The quenching quality of bearing parts in heat treatment mainly depends on the quenching heating condition and cooling condition, and the cooling condition mainly depends on the selection of the corresponding quenching oil and cooling technology.

The bearing parts are mainly quenched by mineral oil.Mineral oils are composed of paraffins, bad alkanes, aromatic hydrocarbons and paraffin-aromatic series of hydrogen compounds and their derivatives.Because of the different composition and refining method, the special quenching oil with different characteristics and different USES is formed.According to the use requirements (including cooling speed, temperature, brightness, etc.) can be divided into common quenching oil, fast quenching oil, ultra-speed quenching oil, graded quenching oil, vacuum quenching oil, fast bright quenching oil and mechanical oil.

When selecting quenching oil, factors such as material, shape, size, depth of deformation quenching layer, technology, brightness and heat treatment equipment must be fully considered.The excellent quenching oil is made of refined base oil with high thermal stability (usually paraffin base) and various additives which can improve the service performance and service life.For rolling bearing parts in the quenching cooling process, the pearlite type should be prevented from changing, so as to avoid quenching opaque or local troostite, soft spots and other defects.Therefore, the cooling speed of quenching oil is higher than the critical cooling speed of bearing steel.However, the cooling speed should not be too large, so as not to cause greater internal stress, resulting in cracking and excessive quenching deformation.According to the C curve of GCr15 bearing steel austenite is the most easy to change the temperature about 650 ℃ and 450 ℃, the temperature must be fast before, and the temperature in the future, can slow cooling, especially at the beginning of the martensitic transformation point between Ms and Mf slow cooling can reduce the deformation and crack, but also cannot too slow, or austenitic retrogradation stability of retained austenite content easy cause increased.So you can choose at 650 ℃ and 450 ℃ cold cold speed is greater than the critical speed, and in the cold slow temperature after the oil quenching oil. In normal conditions, due to different site conditions and difficult to determine the critical cooling rate of the steel under different conditions. But in the scene can be judged according to the factors influencing the critical cooling rate of the critical cooling rate change trend, therefore to select the quenching oil. Such as high quenching temperature and holding time is long, the original organization, is the critical cooling rate will be smaller, this is the quenching oil can choose the cooling capacity is small.

For bearing rings with large wall thickness, if sufficient quenching layer is obtained, the quenching oil shall have a faster cooling rate.For thin-walled bearing rings, the quenching oil should have a slower cooling rate.For the parts with complex shape, the quenching oil with short film stage and fast cooling speed should be selected.

For the requirements of small deformation of the bearing ring, it is best to choose the graded quenching oil.When the temperature of bearing steel ring is classified above Ms point, the cooling speed reaches the critical cooling rate.