use of NSK Bearings
Matters needing attention during the use of NSK Bearings
2022-08-01
Fag bearing heat treatment
Fag bearing heat treatment classification and hardness testing method
2022-08-02

Factors affecting the service life of imported bearings and control methods

  1. The early failure forms of rolling bearings mainly include fracture, plastic deformation, wear, corrosion and fatigue. Under normal conditions, it is mainly contact fatigue. In addition to the service conditions, the failure life of imported bearing parts is mainly restricted by the hardness, strength, toughness, wear resistance, corrosion resistance and internal stress state of the steel.
life of imported bearings

Life of imported bearings of martensite in quenched steel

  1. When the original structure of high carbon chromium steel is granular pearlite, the carbon content of quenched martensite obviously affects the mechanical properties of the steel in the quenching and low temperature tempering state. The strength and toughness are about 0.5%, the contact fatigue life is about 0.55%,life of imported bearings and the compressive collapse capacity is about 0.42%. When the carbon content of quenched martensite of GCr15 steel is 0.5% – 0.56%, the comprehensive mechanical properties with strong failure resistance can be obtained.
life of imported bearings

Life of imported bearings of retained austenite in quenched steel

  1. High carbon chromium steel can contain 8% – 20% AR (residual austenite) after normal quenching. AR in imported bearing parts has both advantages and disadvantages. In order to promote advantages and eliminate disadvantages, life of imported bearings the content of AR should be appropriate. Because the amount of AR is mainly related to the austenitizing conditions of quenching heating, and its amount will affect the carbon content of quenched martensite and the amount of undissolved carbide, it is difficult to correctly reflect the impact of AR on mechanical properties.

  2. Therefore, the austenite heat stabilization treatment process was used to obtain different ar content under the fixed austenite condition. Here, the effect of AR content on the hardness and contact fatigue life of GCr15 steel after quenching and low temperature tempering was studied. With the increase of austenite content,life of imported bearings the hardness and contact fatigue life increase, and then decrease after reaching the peak value. However, the peak value of AR content is different. The peak value of hardness appears at about 17% AR, while the peak value of contact fatigue life appears at about 9%.

life of imported bearings

Life of imported bearings of undissolved carbides in quenched steel

  1. The quantity, morphology, size and distribution of undissolved carbides in quenched steel are affected not only by the chemical composition of the steel and the original structure before quenching, but also by the austenitizing conditions. There are few studies on the influence of undissolved carbides on the service life of imported bearings.

  2.  Carbide is a hard brittle phase. In addition to being beneficial to wear resistance, it will cause cracks due to stress concentration with the matrix (especially when the carbide is non spherical), which will reduce toughness and fatigue resistance. In addition to its own influence on the properties of steel, quenched undissolved carbides also affect the carbon content and AR content and distribution of quenched martensite, thus having an additional impact on the properties of steel.

  3. Therefore, too many quenched insoluble carbides are harmful to the comprehensive mechanical properties and failure resistance of steel. Properly reducing the carbon content of imported bearing steel is one of the ways to improve the service life of parts.

  4. In addition to the quantity of quenched undissolved carbides, the size, morphology and distribution also affect the material properties. In order to avoid the harm of undissolved carbides in imported bearing steel, it is required that undissolved carbides are small (small in quantity), small (small in size), uniform (the difference between sizes is very small, and the distribution is uniform), and round (each carbide is spherical). 

  5. It should be pointed out that it is necessary for imported bearing steel to have a small amount of undissolved carbide after quenching, which can not only maintain sufficient wear resistance, but also be a necessary condition for obtaining fine grain cryptocrystalline martensite.

Life of imported bearings of residual stress after quenching and tempering

  1. After quenching and low temperature tempering, the imported bearing parts still have large internal stress. The residual internal stress in the parts has advantages and disadvantages. After heat treatment life of imported bearings, the fatigue strength of steel increases with the increase of residual compressive stress on the surface.
  2.  On the contrary, when the residual internal stress on the surface is tensile stress, the fatigue strength of steel decreases. Therefore, it is also one of the measures to improve the service life to make the imported bearing parts have large residual compressive stress on the surface after quenching and tempering.
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