The basic material requirements of rolling bearings depend largely on the working performance of the bearings.Whether the material of rolling bearing is suitable or not will have a great influence on its performance and service life.In general, the main failure forms of rolling bearings are fatigue spalling under the action of alternating stress and loss of bearing precision due to friction and wear.In addition, there are cracks, indentation, corrosion and other reasons for the abnormal damage of the bearing.Therefore, rolling 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 the properties are determined by materials and heat treatment processes.Since the basic material requirements of rolling bearings are determined by the failure form of the bearings, it is required that the materials for manufacturing rolling bearings should have the following properties after certain heat treatment in the post-process:
High wear resistance
When the rolling bearing works normally, there is not only rolling friction, but also 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 pocket hole of the cage, the contact surface between the cage and the guide edge of the ring, and the guide edge between the end face of the roller and the guide edge of the ring, etc.The existence of sliding friction in rolling bearing inevitably causes the bearing parts to wear.If the bearing steel wear resistance is poor, the rolling bearing will lose the precision due to wear or the vibration will increase and the service life of the bearing will decrease due to the decrease of the rotating precision.Therefore, bearing steel is required to have high wear resistance.
High contact fatigue strength
Contact fatigue failure is the main form of bearing failure.During the operation of the rolling bearing, the rolling body rolls between the raceway of the inner and outer rings of the bearing. The contact part of the rolling body is subject to periodic alternating loads, which can reach hundreds of thousands of times per minute. Under the repeated action of periodic alternating stresses, fatigue spalling occurs on the contact surface.When the rolling bearing begins to peel off, it will cause the vibration and noise of the bearing to increase and the working temperature will rise sharply, resulting in the ultimate damage of the bearing. This damage form is called contact fatigue damage.Therefore, it is required that the steel used for rolling bearing should have high contact fatigue strength.
Three high elastic limits
When the rolling bearing works, because the contact area between the rolling body and the ring raceway is small, the contact pressure on the contact surface of the bearing is very large when it bears the load, especially when it bears a large load.In order to prevent excessive plastic deformation under high contact stress, which may result in loss of bearing precision or surface crack, the bearing steel is required to have a high elastic limit.
Hardness is one of the important indexes of rolling bearing.It is closely related to the contact fatigue strength, wear resistance and elastic limit of the material, which directly affects the life of the rolling bearing. The hardness of the bearing is usually determined by the way and size of the bearing bearing load, the bearing size and the overall condition of the wall thickness.The hardness of rolling bearing steel should be suitable, too large or too small will affect the service life of the bearing.As is known to all, the main failure forms of rolling bearings are contact fatigue failure and loss of bearing precision due to poor wear resistance or dimensional instability.If the bearing parts lack a certain toughness, the bearing will be damaged due to brittle fracture when it bears a large impact load.Therefore, it is necessary to determine the hardness of the bearing according to the specific conditions of the bearing and the way of damage.For the loss of bearing precision due to fatigue spalling or poor wear resistance, the bearing parts should choose a higher hardness;It is necessary to reduce the hardness of the bearing to improve the toughness of the bearing for bearing bearing heavy impact load (such as rolling mill bearing, railway bearing and some automobile bearing, etc.).
Certain impact toughness
Many rolling bearings will be subjected to a fixed impact load in the process of use, so the bearing steel is required to have a certain toughness, in order to ensure that the bearing will not be damaged by impact.For bearing bearing a large impact load, such as rolling mill bearings, railway bearings and other materials required to have relatively high impact toughness and fracture toughness, some of these bearings with bainite quenching heat treatment process, some with carburizing steel material, is to ensure that these bearings have a good impact toughness.
Good dimensional stability
Rolling bearing is a precise mechanical part, its precision is calculated in micron.In the long-term storage and use process, the bearing size will change due to the change of internal structure or stress, resulting in the loss of precision of the bearing.Therefore, in order to ensure the dimensional accuracy of the bearing, the bearing steel should have good dimensional stability.
Good rust resistance
The production process of rolling bearing is various and the production cycle is long. Some semi-finished or finished parts need to be stored for a long time before assembly. Therefore, certain corrosion of bearing parts is very easy to occur in the production process or in the storage of finished products, especially in humid air.Therefore, the bearing steel is required to have good rust resistance.
Good process performance
Rolling bearing in the production process, its parts to go through a number of cold, hot processing procedures.This requires that the bearing steel should have good technological performance, such as cold and hot forming performance, cutting, grinding performance and heat treatment performance, etc., in order to adapt to the rolling bearing mass, high efficiency, low cost and high quality production needs.
In addition, for the bearing used under special working conditions, in addition to the above basic requirements, the steel must also put forward the corresponding special performance requirements, such as high temperature performance, high speed performance, corrosion resistance and anti-magnetic properties.