A large number of application practice and life tests have shown that the bearing failure is mostly contact surface fatigue.GB/T24611-2020/1S015243:2017 will fatigue listed in the bearing six common failure modes of the first, was listed in the sixth place of fracture in the formation process is also due to fatigue reasons, known as fatigue fracture. Typical fatigue failure is divided into subsurface origin type and surface origin type.

First, sub-surface origin fatigue

Rolling contact large contact stress occurs at a certain depth under the surface of a certain place, in the repeated action of alternating stress, the formation of fatigue sources (microcracks) in the place. Crack source in the cyclic stress gradually to the surface expansion, the formation of open sheet cracks, and then be torn into flaky particles from the surface spalling, resulting in pockmarks, pits. If the bearing steel there is some kind of weak point, or defects (common such as non-metallic inclusions, air gaps, coarse carbide crystal interface), will accelerate the formation of fatigue sources and fatigue crack expansion, greatly reducing the fatigue life.

Third, fatigue fracture

The origin of fatigue fracture is too tight with the assembly stress and cyclic alternating stress formed by fatigue yield, assembly stress, alternating stress and yield limit of the balance between once lost, it will be along the collar axis direction of fracture, the formation of penetrating cracks.

In practice the normal use of the bearing failure, the damage is mostly as described above, that is, the contact surface fatigue, and the three types of fatigue failure and the sub-surface origin fatigue is common, AS0281 and IS0281/amd.2 recommended bearing life calculation method is based on the sub-surface origin fatigue as a basis for the derived.

Commonly used anti-fatigue methods are:

A, heat treatment technology

Heat treatment is commonly used to improve the mechanical properties of materials process methods, in order to adapt to the different material parts of different use requirements, the need to choose a different heat treatment process, pre-heat treatment organization, quenching heating temperature, heating rate, cooling mode (medium and speed), tempering temperature and time, etc. have a significant impact on the mechanical properties, to optimize the many heat treatment parameters, combinations, in order to adapt to the use of conditions To optimize and combine the many heat treatment parameters, in order to adapt to the conditions of use of good performance, thereby extending the fatigue life of the parts. Build heat treatment virtual production platform, promote heat treatment technology to high-tech knowledge-intensive transformation. Optimization of heat treatment process parameters and the development of digital heat treatment technology is an important prerequisite for the realization of anti-fatigue manufacturing.

B, surface chemical heat treatment

Surface chemical heat treatment of the modified role is mainly in the surface, according to different requirements, select the infiltration of chemical elements, such as carburizing and quenching and tempering to improve the surface hardness, but the distortion of the workpiece is not easy to control: nitriding after the formation of metal nitride to obtain higher surface hardness and abrasion, corrosion resistance and fatigue resistance, and the distortion of the workpiece is small, but the efficiency is not high; co-infiltration process to make the hardness, abrasion, corrosion, fatigue resistance Better performance, and less quenching distortion, but the hardening layer is thin, not suitable for heavy-duty workpiece. The direction of development of surface chemical heat treatment is to expand the application of low-temperature chemical treatment, improve the quality of the penetration layer, accelerate the process, the development of environmentally friendly technology, composite penetration process and analog digital processing technology.

c, the application of surface strengthening technology

Traditional surface strengthening technology originated from the principle of cold hardening, such as shot blasting, sand blasting, shot blasting, etc., the new surface strengthening technology such as laser surface hardening, laser shot blasting surface hardening, ultrasonic tumbling hardening, chemical methods of surface hardening, composite surface hardening of a variety of processes of the new technology has been successfully applied in many fields, such as laser a shot blasting process (laser impact treatment), the use of high-energy pulsed laser in the formation of the parts surface Shock wave, so that the surface material to produce compression and plastic deformation, the formation of residual compressive stress on the surface, thereby enhancing the fatigue resistance (such as stress crack resistance, corrosion fatigue, etc.).

D, surface modification technology

Commonly used surface modification techniques mainly include ion implantation and surface coating.

Ion injection is a non-high-temperature process, there is no metallurgy and equilibrium phase diagram limitations, according to the different needs of different injected elements and dosage in order to obtain the expected surface properties. For example, chromium ions are injected to enhance the corrosion and fatigue resistance of the substrate material; boron ions are injected to enhance the wear resistance of the substrate.

Surface coating technologies include physical vapor deposition (PVD), chemical vapor deposition (CVD) radio frequency sputtering (RF) ion spraying (PSC), chemical plating and so on.

In addition, the ion seepage process in a certain degree of vacuum using high-voltage direct current to be seeped elements in the ionic state, so that the resulting ionic current bombardment of the surface of the workpiece, the formation of compounds on the surface to achieve the purpose of reducing friction and improve wear resistance.

E, microfabrication and finishing technology

As an advanced manufacturing technology, high-precision microfabrication and blending, optical finishing technology, but also to improve the fatigue resistance of basic parts play an important role. Ultra-precision grinding, eddy current finishing process to reduce the surface roughness of the workpiece for the purpose of processing the surface physical and chemical properties, mechanical properties, the contour shape of the contact are beneficial changes can be corrected contact stress distribution, conducive to the formation of power lubricant film, improve fatigue life.