

Contact fatigue failure is the main form of normal failure of NTN bearings. When the rolling NTN bearing is running, the rolling body rolls between the raceway of the inner and outer rings of the NTN bearing, and its contact part bears periodic alternating load, which can reach hundreds of thousands of times per minute. Under the repeated action of periodic alternating stress, fatigue peeling occurs on the contact surface. After the rolling NTN bearing starts to flake off, it will cause the vibration and noise of the NTN bearing to increase, and the working temperature will rise sharply, resulting in the final damage of the NTN bearing. This failure form is called contact fatigue failure. Therefore, it is required that the steel used for rolling NTN bearings should have high contact fatigue strength.

Two high wear resistance：
When rolling NTN bearing works normally, in addition to rolling friction, it is accompanied by sliding friction. The main parts of sliding friction are: the contact surface between the rolling body and the raceway, the contact surface between the rolling body and the cage hole, the cage and the ring guide edge and between the roller end face and the ring guide edge. The existence of sliding friction in rolling NTN bearing inevitably causes the NTN bearing parts to wear. If the wear resistance of the NTN bearing steel is poor, the rolling NTN bearing will prematurely lose its accuracy due to wear or decrease the rotation accuracy, which will increase the vibration and reduce the life of the NTN bearing. Therefore, it is required that NTN bearing steel should have high wear resistance.

Three high elastic limits：
  When the rolling NTN bearing is working, because the contact area between the rolling body and the raceway of the ring is very small, the contact pressure on the contact surface of the NTN bearing is very high when it is under load, especially under large load. In order to prevent excessive plastic deformation under high contact stress, so that the precision of NTN bearings is lost or surface cracks occur, therefore, it is required that NTN bearing steel should have a high elastic limit.

Four suitable hardness：

Hardness is one of the important indexes of rolling NTN bearings. It has a close relationship with the contact fatigue strength, wear resistance and elastic limit of materials, and directly affects the life of rolling NTN bearings. The hardness of NTN bearings is usually determined according to the way and size of NTN bearings bearing loads, the size of NTN bearings and the overall situation of wall thickness. The hardness of steel used for rolling NTN bearing should be appropriate. Too large or too small will affect the service life of NTN bearing. As we all know, the main failure form of rolling NTN bearings is contact fatigue failure, and the loss of accuracy of NTN bearings due to poor wear resistance or size instability; If NTN bearing parts lack a certain toughness, they will be damaged due to brittle fracture when they are subjected to large impact loads. Therefore, it is necessary to determine the hardness of NTN bearings according to the specific situation and failure mode of NTN bearings. For the loss of NTN bearing accuracy due to fatigue peeling or poor wear resistance, NTN bearing parts should be selected with higher hardness; For NTN bearings that bear large impact loads (such as rolling mill: NTN bearings, railway NTN bearings and some automobile NTN bearings, etc.), it is very necessary to reduce the hardness appropriately to improve the toughness of NTN bearings.

Five certain impact toughness：

Many rolling NTN bearings will be affected in the process of use. The fixed impact load, therefore requires the NTN bearing steel to have a certain toughness, to ensure that the NTN bearing is not destroyed by impact. For the NTN bearings that bear large impact load, such as rolling mill NTN bearings and railway NTN bearings, the materials are required to have relatively high impact toughness and fracture toughness. Some of these NTN bearings use bainite quenching heat treatment process, and some use carburizing materials, in order to ensure that these NTN bearings have better impact toughness.

Six High dimensional stability：

Rolling NTN bearing is a precise mechanical part, and its accuracy is calculated in micron. In the process of long-term storage and use, changes in the internal organization or stress will cause changes in the size of NTN bearings, leading to loss of accuracy of NTN bearings. Therefore, in order to ensure the dimensional accuracy of NTN bearings, NTN bearing steel should have good dimensional stability.

Seven good rust resistance：

The production process of rolling NTN bearings is various and the production cycle is long. Some semi-finished products or finished parts need to be stored for a long time before assembly. Therefore, NTN bearing parts are prone to certain rust in the production process or in the preservation of finished products, especially in humid air. Therefore, NTN bearing steel is required to have good antirust performance.

Eight Good process performance： 

In the production process of rolling NTN bearing, its parts should go through multiple cold and hot working procedures. This requires that NTN bearing steel should have good process properties, such as cold and hot forming properties, cutting, grinding processing properties and heat treatment properties, etc., in order to meet the needs of rolling NTN bearing mass, high efficiency, low cost and high quality production.

In addition, for the NTN bearing used under special working conditions, in addition to the above basic requirements, the corresponding special performance requirements for its steel must also be put forward, such as high temperature resistance, high speed performance, corrosion resistance and anti-magnetic property, etc.