Basic Performance Requirements For NTN Bearing Steel

Rolling bearing materials include rolling bearing parts materials and cages, rivets and other auxiliary materials. Rolling bearings and their parts are mostly made of steel, and the steel used for rolling bearings is usually high carbon chromium steel and carburized steel. With the development of modern science and technology and the increasing use of rolling NTN bearings, more and more high requirements for NTN bearings, 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 and other fields.

 The basic requirements for materials of rolling NTN bearings depend to a large extent on the working performance of NTN bearings. Whether the material selected for manufacturing rolling NTN bearings is suitable will have a great impact on its service performance and life. In general, the main failure form of rolling NTN bearings is fatigue spalling under alternating stress and loss of accuracy of NTN bearings due to friction and wear. In addition, there are cracks, indentation, rust and other reasons to cause 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 both the material and the heat treatment process. Since the basic requirements for materials of rolling NTN bearings are determined by the failure form of NTN bearings, the materials for manufacturing rolling NTN bearings are required to have the following properties after certain heat treatment in the post-process:

1. High contact fatigue strength

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

2. High wear resistance

  When rolling NTN bearings work normally, they are accompanied by sliding friction in addition to rolling 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 pocket hole, between the cage and the ring guide guard, and between the roller end face and the ring guide guard. The existence of sliding friction in rolling NTN bearings inevitably leads to wear of NTN bearing parts. If the wear resistance of the NTN bearing steel is poor, the rolling NTN bearing will lose accuracy prematurely due to wear or increase the vibration and reduce the life of the NTN bearing due to the decrease of rotation accuracy. Therefore, it is required that NTN bearing steel should have high wear resistance.

3. High elastic limit

  When rolling NTN bearing works, because the contact area between the rolling body and the raceway of the ring is very small, the contact pressure of the contact surface of the NTN bearing is very large when it is under load, especially when it is under large load. In order to prevent excessive plastic deformation under high contact stress, resulting in loss of precision or surface crack of NTN bearing, it is required that NTN bearing steel should have a high elastic limit.

4.Suitable hardness

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

  Many rolling NTN bearings will be affected in the process of use. The impact load is fixed, so the NTN bearing steel is required to have a certain toughness, in order to ensure that the NTN bearing is not destroyed by impact. For NTN bearings bearing larger impact loads, such as rolling mill NTN bearings, railway NTN bearings and other required materials have relatively high impact toughness and fracture toughness. Some of these NTN bearings use bainite quenching heat treatment process, and some use carburized steel materials, in order to ensure that these NTN bearings have better impact toughness.
6.Good dimensional stability

  Rolling NTN bearings are precise mechanical parts whose accuracy is calculated in microns. In the long-term storage and use process, changes in the internal structure or stress will cause changes in the size of NTN bearings, resulting in the loss of accuracy of NTN bearings. Therefore, in order to ensure the dimensional accuracy of NTN bearing, NTN bearing steel should have good dimensional stability.
7. Good rust resistance

  Rolling NTN bearing has many production processes and a long production cycle, and some semi-finished or finished parts need to be stored for a long time before assembly. Therefore, certain corrosion of NTN bearing parts is easy to occur in the production process or in the storage of finished products, especially in the humid air. Therefore, it is required that NTN bearing steel should have good rust prevention performance.

8 .Good technological performance

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

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