What are the methods of hardening bearings? How to prevent quenching deformation?

A, the purpose of bearing quenching treatment

　　The purpose of bearing quenching is to improve the hardness, strength, wear resistance and fatigue degree of the bearing, and to obtain high dimensional stability and comprehensive mechanical properties through tempering. After quenching, the microstructure consists of cryptocrystalline martensite and fine crystalline martensite, fine thermally uniform distribution of residual carbide and residual austenite. The relative amount and distribution of these organizations will determine the performance of bearing steel.

　　Second, the main several bearing quenching method

　　Quenching and hardening for the purpose of bearing quenching methods are various, in most cases can be broadly divided into overall quenching, carburizing quenching, high-frequency quenching, carbonitriding, etc..

　　1, the overall quenching: overall quenching is a common bearing heat treatment process, the majority of materials used in high-carbon chromium bearing steel (GCr15). In the heat treatment furnace heated to about 840 ℃, and make the carbide formed by spheroidal annealing in the matrix moderate, uniform solid solution, and then quenched and cooled, the implementation of low-temperature tempering. Through the insoluble carbide and tempering precipitation of carbide, to obtain a uniform precipitation organization, can be used for the requirements of wear-resistant bearings.

　　2, carburizing quenching: carburizing quenching is in the heat treatment furnace will be low carbon alloy steel at about 930 ℃ insulation, management of carburizing gas in the furnace, from the surface to the internal carbon penetration diffusion, quenching heat treatment, due to the gradient of carbon concentration, quenching surface hardening, because the internal hardness is lower than the surface, for the requirement of impact resistance bearings.

　　3, high-frequency quenching: high-frequency quenching is the use of induction heating heat treatment, mainly for medium carbon steel, applied to the shape of complex automotive wheels with bearings, etc., only harden the necessary parts.

　　4, carbonitriding: carbonitriding is the addition of about 5% of ammonia in the carburizing gas, precipitating nitride near the surface layer. Considering the difference in solubility of carbon and nitrogen in austenite, it is usually treated at 750~850℃ below the carburizing temperature, which is especially effective for the long life of bearings used in the environment where foreign materials are mixed.
Robot speed reducer bearings
　　Second, to reduce and prevent bearing quenching deformation methods

　　1、The cause of bearing quenching deformation

　　Bearing ring quenching caused by deformation and size expansion and contraction, are due to the combined effect of thermal stress and tissue stress. Influence the cause of ring expansion and contraction depends mainly on the content of the quenching organization of each phase components. The more residual austenite content, the less the number of martensite, the smaller the volume change. In addition, the collar wall thickness, quenching medium, cooling methods have an impact on the expansion and contraction of the collar.

　　Collar deformation mainly has a radial uneven deformation (roundness exceeds) and axial uneven deformation (flatness exceeds) two. The reason is the difference in time between the various parts of the ring to reach Ms point, causing the martensite transformation is not isochronous, resulting in inconsistent tissue stress. In addition, the furnace temperature is not uniform, improperly loaded furnace, inconsistent cooling rate, operation of mutual collision, will increase the deformation.

　　2, to reduce or prevent deformation methods

　　Quenching and heating using the secondary heating method, that is, the first 650 ~ 700 ℃ preheating, and then rise to the process temperature to ensure uniform heating, but also to eliminate the original stress before quenching; using hot oil (100 ~ 140 ℃) cooling or graded quenching, reduce the time difference between the parts to reach Ms point on the thin-walled deformable collar, try to use the forced to prevent deformation of the fixture (quenching press).