Basic performance requirements for steel for rolling bearing
In the actual use of rolling bearing parts, they often have to work at high speed and for a long time under complex stress states and high stress values such as tensile, compression, bending, shear, alternating and so on. The selection of the appropriate material for the manufacture of rolling bearings will have a great impact on their performance and life. The basic method of selecting materials is determined according to the form of failure (failure) of the bearing. In general, the main form of failure of rolling bearings is fatigue peeling under alternating stress, and the loss of bearing accuracy due to frictional wear, in addition, there are abnormal failure of bearings caused by cracks, pressure pits, rust and other reasons. Therefore, in general, rolling bearings should have high resistance to plastic deformation, less frictional wear, good rotational accuracy, high dimensional accuracy, good dimensional stability, and long contact fatigue life. And many of these properties are determined by a combination of materials and heat treatment processes. Therefore, the material for manufacturing rolling bearings is required to have the following properties after certain heat treatment in the post-process.
1. High contact fatigue performance
When the rolling bearing is running, when the rolling element rolls between the raceways of the inner and outer rings of the bearing, its contact part is subjected to periodic alternating loads, which are tens of thousands or hundreds of thousands of times per minute. Under the repeated action of periodic alternating stress, fatigue peeling of the contact surface appears. After peeling, the vibration and noise of the bearing increase, and the operating temperature continues to rise, resulting in the final fatigue failure of the bearing and can not be used. Contact fatigue failure is the main form of rolling bearing failure. Therefore, it is required that the steel used for rolling bearings should have high contact fatigue strength.
2. High wear resistance
When rolling bearings work normally, in addition to rolling friction, sliding friction is also accompanied. 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 hole, the contact surface of the cage and the ferrule guiding flange, the contact surface of the roller end face and the ferrule flange. The presence of sliding friction in rolling bearings inevitably causes wear on bearing parts. If the wear resistance of the bearing steel is poor, the rolling bearing will lose the bearing accuracy prematurely due to wear or the vibration of the bearing will increase due to the decrease in the rotational accuracy of the bearing, and the life will decrease. Therefore, bearing steels are required to have high wear resistance.
3. High elastic limit
When rolling bearings work, due to the small contact area between the rolling elements and the inner and outer rings, the contact stress of the contact surface is very large when the bearing is under load, especially when bearing a large load, in order to prevent plastic deformation under high contact stress, so as to destroy the accuracy of the bearing and produce surface cracks, so the bearing steel should have a high elastic limit.
4. Suitable hardness
Hardness has a very close relationship with contact fatigue life, wear resistance, elastic limit, so the hardness of rolling bearings also directly affects the life of rolling bearings, so hardness is one of the important indicators of rolling bearings. The hardness of rolling bearings is usually determined according to the way and size of the bearing load, bearing size and wall thickness, and too high or too low hardness will affect the life of the bearing. As we all know, the main failure form of rolling bearings is contact fatigue failure; Poor wear resistance or dimensional instability resulting in loss of bearing accuracy; Bearing parts lack certain toughness, and brittle fracture occurs under large impact load, resulting in bearing failure. It is necessary to determine the hardness of the bearing according to the specific situation of the bearing and the way of failure. For the loss of bearing accuracy due to fatigue peeling failure or poor wear resistance of bearing parts, higher hardness should be selected for bearing parts; For bearings subjected to large shock loads (such as rolling mill bearings, some automotive bearings, etc.), it is necessary to appropriately reduce the hardness to improve the toughness of the bearing.
5. A certain toughness
Many bearings are subjected to a certain impact load during use, so the bearing steel is required to have a certain toughness to ensure that the bearing is not damaged by the impact load. For bearings bearing large impact loads, such as rolling mill bearings, railway bearings, etc., materials are required to have relatively high impact toughness and fracture toughness, some of these bearings are quenched with bainite, and some are carburized steel, which is to ensure that these bearings have better impact resistance.
6. Good dimensional stability
Rolling bearings are precision mechanical parts whose accuracy is measured in microns. In the long-term storage and use of the bearing, the accuracy of the bearing cannot be lost due to the change of bearing size caused by the change of the internal structure or stress of the bearing parts. Therefore, the bearing steel is required to have good dimensional stability.
7. Certain anti-rust performance
Due to the many production processes of rolling bearings, the production cycle is long, and some semi-finished products or finished parts need to be stored for a long time before assembly, so bearing parts are prone to certain rust in the production process or in the preservation of finished products, especially in humid air. Therefore, steel for rolling bearings is required to have certain rust resistance.
8. Good process performance
In the production process of rolling bearings, the parts need to go through multiple cold and hot processing processes, which requires that the bearing steel should have good processing performance, such as cold and hot forming performance, cutting performance, grinding processing performance, heat treatment performance, etc., to meet the production needs of rolling rolling bearings in large quantities, high efficiency, low cost and high quality. In addition, in addition to the above basic requirements, the bearing steel used under special working conditions should also have corresponding special performance requirements, such as high temperature resistance, high speed performance, corrosion resistance and non-magnetic performance.
